Grainger & Allison's Diagnostic Radiology, 5th Edition

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Grainger & Allison's Diagnostic Radiology, 5th Edition

Contributors † : deceased Andy Adam MBBS (Hons), FRCP, FRCS, FRCR, FFRRCSI (Hon) Professor of Interventional Radiolo

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Contributors



: deceased

Andy Adam MBBS (Hons), FRCP, FRCS, FRCR, FFRRCSI (Hon)

Professor of Interventional Radiology Department of Radiology St Thomas’ Hospital King’s College London London, UK E. Jane Adam MBBS, MRCP, FRCR Consultant Radiologist Department of Radiology St George’s Hospital London, UK Judith E. Adams MBBS, FRCR, FRCP Chair, Diagnostic Radiology Imaging Science and Biomedical Engineering University of Manchester Honorary Consultant Radiologist Royal Infirmary Manchester, UK David J. Allison BSc, MD, MRCS, LRCP, MBBS, DMRD, FRCR, FRCP

Emeritus Professor of Imaging Imperial College London, UK Sandra Allison MD Assistant Professor of Radiology Director, Radiology Residency Program Director, Ultrasound Georgetown University Hospital Washington DC, USA Philip Anslow FRCR Consultant Neuroradiologist Department of Radiology Radcliffe Infirmary Oxford, UK Susan M. Ascher MD Georgetown University Medical Center Washington DC, USA Zelena A. Aziz MD, MRCP, FRCR Consultant Radiologist Department of Radiology London Chest Hospital London, UK

Clive I. Bartram FRCS, FRCP, FRCR Emeritus Consultant, St Mark’s Hospital and Honorary Professor of Gastrointestinal Radiology Faculty of Medicine Imperial College London, UK Philip P. W. Bearcroft FRCP, FRCR Consultant Radiologist Department of Radiology Cambridge University Hospitals NHS Foundation Trust Addenbrooke’s Hospital Cambridge, UK Anna-Maria Belli DMRD, FRCR Consultant Vascular Radiologist and Reader in Radiology Department of Radiology St George’s Hospital London, UK Anthony R. Berendt BM, BCh, FRCP Consultant Physician-in-Charge Bone Infection Unit Nuffield Orthopaedic Centre Oxford, UK Lol Berman FRCP, FRCR University Department of Radiology Addenbrooke’s Hospital Cambridge, UK Martin J. K. Blomley†

Gisele Brasil Caseiras PhD Research Fellow Insitute of Neurology University College London London, UK Jackie E. Brown BDS, MSc, FDSRCP, DDRRCR Consultant Oral and Maxillofacial Radiologist Kings College London Dental Institute Guy’s Dental Hospital London, UK Dina F. Caroline MD, PhD Professor Emerita Department of Radiology Temple University Hospital Philadelphia Pennsylvania, USA Silvia D. Chang MD, FRCP(C) Assistant Professor University of British Columbia Department of Radiology Vancouver General Hospital Vancouver, Canada W. K. ‘Kling’ Chong BMedSci, MD, MRCP, FRCR Consultant Neuroradiologist Department of Radiology Great Ormond Street Hospital for Children NHS Trust London, UK Bairbre Connolly MBBCh, BAO, FRCSI, MCH, FFRRCSI, FRCP(C)

Carol A. Boles MD Associate Professor of Radiology Associate, Surgical Sciences Orthopedic Surgery Wake Forest University North Carolina, USA Jamshed B. Bomanji MBBS, MSc, PhD Consultant in Nuclear Medicine UCLH Trust Middlesex Hospital London, UK

Medical Director and Division Head of Image Guided Therapy Pediatric Interventional Radiologist Assistant Professor, University of Toronto Department of Diagnostic Imaging The Hospital for Sick Children Toronto, Canada Susan J. Copley MBBS, MD, MRCP, FRCR Consultant Radiologist and Honorary Senior Lecturer Radiology Department Hammersmith Hospital London, UK

x

CONTRIBUTORS

David O. Cosgrove MA, MSc, FRCP, FRCR Emeritus Professor Imaging Sciences Department Faculty of Medicine Imperial College Hammersmith Hospital London, UK

Robert J. Eckersley PhD Research Associate Imaging Sciences Department Faculty of Medicine Imperial College Hammersmith Hospital London, UK

Philip C. Goodman MD Professor of Radiology Chief, Thoracic Imaging Division Department of Radiology Duke University Medical Center Durham North Carolina, USA

Nigel Cowan PGDipLATHE, FRCP Oxford, UK

Andrew J. Evans MRCP, FRCR Consultant Radiologist Nottingham Breast Institute Nottingham City Hospital Nottingham, UK

Isky Gordon FRCR, FRCP Professor of Paediatric Imaging Institute of Child Health London, UK

Justin J. Cross MRCP, FRCR Consultant Neuroradiologist Department of Radiology Addenbrooke’s Hospital Cambridge, UK Paras Dalal BSc, MRCP, FRCR Research Fellow in Thoracic Imaging Department of Radiology Royal Brompton Hospital London, UK Maria Daskalogiannaki MD Registrar in Radiology Department of Radiology University Hospital of Heraklion Crete, Greece A. Mark Davies FRCR Consultant Radiologist Royal Orthopaedic Hospital Birmingham, UK Adrian K. Dixon MD, FRCR, FRCP, FRCS, FMedSci, FFRRCSI (Hon), FRANZCR (Hon)

Professor of Radiology Department of Radiology Addenbrooke’s Hospital University of Cambridge Cambridge, UK Rose de Bruyn DMRD, FRCR Consultant Radiologist Department of Radiology Great Ormond Street Hospital for Sick Children NHS Trust London, UK Claudio Defilippi MD Consultant Radiologist Department of Radiology OIRM - S. Anna Hospital Turin, Italy Sujal R. Desai MD, MRCP, FRCR Consultant Radiologist Department of Radiology King’s College Hospital London, UK

Jane Evanson BSc, MBBS, MRCP, FRCR Consultant Neuroradiologist, Barts & The London Hospital NHS Trust The Royal London Hospital London, UK Laura Fender BMedSci, BMBS, MRCP, FRCR Consultant Radiologist Nottingham University Hospital Nottingham, UK Alan H. Freeman MBBS, FRCR Consultant Radiologist Department of Radiology Addenbrooke’s Hospital Cambridge, UK Julia Gates MD Assistant Professor of Radiology Department of Radiology Tufts University School of Medicine Springfield Massachusetts, USA Robert N. Gibson MBBS, MD, FRANZCR, DDU Professor of Radiology Department of Radiology University of Melbourne Royal Melbourne Hospital Victoria, Australia Raymond J. Godwin MA, MB, Bchir, FRCP, FRCR Consultant Radiologist Department of Radiology West Suffolk Hospital Suffolk, UK Karen Goldstone BSc, MSc, Csci, FIPEM Radiation Protection Advisor Acting Head of Department of Medical Physics and Clinical Engineering East Anglian Regional Radiation Protection Service (EARRPS) Addenbrooke’s Hospital Cambridge, UK

Nicholas Gourtsoyiannis FRCR (Hon) Professor of Radiology University of Crete Faculty of Medicine Heraklion, Crete Greece Andrew J. Grainger BM, BS, MRCP, FRCR Consultant Radiologist Chapel Allerton Orthopaedic Centre Leeds Teaching Hospitals Leeds, UK Ronald G. Grainger MB ChB(Hons), MD, FRCP, DMRD, FRCR, FACR(Hon), FRACR(Hon)

Professor of Diagnostic Radiology (Emeritus) University of Sheffield Honorary Consultant Radiologist Royal Hallamshire Hospital and Northern General Hospital Sheffield, UK Philippe Grenier FRCR (Hon) Professor of Radiology Service de Radiologie Polyvalente Diagnostique et Interventionnelle Hôpital Pitié-Salpêtrière Paris, France Roxana S. Gunny BS, BSc, MRCP, FRCR Consulant Neuroradiologist Department of Radiology Great Ormond Street Hospital for Children NHS Trust London, UK Christine M. Hall MBBS, DMRD, FRCR MD Professor of Paediatric Radiology Great Ormond Street Hospital for Children NHS Trust London, UK David M. Hansell MD, FRCP, FRCR, LRSM Professor of Thoracic Imaging Department of Radiology Royal Brompton Hospital London, UK

CONTRIBUTORS

George G. Hartnell FRCR, FRCP Director of Cardiovascular and Interventional Radiology Department of Radiology Baystate Medical Center Springfield Professor of Radiology Tufts University Medical School Boston Massachusetts, USA Hedvig Hricak MD, Dr. Med, SC, Dr. h.c, FRCR (Hon) Chairman, Department of Radiology Carroll and Milton Petrie Chair Professor of Radiology, Weill Medical College of Cornell University Memorial Sloan-Kettering Cancer Center New York, USA James E. Jackson MRCP, FRCR Consultant Radiologist Department of Imaging Hammersmith Hospital London, UK H. Rolf Jäger FRCR, MD Reader in Neuroradiology Institute of Neurology University College London Honorary Consultant Neuroradiologist The National Hospital for Neurology and Neurosurgery and University College Hospital London, UK Jonathan J. James BMBS, FRCR Consultant Radiologist Nottingham Breast Institute Nottingham City Hospital Nottingham, UK Renee M. Kendzierski DO Assistant Professor of Radiology Department of Radiology Temple University Hospital Philadelphia Pennsylvania, USA Dow-Mu Koh MRCP, FRCP Senior Lecturer and Honorary Consultant Department of Radiology Royal Marsden Hospital Sutton, UK Isla Lang MBChB, MRCP, FRCR Consultant Paediatric Radiologist Sheffield Children’s Hospital Sheffield, UK

Adrian K. P. Lim MD, FRCR Consultant Radiologist and Senior Lecturer Imaging Sciences Department Faculty of Medicine Imperial College Hammersmith Hospital London, UK

Stuart E. Mirvis MD, FACR Professor of Radiology Department of Radiology University of Maryland School of Medicine Baltimore Maryland, USA

David J. Lomas MA, MB, BChir, FRCR, FRCP Professor of Clinical Magnetic Resonance Imaging Department of Radiology Addenbrooke’s Hospital Cambridge, UK

Sameh K. Morcos FRCS, FFRRCSI, FRCR Professor of Diagnostic Imaging University of Sheffield Consultant Radiologist Department of Diagnostic Imaging Northern General Hospital Sheffield, UK

Sharyn L. S. MacDonald MBChB, FRANZCR Consultant Radiologist Department of Radiology Christchurch Hospital Christchurch, New Zealand David MacVicar MA, MRCP, FRCP, FRCR Consultant Radiologist Department of Diagnostic Radiology Royal Marsden Hospital Sutton, UK Adrian Manhire BSc, MBBS, FRCP, FRCR Consultant Radiologist Nottingham City Hospital Nottingham, UK Tarik F. Massoud MA, MD, PhD, FRCR University Lecturer and Honorary Consultant in Neuroradiology University Department of Radiology University of Cambridge School of Clinical Medicine Addenbrooke’s Hospital Cambridge, UK Kieran McHugh FRCPI, DCH, FRCR Department of Radiology Great Ormond Street Hospital for Sick Children NHS Trust London, UK James Meaney FRCR, FFRRCSI Director of MRI St James’s Hospital Dublin, Ireland Hylton B. Meire FRCR, DRCOG, DMRD Consultant Radiologist (Retired) King’s College Hospital London, UK Kenneth A. Miles MD, FRCR, MSc, FRCP Clinical Imaging Sciences Centre Brighton and Sussex Medical School University of Sussex Falmar, Brighton, UK

Robert A. Morgan MBChB, MRCP, FRCR Consultant Radiologist Department of Radiology St George’s Hospital London, UK Iain Morrison MBBS, MRCP, FRCR Consultant Radiologist Radiology Department Kent and Canterbury Hospital Canterbury, UK Nestor L. Müller MD, PhD, FRCPC Professor and Chairman Department of Radiology University of British Columbia Head and Medical Director Department of Radiology Vancouver General Hospital Vancouver, Canada Graham Munneke MRCP, FRCR Consultant in Interventional Radiology Department of Radiology St. George’s Hospital London, UK Alison D. Murray MB ChB (Hons), FRCR, FRCP Senior Lecturer in Radiology Department of Radiology University of Aberdeen Aberdeen, UK Richard A. Nakielny FRCR Honorary Clinical Lecturer Directorate of Medical Imaging & Medical Physics Royal Hallamshire Hospital Sheffield, UK Hrudaya Nath MD Professor of Radiology Department of Radiology University of Alabama Hospitals Birmingham Alabama, USA

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xii

CONTRIBUTORS

Tony Nicholson MSc, FRCR Consultant Vascular Radiologist Department of Clinical Radiology Leeds Teaching Hospitals Leeds, UK Amaka C. Offiah BSc, MBBS, MRCP, FRCR, PhD Consultant Radiologist (Academic) Great Ormond Street Hospital for Children NHS Trust London, UK Simon Padley BSc, MBBS, FRCP, FRCR Consultant Radiologist Department of Radiology Chelsea and Westminster Hospital London, UK Martyn N. J. Paley PhD, FInstP Professor of MR Physics Academic Radiology University of Sheffield Sheffield, UK Nickolas Papanikolaou PhD Biomedical Engineer Department of Radiology University Hospital of Heraklion Crete, Greece Jai Patel MBChB, MRCP, FRCR Consultant Vascular Radiologist Department of Clinical Radiology St James’s University Hospital Leeds, UK Anne Paterson MBBS, MRCP, FRCR, FFR RCSI Consultant Paediatric Radiologist Radiology Department Royal Belfast Hospital for Sick Children Belfast, UK Praveen Peddu MRCS, FRCR Specialist Registrar in Radiology Department of Radiology King’s College Hospital London, UK A. Michael Peters BSc, MD, MSc, MRCP, MRCPath, FRCR

Professor of Nuclear Medicine Brighton and Sussex Medical School University of Sussex Brighton, UK William H. Ramsden BM, FRCR Consultant Paediatric Radiologist Department of Clinical Radiology St James’s University Hospital Leeds, UK

Sheila Rankin FRCR Consultant Radiologist Department of Radiology Guy’s and St. Thomas’ Foundation Trust London, UK

John Rout BDS, FDSRCS, MDentSc, DDRRCR, FRCR Consultant Oral and Maxillofacial Radiologist Birmingham Dental Hospital Birmingham, UK

Padma Rao MBBS, BSc, MRCP, FRCR,

Michael B. Rubens MB, DMRD, FRCR Consultant Radiologist Department of Radiology Royal Brompton Hospital London, UK

FRANZCR

Consultant Paediatric Radiologist Royal Children’s Hospital Parkville Melbourne Victoria, Australia Christine Reek BSc, FRCR Consultant Radiologist Department of Radiology Greenfield Hospital Leicester, UK John H. Reynolds DMRD, FRCR, MMedSci Consultant Radiologist Birmingham Heartlands Hospital Birmingham, UK Rodney H. Reznek FRANZCR (Hon), FRCP, FRCR Professor of Diagnostic Imaging The Centre for Cancer Imaging St Bartholomew’s Hospital and The London Queen Mary’s School of Medicine and Dentistry London, UK Philip M. Rich BSc, FRCS, FRCR Consultant Neuroradiologist Department of Neuroradiology Atkinson Morley Wing St George’s Hospital London, UK Andrea Rockall MD, BS, BSc, MRCP, FRCP Department of Radiology St Bartholomew’s Hospital London, UK Giles Roditi FRCP, FRCR Consultant Radiologist Department of Radiology Glasgow Royal Infirmary Glasgow, UK

Asif Saifuddin BSc (Hons), MBChB, MRCP, FRCR Consultant Radiologist Department of Radiology Royal National Orthopaedic Hospital NHS Trust Stanmore, UK Evis Sala MD, PhD, FRCR University Lecturer in Oncology Imaging University Department of Radiology Addenbrooke’s Hospital Cambridge, UK Caron Sandhu FRCR Consultant Radiologist Department of Radiology Guy’s and St. Thomas’ Hospital London, UK Dawn Saunders MD, MRCP, FRCR Consultant Neuroradiologist Department of Radiology Great Ormond Street Hospital for Children NHS Trust London, UK Daniel J. Scoffings MRCP, FRCR Specialist Registrar in Neuroradiology Addenbrooke’s Hospital Cambridge, UK Djilda Segerman MA, MSc, MIPEM Head of Nuclear Medicine Physics Department of Medical Physics Brighton and Sussex University Hospitals NHS Trust Brighton, UK

Lee F. Rogers MD Clinical Professor of Radiology Department of Radiology University of Arizona Health Services Tucson Arizona, USA

Kathirkama Shanmuganathan MD Associate Professor of Radiology Department of Radiology University of Maryland School of Medicine Baltimore Maryland, USA

Giles Rottenberg FRCR Consultant Radiologist Department of Radiology Guy’s and St. Thomas’ Foundation Trust London, UK

Ashley S. Shaw MRCP, FRCR Consultant Radiologist Department of Radiology Addenbrooke’s Hospital Cambridge, UK

CONTRIBUTORS

Mihra S. Taljanovic MD, MA Associate Professor of Clinical Radiology and Clinical Orthopedic Surgery Head - Musculoskeletal Imaging Section Department of Radiology Tucson Arizona, USA

Satinder P. Singh MD, FCCP Associate Professor of Radiology Director Cardiac CT Director, Combined Cardiopulmonary and Abdominal Fellowship Chief of Cardiopulmonary Radiology Department of Radiology University of Alabama Hospitals Birmingham Alabama, USA

FRCR

S. Aslam A. Sohaib MRCP, FRCR Radiology Department Royal Marsden Hospital London, UK

Consultant Radiologist Department of Clinical Radiology Great Ormond Street Hospital for Children NHS Trust London, UK

Alan Sprigg MBChB, DCH, DRCOG, DMRD, FRCR, FRCPCH

Consultant Paediatric Radiologist Sheffield Children’s Hospital Sheffield, UK John M. Stevens MBBS, DRACR, FRCR Lyshom Department of Neuroradiology Radiology Department The National Hospital for Neurology and Neurosurgery London, UK Dennis J. Stoker MB, FRCP, FRCS, FRCR Emeritus Consultant Radiologist Henley-on-Thames, UK Nicola H. Strickland BM BCh, MA (Hons),

Andrew M. Taylor BA (Hons), BM BCh, MRCP

Stuart Taylor BSc, MD, MRCP, FRCR Consultant Radiologist Department of Intestinal Imaging St Marks Hospital Northwick Park Harrow, UK Henrik S. Thomsen MD Professor and Chairman Department of Diagnostic Radiology Copenhagen University Hospital Herlev, Denmark Paolo Toma MD Radiologist-in-Chief Radiology Department G. Gaslini Institute Genoa, Italy

(Oxon), FRCP, FRCR

Consultant Radiologist Imaging Department Hammersmith Hospitals NHS Trust Honorary Senior Lecturer Imperial College London, UK Louise E. Sweeney MBBCH, BAO, DCH, DMRD, FRCR, FFR, RCSI

Consultant Paediatric Radiologist Radiology Department Royal Belfast Hospital for Sick Children Belfast, UK

Peter Twining FRCR, BSc, BS MB Consultant Radiologist Nottingham University Hospital Nottingham, UK John A. Verschakelen MD, PhD Professor of Chest Radiology Department of Radiology University Hospitals Gasthuisberg Leuven, Belgium

Sarah J. Vinnicombe BSc, MRCP, FRCR Consultant Radiologist Department of Radiology St Bartholomew’s Hospital London, UK Gustav K. von Schulthess MD, PhD Professor and Director Department of Radiology University Hospital Zurich, Switzerland Iain D. Wilkinson BSc, MSc, PhD, CSci, ARCP, FIPEM

Reader in Magnetic Resonance & Consultant Clinical Scientist Academic Radiology University of Sheffield and Sheffield Teaching Hospitals NHS Foundation Trust Sheffield, UK A. Robin M. Wilson FRCR, FRCP(E) Consultant Radiologist King’s College Hospital and Guy’s and St Thomas’ Foundation Trusts London, UK David J. Wilson MBBS, BSc, FRCP, FRCR Consultant Musculoskeletal Radiologist Nuffield Orthopaedic Centre and University of Oxford Oxford, UK Stuart J. Yates MSci, MSc, CSci, MIPEM Principal Physicist Department of Medical Physics & Clinical Engineering Cambridge University Hospitals NHS Foundation Trust Cambridge, UK

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Preface

We hope that this 5th edition of Diagnostic Radiology will continue to build on the original vision of Professors Grainger and Allison who, back in the early 1980s, saw the need for a ‘bible’ for doctors studying for postgraduate examinations in radiology, and to provide a bench book for reporting and reference. The success of the first four editions, which were extremely well received by an increasingly international readership, speaks for the realisation of their dream. Few could have predicted at that stage the extraordinary growth of radiology, or its increasing importance within all aspects of modern medicine. The unprecedented expansion in the imaging repertoire, together with the trend for increasing subspecialisation, have led to changes in training and in the methods used for teaching and learning. This book has had to evolve to reflect these changes, adapting to the perceived needs of those facing postgraduate examinations and also to all radiologists who wish to have an up-to-date basic general textbook for ready reference and illustration. An attempt to cover every subject in detail would have resulted in a huge book that would have been very difficult to use.We have chosen to concentrate on those subjects that most radiologists need to know well, and to pay special attention to the needs of trainee radiologists preparing for examinations. Because training throughout Europe is moving towards a three

year basic course followed by two years of training in selected subspecialties, the factual examination in the UK has moved to an earlier stage in training with less emphasis on some of the diagnostic rarities so beloved by examiners of old. The curriculum is now somewhat less comprehensive and the reduction in size of this 5th Edition reflects that – down from three volumes to two. In this electronic age there are many databases of images available on the internet, with accompanying text. Nevertheless, we believe that well structured textbooks remain an essential part of medical education and practice as they present information in a format that facilitates learning, guiding the reader through an unfamiliar field. We are convinced that Diagnostic Radiology will remain a valuable resource for many years to come. We are again extremely grateful to the distinguished international cast of authors who have all worked hard to deliver fresh and up-to-date material. We are also most grateful to Michael Houston, Gavin Smith and Nora Naughton for their professional skills and publishing expertise and to Jeremy Rabouhans for invaluable help with proof reading. We could never have done it without them! Andy Adam Adrian Dixon

Acknowledgements

This edition could not have occured without the large amount of work done by all the contributing authors and their colleagues. However, the vision and overall planning of Michael Houston at Elsevier have been fundamental in bringing the book to fruition. So, too, has the meticulous gathering and editing of material by Gavin Smith. Finally, the skilful copyediting, and other tasks provided by Nora Naughton, and her remarkable team, must not be forgotten; without them the Editors simply could not have managed. All of these col-

leagues remained remarkably cheerful throughout and kept strong heads even when chapters were late, images missing, and all the other hiccups that can hinder progress in a project of this kind. At a local level, all the Editors would like to thank their various secretaries, technicians and colleagues who have helped proofread, collect material and made various other invaluable contributions. The Editors

CHAPTER

Picture Archiving and Communication Systems (PACS) and Digital Radiology

1

Nicola H. Strickland

The role of PACS Advantages and disadvantages of PACS • Advantages of PACS • Disadvantages of PACS Planning for PACS • The PACS project team • Tendering for a PACS • The PACS contract • Economic considerations • Purchasing versus leasing a PACS • PRE-PACS workflow and preparation • Acronyms: DICOM, HL7 and IHE PACS project implementation • Implementation of digital image acquisition prior to PACS • Integration of PACS ‘Value-added’ PACS Modern PACS architecture • PACS networks • Storage requirements and solutions for PACS PACS workstations • Monitor quality on PACS workstations Conference room design Graphic user interface • Soft-copy tools Software concepts • Prefetching

Compression • Lossless • Lossy • Need for compression Digitization policy Teleradiology • Review of images from home • Teleradiology linkage between two or more hospitals for joint MDTMs • Outsourcing of imaging examinations for reporting • Tele-education Security • User-specific log-in and password • Monitor screen savers • Workstation time-outs • Encryption • Audit trails • Firewalls • Teleradiology security PACS training Quality assurance • Plain radiography • PACS workstations PACS housekeeping • Storage commitment • Modality performed procedure step Current and future directions of PACS

THE ROLE OF PACS A picture archiving and communication system (PACS) aims to replace conventional analogue film and paper clinical request forms and reports with a completely computerized electronic network whereby digital images are viewed on monitors in

conjunction with the clinical details of the patient and the associated radiological report displayed in electronic format. Clearly PACS must replace the functions of traditional X-ray film; i.e. image acquisition, storage, transportation and display.

4

SECTION 1

• IMAGING TECHNIQUES AND GENERAL ISSUES

Were these the only roles of a PACS, it would be an extremely complex and expensive means of replacing traditional film. A PACS must improve upon a film-based system, preferably in a cost-neutral manner. The major added value of a PACS is efficiency of data management. True efficiency benefits can only be realized once a PACS is at least hospital-wide, since any more limited installation means running two systems in parallel, i.e. it entails continuing to produce conventional film and moving it around the hospital, as well as the cost of installing and maintaining a PACS. Thus, even if funds are limited initially, it is advisable at least to aim and plan for growing the PACS installation into a hospital-wide system ultimately. This means decid-

ing upon a potential time scale in which the hospital-wide PACS is to be achieved, and deciding upon a scaleable PACS architecture. Ideally the whole hospital infrastructure should be adapted at the outset so that a hospital-wide PACS can be accommodated at a later stage. This includes providing an uninterruptable power supply (UPS), allowing sufficient cabling space in floors and ceilings, and adapting the air conditioning system for PACS. The hospital information technology (IT) network is likely to need upgrading to enable large amounts of image data to be transported, and it is advisable to install multiple PACS ‘drops’ (workstation outlets) so that more PACS workstations can easily be added at a later date.

ADVANTAGES AND DISADVANTAGES OF PACS Although the concept of PACS has now been in existence for over 20 years, advances in computer hardware technology only enabled it to become a realistic clinical entity in the 1990s. PACS installations are now rising exponentially worldwide, and although most institutions with PACS have achieved a completely filmless working environment, few function in a paperless mode. PACS has proved itself over the last 10 years in the clinical environment, however, and it would now be unthinkable not to implement PACS when installing a new imaging department, or a new hospital.

ADVANTAGES OF PACS There are a number of powerful advantages accruing from a hospital-wide PACS: • Once correctly acquired onto the PACS, no image can ever be lost or misfiled and is always available when needed.This is a major benefit considering that in many hospitals up to 20 per cent of conventional films are missing at the time they are clinically required. In addition to the convenience of always having the appropriate image available when it is wanted for viewing, no patient is re-irradiated simply because a previous key study has been lost. • PACS facilitates the easy comparison of a patient’s current and historical examinations, and of examinations performed on the same body part using different imaging techniques, which is desirable in the interests of optimum clinical practice, and always possible since none of the relevant comparative images is missing1. • All images remain accessible from the PACS archives day and night, every day of the year. • Simultaneous multilocation viewing of the same image is possible on any workstation connected to the PACS network, whereas hard-copy film can manifestly only be in one place at any one time. • Image retrieval is infinitely quicker from PACS than it is using conventional film where someone physically has to go and fetch the film packet2. • The benefits of a computerized system mean that all images correctly and permanently reside under the appropriate









imaging study, remain in their correct orientation, and are automatically chronologically ordered. Database searches for a particular patient or study are rapidly effected. Computerized data can easily be duplicated, i.e. ‘backed up’ as a precaution against loss, and cheaply stored in a distant location if desired for disaster recovery purposes. Viewing of images on monitors allows numerous postprocessing soft-copy manipulations: a range of different window width and level settings can be applied to CT images, for example, within a fraction of a second, whereas previously further sheets of film had to be printed with the appropriate settings for soft tissue, lung or bone as desired3,4. There are some direct cost savings due to PACS: there is no longer a film budget, film packet cost or chemical processing. (The ability to print film need not be retained provided a CD burner is linked to the PACS to burn imaging studies for transfer of patients outside the institution, or in the event of a PACS failure or planned downtime). Ancillary staff – filing clerks and darkroom technicians – are no longer needed. The most frequently cited benefit of PACS by nonradiological clinicians is the very substantial time saving incurred by their never having to search for or retrieve films. This time saving represents a considerable indirect financial benefit of a hospital-wide PACS, and should certainly be costed when a business case for PACS is being made. After a hospital-wide PACS has been installed, old films can progressively be removed from the film filing room (film store) starting with the oldest first.The timing of this manoeuvre will depend upon local and national policy, but it has been shown5 that most radiological comparisons are made with studies obtained during the preceding 6 months, although this may be longer in institutions with a large oncological or paediatric practice. Maintenance of a film store, with its associated lighting, heating and cleaning, and the value of the physical space itself, is particularly costly in hospitals located in cities where the space is at a premium. Even off-site film storage at a cheaper location is worth introducing as a cost-saving measure in such institutions in the early years after PACS

CHAPTER 1



PICTURE ARCHIVING AND COMMUNICATION SYSTEMS (PACS) AND DIGITAL RADIOLOGY

has been installed, before the film store can be dispensed with altogether. (In the UK it is the radiological report, not the images that are deemed to be the legal document, with certain restrictions for paediatric and educationally challenged patients.) • The installation of a PACS infrastructure in an institution (a local area network [LAN]) sets the stage for the introduction of teleradiology over a wide area network (WAN) if desired. Teleradiology offers the potential for improvements in efficiency, for example in geographically remote areas by centralizing a reporting service, or increasing the referrals to a particular institution. A number of perceived potential benefits of PACS have not been substantiated, or not consistently demonstrated, by audit studies. These include the possibility of a reduced hospital inpatient stay or a greater throughput of outpatients6. It is hardly surprising that such benefits cannot be attributed to PACS since there are so many other variable factors that influence these issues. Also the type of study required to prove any given putative benefit of PACS is fraught with practical difficulties. The classical ‘before’ and ‘after’ study comparing the pre-PACS with the post-PACS era is inevitably complicated by the numerous other concurrent environmental, technological (and often political) changes that have taken place in the interim. These include, for example, changes in the medical personnel and in the type of clinical practice pursued in the hospital under study. Studies comparing a PACS institution with a nonPACS institution may be similarly flawed by the difficulty in adequately correcting for other inherent differences between the two institutions, which may or may not be related to the presence of a hospital-wide PACS7.

DISADVANTAGES OF PACS The advantages of PACS described earlier must be set against its potential disadvantages: • Even though the costs of hardware and storage media continue to reduce in price, PACS remains an expensive technology. Most estimates suggest that a PACS installation should aim at becoming cost-neutral in less than 5 years. Some would argue that PACS should be viewed in the same way as any new imaging technique, and as such it represents an advance in health care management and should not be assessed merely in terms of cost–benefit. • The technological complexity of a PACS and the absolute dependency of a hospital on the PACS once it becomes filmless require a dedicated maintenance programme for the PACS and a carefully devised plan detailing how to supply a minimal clinical service should the whole PACS fail for a significant period of time. This inevitably means that there will be a requirement for new or retrained hospital personnel specializing in computer engineering/information technology, as well as a vendor-provided maintenance service, and these costs must be set against the savings made in respect of less highly paid clerical staff and darkroom technicians. • Once a hospital-wide PACS is in operation and film has been withdrawn, there is no ‘fall-back position’. The hospital is no longer equipped to run a film-based service. This is a daunting prospect that may act as an initial psychological deterrent to embarking upon a large-scale PACS project. • Changing from a hard-copy to a soft-copy imaging environment will raise many issues necessitating a change of work patterns involving: the training of the users, maintenance of the system, action to be taken in the event of a PACS failure and the institution of specific quality assurance protocols (see later).

PLANNING FOR PACS THE PACS PROJECT TEAM The planning and installation of a PACS requires the coordinated input of a multidisciplinary team that might beneficially include representatives from the IT department, computer scientists, physicists, nonradiologist clinicians, radiologists, radiographers, nurses, hospital management, the hospital financial manager and, ultimately, a representative from the chosen PACS vendor. This emphasizes that PACS must have ‘buy in’ from the whole hospital/health care enterprise, and is not a ‘radiological toy’. The project team needs a leader with sufficient time to commit to the project8. This leader need not be a radiologist, or indeed a clinician, but must have a comprehensive practical grasp of the clinical workings of a hospital environment as well as an understanding of basic IT issues and the requirements of imaging.

TENDERING FOR A PACS When tendering for a PACS, a detailed request for tender/ proposal (RFT/RFP) will need to be drawn up9,10. This

document should define the clinical and logistical requirements of the PACS, rather than merely stipulating technical specifications. It is up to the radiologists and other clinicians to specify the current and projected future performance requirements that the PACS must fulfill (including the issues of PACS maintenance, uptime and data migration) and it is the role of the vendors to specify how these clinical requirements are to be met technically.

THE PACS CONTRACT Every PACS project should be based on a firm contract between the institution and the vendor, defining the responsibilities of each in detail. The PACS contract serves as a legal document and requires careful wording. Any subsequent changes or additions to the contract should be made as formal addenda ‘change control notices’ (CCNs) to the original contract, to preserve the legal integrity of the document. This also serves as an audit trail, keeping the contract up to date, and simplifying the situation for both purchaser and vendor.

5

6

SECTION 1

• IMAGING TECHNIQUES AND GENERAL ISSUES

It is important to define what is meant by ‘the life of the system’. This is often taken as being 8–10 years after the completion date.The majority of PACS installations are now based on some form of leasing agreement, rather than an outright capital purchase of the hardware and software. The date at which the maintenance contract will commence, its cost and its terms, all need careful definition. Responsibility must be defined for migration of the PACS archive data at the end of the PACS contract, or in the event of premature termination of the contract. It is advisable to define exactly what is meant by an ‘update’ to the system (generally a minor software release that merely corrects bugs in the system), and what is meant by an ‘upgrade’ (which constitutes a new software installation comprising major new features giving enhanced functionality), whether these are to be included in the purchase price/maintenance agreement, and at what frequency these will occur. An important consideration in negotiation with a vendor is the terms under which the delivered PACS hardware will be replaced if upgrades are released that it cannot support. It is vital to define which party is ultimately responsible for the functioning of the interfaces to the various pieces of imaging equipment, and to other hospital computer systems including the hospital and radiological information systems (HIS and RIS), electronic patient record (EPR), speech recognition dictation system, and electronic remote requesting (order communications) system, if these are already extant in the institution.

ECONOMIC CONSIDERATIONS The main reason for putting in a PACS (ultimately a hospital-wide or larger PACS) is to improve the efficiency of data handling throughout the whole of that health care environment. Much of the benefit will be experienced outside the imaging department itself, which is why PACS must be hospital driven (and funded), not radiology driven. PACS should be part of the hospital-wide information management and technology strategy, with the aim of achieving cost neutrality over about 3 years.

PURCHASING VERSUS LEASING A PACS The options for PACS procurement are broadly 2-fold11: 1 Capital purchase, using the hospital’s capital allowance, or 2 Some form of leasing arrangement. The fundamental difference between the two is that with capital purchase the hospital owns the assets (the PACS), whereas with any leased arrangement the hospital procures a service that contractually provides agreed functional outcomes (the output-based specification [OBS]). The vast majority of PACS installations nowadays are on a leasing scheme with a managed service provided by the PACS vendor. A leasing arrangement means that all the PACS equipment (hardware and software) is provided as a service from

a private company (with a maintenance contract). Nothing is owned by the hospital, i.e. the private company retains all the assets. The advantage of a leasing arrangement is that it allows hospitals with no hope of ever having the large capital sum necessary to purchase a hospital-wide PACS to make a quantum leap in technology to move to a PACS solution, and it transfers the risk to the company. It has to be appreciated, as with renting a house, that the hospital would be left with nothing if it were to stop paying the lease. At the end of the contractual term, the hospital does not own anything. However, in these circumstances the hospital is usually given an option to buy the installed assets (the PACS hardware and software) at ‘a fair market value’, as negotiated with the provider. In a leased service the PACS company provides the PACS hardware and software necessary to meet the workload and performance requirements stipulated by the hospital, both at the time of leasing and in the future. For example, such requirements might include the need to perform 400 000 imaging examinations per year, with a short-term storage of a year, and a display time for these examinations (first image to screen) of 3 s or less.The PACS company is responsible for maintaining a PACS with an agreed level of technology throughout the contractual term. The technological risk rests with the provider. The risk covers the following three areas: • Utilization of the system • Availability of the system to users • Future planning and implementation of new technology into the hospital’s system. The risk is transferred to the service provider by linking their revenues to agreed performance targets for the above. In addition the hospital should be provided with a guaranteed programme of equipment replacement and a guarantee to keep pace with technology. Leasing arrangements vary from about 8–30 years, with some planned ‘built-in’ equipment replacement ‘hardware swap-out’ at 5-yearly intervals, or 3–4-yearly technological reviews with ‘technology refreshments’ of software and/or hardware as may be necessary to provide greater productivity or capability. This technology refreshment may be a chargeable issue depending upon the contract and/or negotiations. Companies generally expect to recoup their capital outlay in approximately 3–5 years in a leased arrangement, but this will of course depend upon the financial model being used.

PRE-PACS WORKFLOW AND PREPARATION A number of careful and detailed preliminary pre-PACS studies of the workload and workflow pattern within the hospital/ health care facility will need to be conducted before the clinical requirements to be met by the PACS can be specified12.This includes documenting how many imaging examinations in each modality are performed annually, the average (and maximum) number of images per examination for each modality, and making a prediction of the rate of growth of the imaging workload.This prediction will be influenced by the expectation,

CHAPTER 1



PICTURE ARCHIVING AND COMMUNICATION SYSTEMS (PACS) AND DIGITAL RADIOLOGY

for example, of acquiring a new 64-slice (or greater) multidetector CT machine, the intention to start performing high image acquisition studies in MR such as cardiac or breast imaging and so forth. The predicted image storage requirement should always be an overestimate to allow for unexpected demand. It is also advisable to know which outpatient clinics are performed when, and how many film packets are pulled for each, to give some estimate of the network traffic to be expected. It is also important to define the role of the imaging department in other imaging-related activities, such as the radiological steps involved in conducting multidisciplinary team meetings (MDTMs) and radiological presentations at staff rounds, and undergraduate and postgraduate teaching sessions. PACS must be able to fulfill all these functions. The Imaging Directorate would be wise to know before PACS is installed, exactly how many imaging studies are never reported (for various reasons such as: the film packets are never returned to the department for reporting), the time between image examination acquisition and dictation of a report by a radiologist for each investigation and the time delay (if any) between dictation of the report and the availability of the verified report to other clinicians. These workflow deficiencies need to be addressed and corrected prior to the installation of a PACS, since the PACS will not ameliorate the situation but instead will expose these issues by making such information available in computerized form throughout the PACS institution. Seamless integration with other IT systems, and with imaging acquisition devices, is absolutely vital for a PACS to function successfully, and every modern PACS depends upon adherence to DICOM and HL7 standards and IHE (see next paragraph for an explanation of each) workflow processes to achieve this integration13. Before installing PACS, old equipment and old data information systems will need to be upgraded to a minimum level of DICOM and HL7 compliance, respectively. Often it is cheaper to replace such products with modern versions, rather than to pay to upgrade them. A full inventory must be made of the equipment and IT systems to be connected to the PACS with a precise description of the level (if any) of DICOM or HL7 compliance supported, before a PACS project can be properly planned and costed. The full DICOM conformance statement of every piece of DICOM-compliant equipment (e.g. a computed tomography [CT] scanner, an ultrasound [US] machine, a workstation etc.) is available on the Internet. It is generally the users’

responsibility to list the make and model of all the equipment possessed by the hospital/health care facility, and the PACS vendor’s responsibility to look up and interpret the DICOM conformance statements and to make it clear which pieces of equipment will need upgrading/replacing, and to explain the connectivity limitations if such DICOM upgrades are not undertaken. One of the major causes of interoperability problems when linking equipment from different vendors to a PACS is the use of ‘private DICOM attributes’ by many vendors, which, in simple terms, means that information stored in these particular private DICOM fields is not available to be shared with other apparatus, manufactured by a different vendor, which may be linked to it on a network. This leads to a loss of functionality on the recipient apparatus, for example not being able to post-process scanner images received on a workstation from a different vendor.

ACRONYMS: DICOM, HL7 AND IHE DICOM stands for digital communication in medicine and refers to a worldwide multipart standard to which all modern imaging equipment and PACS must adhere, and has now been extended to other disciplines, including cardiology, endoscopy, and ophthalmology. The DICOM conformance statement of every piece of modern imaging equipment is obligatorily available on the Internet, and the description of the various DICOM attributes possessed by each appliance will predict its connectivity with another piece of equipment. All apparatus is described as being a ‘user’ or a ‘provider’ of services such as storage.The DICOM standard is continuously under development, but each new part of the DICOM standard has to be backwardly compatible with the current DICOM standard. HL7 stands for health level 7 and refers to a worldwide standard for data information systems such as HIS and RIS. It is a less rigorous standard than DICOM. HL7 messages from data information systems are conveyed to DICOM apparatus (including PACS) by a ‘broker’, which acts as an integrating and translation device. IHE stands for integrating the health care enterprise and is not a standard, but a comprehensive workflow descriptor of how processes, such as reporting, for example, are achieved in imaging. Its use of integration profiles eliminates the need to reconcile the details of HL7 messages and DICOM conformance statements among multiple vendors. It is now being expanded outside the discipline of imaging.

PACS PROJECT IMPLEMENTATION The PACS project should be treated as a major IT project and divided into stages (milestones) with specific dates set for the completion of each stage. It may be useful in the UK to base the project management on the PRINCE guidelines published by the HMSO14 for major IT equipment contracts. Only after each consecutive milestone is satisfactorily completed and assessed is the next milestone embarked upon.

Each milestone requires conformance testing and clinical acceptance15. These are distinct entities: conformance testing should be carried out independently by hospital employees as well as by the vendor company itself. Payment is best deferred until after clinical acceptance at each stage. Final payment is only made after agreed satisfactory functioning of the system under loaded conditions, in a clinical setting.

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A realistic definition of the expected dates of completion of each milestone (including installation dates), with penalty clauses written into the contract to come into effect if these dates are overrun, protects the institution from major delays since penalties can be extracted from the vendor if such delays occur.

IMPLEMENTATION OF DIGITAL IMAGE ACQUISITION PRIOR TO PACS Plain radiography (chest, abdominal and skeletal plain images) still constitute the majority (usually 60 per cent) of imaging examinations in most general radiology departments. These examinations therefore need to be acquired in a digital format in order to be transferred to PACS. This represents a considerable challenge since conventional plain film work is still such a significant part of the total departmental workload. The other imaging investigations (computed tomography [CT], magnetic resonance [MR], nuclear medicine [NM], positron emission tomography [PET], US, digital subtraction angiography, and fluoroscopy) are either already digital in nature at acquisition or can be rendered so by screen capture/frame grabbing from the acquisition device, and can thus be easily transferred to PACS. There are three basic means of rendering plain radiographic images digital: 1 Digitizing conventional analogue film 2 Photostimulable phosphor plate technology, commonly known as computed radiography (CR). 3 Direct digital radiography. There is considerable new technology associated with acquiring plain radiographic images digitally, whichever method is chosen. In situations other than the opening of a new hospital/health care facility, it is circumspect not to introduce this new technology concurrently with a PACS to avoid the risk of ‘technology overload’ for the users. Once the bulk of the imaging studies (i.e. the plain radiography) is being acquired and stored digitally, the introduction of PACS and the complete withdrawal of film is a less daunting task. The overlap period, in which a digital archive is being built up whilst continuing to distribute film outside the imaging department, should be kept to a minimum for financial reasons: it is obviously expensive to run hard- and soft-copy systems concurrently. A period of 8 mm25. CTC outperforms double contrast barium enema (DCBE) in all studies. The clinical significance of ‘missed’ and diminutive polyps has also been questioned, given the slow progression of polyps over time26. Moreover, there is wide variation in the reporting of polyps even among ‘expert’ readers27, illustrating that this truly is a technique in evolution from a technical perspective, with a steep learning curve for the radiologist. Multicentre trials are currently underway in the USA (ACRIN) and the UK (SIGGAR 1) to evaluate the use of CTC in the context of a screening programme, but at present the majority view is that colonoscopy should be viewed as the gold standard, with CTC likely to replace the DCBE in the future. Again CAD techniques are under evaluation.

identifying the arterial and venous anatomy of the donor for surgical planning. Following transplantation, we have found MDCT to be particularly useful in evaluating the vascular supply to the graft in cases of suspected ischaemia where US is nondiagnostic (Fig. 4.7).

Genitourinary The evaluation of a patient presenting with haematuria may involve intravenous urography, ultrasound, CT or MRI in combination with cystoscopy. Increasingly, MDCT is being used as the primary imaging investigation as it has a high sensitivity for detecting malignant lesions, calculi and traumatic injuries. The other major causes (infection, coagulopathy, instrumentation) may be diagnosed on clinical history and blood and urine testing.The technique employed should encompass an unenhanced study (to detect calculi), a nephrographic phase (approximately 100 s, to assess the renal parenchyma) and an excretory phase (8–10 min, to assess the ureters). The latter two stages may be combined by giving the intravenous contrast medium in two parts, 8–10 min apart, and then imaging 100 s after the second dose. This will significantly reduce the radiation dose to the patient. As MDCT may not depict flat tumours of the bladder wall, cystoscopy must not be omitted. The increased anatomical resolution and multiplanar reconstructions possible with MDCT have enabled its use for surgical planning. In particular, urologists are able to accurately assess whether resection of a malignant lesion requires partial or complete nephrectomy, whilst potential organ donors may be noninvasively evaluated with an accurate depiction of the renal vasculature.

Paediatric Imaging children with CT poses a number of problems. It requires cooperation with instructions and the need to remain still, requires a high degree of spatial resolution to depict smaller organs and their vessels and exposes patients to a relatively high dose of radiation. Some hold that around 1 per

Hepatobiliary The use of multiple phases of contrast-enhanced imaging has probably had the greatest impact in liver imaging, which is reflected in the extensive US, CT and MR literature on the subject. The detection and characterization of focal liver lesions is largely based on patterns of vascular enhancement, with the hypervascular lesions—hepatocellular carcinoma (HCC), regenerative nodules, focal nodular hyperplasia and adenoma—in particular providing diagnostic dilemmas. In order to optimize contrast enhancement, our practice is to trigger the CT study from the arrival of contrast in the abdominal aorta. CT-based surveillance programmes for early detection of HCC with cirrhosis consist of an arterial and portal venous phase study at the very least, with many centres also obtaining unenhanced images. Both early and late arterial phase imaging can be performed, but no additional benefit for this has yet been shown. In living related liver transplantation, MDCT may be used to determine liver volumes and is increasingly utilized for

Figure 4.7 Coronal MIP image demonstrating hepatic artery thrombosis with collateral arteries in a patient following liver transplantation.

CHAPTER 4

1200–2000 patients undergoing CT might develop cancer because of the effects of the CT radiation, and these risks are greater in children28. Advances in MDCT have led to a significant reduction in acquisition time, which has been shown to reduce the need for sedation of paediatric patients29. Simultaneously, it has become possible to reduce the collimation below 1 mm, dramatically improving the resolution, and thereby not only aiding the diagnosis but also enabling accurate assessment of congenital abnormalities and surgical planning, particularly in patients with malignancy. Unlike in adult patients, imaging in different vascular phases is discouraged because of radiation issues. Therefore it is important to select a single optimal imaging sequence whenever possible (e.g. in a Wilms’ tumour, the late arterial phase will also opacify the renal veins and upper IVC). Optimizing an MDCT study for a paediatric patient should also include reducing the radiation dose as much as is possible while maintaining diagnostic quality. Reducing the kV and/or mAs will significantly reduce the dose to the patient30, and this can now be modulated automatically during imaging on newer machines, giving a constant image signal-to-noise ratio throughout the study. Additionally, increasing the pitch reduces the radiation dose significantly without loss of diagnostic quality30.

WHOLE BODY MDCT IN ASYMPTOMATIC ADULTS Whole body CT imaging of asymptomatic patients is controversial, yet is becoming commonplace in several countries, particularly the United States. Clearly, the potential benefits of identifying early stage malignant lesions or coronary heart disease with one noninvasive test could be enormous, but as yet the case for whole body CT screening is far from proven. When considering these studies, it should be borne in mind that a single CT examination cannot be optimized for looking at all organs at once. Consequently, the sensitivity and specificity of a whole-body study is likely to be significantly lower than with the dedicated organ-specific studies currently being evaluated. Inevitably, further follow-up investigations will be required for incidental findings, resulting in anxiety and distress for the patient and occasionally lead to morbidity and mortality. Moreover, the radiation dose is nontrivial. A recent publication exploring the hypothetical situation of a 45-year-old man undergoing annual screening CT until the age of 75 calculated the overall estimated lifetime attributable risk of cancer mortality to be approximately 1.9% (1 in 50)31. This combination of high cost, low specificity and high risk indicates that it is unlikely that whole body CT screening would be of benefit to the population. In the UK, such CT examinations are not recommended by the National Screening Committee32.

RADIATION DOSE CONSIDERATIONS In the late 1980s, CT represented approximately 2% of radiological investigations and 20% of the collective dose to the



MULTIDETECTOR COMPUTED TOMOGRAPHY

population. In 2003–2004, it is estimated that this has increased to 9%, with the dose from CT contributing around half of all radiation from medical exposures33. Since 1997, CT has been designated a high-dose procedure by the European Union, along with interventional radiology and radiotherapy. The reasons for this expansion in practice have been outlined above, with MDCT able to perform increasingly complex diagnostic procedures noninvasively and, in some instances, requiring multiple phases of imaging. Furthermore, unlike conventional plain radiography, where the radiation dose from each exposure is to some extent regulated by automatic detectors (increasing the dose will result in an overexposed, dark radiograph of little diagnostic value), increasing the exposure factors (and patient dose) for a CT study will provide the user with higher quality images. More difficult to assess is the effect that an increasingly litigious society has had on the practice of medicine and in particular the number of requests for studies ‘to rule out’ underlying tumour, pulmonary embolism, etc., even when these are clinically unlikely. The responsibility for reducing patient dose should be shouldered by all parties. The referring clinician should ensure that the radiologist is given full clinical information to ensure that CT is indeed the most appropriate test. The radiologist should ensure that each study is justified, that the imaging protocols are optimized to answer the clinical question and that the dose to the patient follows the ALARA (as low as reasonably achievable) principle. CT manufacturers also play a key role in this area through the continued development of dose modulation and the installation of low-dose preset protocols. In order to maximize patient safety, it is essential that all these issues are addressed in each case.

RADIOTHERAPY Over the past decade, significant advances have been made in the planning and delivery of radiotherapy. The introduction of MDCT enabled the oncologist to map the extent of tumour in three planes, allowing accurate dose planning of irregular shapes while minimizing the dose to the surrounding normal tissues. This 3D conformal radiotherapy (CRT) results in a significant reduction in side-effects. However, there were limitations in corrections that could be made to the delivered dose. More recently, intensity modulated radiotherapy (IMRT) has been developed, whereby each radiation beam is divided into 1-cm2 ‘beamlets’, each delivering a different prescribed dose. This has reduced even further the dose delivered to the surrounding normal tissues through increasing accuracy of delivery. Current research in radiotherapy includes the development of techniques to account for movement during radiotherapy, particularly respiration, with 4D CRT. Moreover, techniques are being developed which take account of the changes to the patient and tumour (weight loss and tumour shrinkage) that occur during a course of radiotherapy, so-called adaptive radiotherapy. It is anticipated that both of these will again further the accuracy of radiotherapy with more precise dose delivery and reduced side-effects. The increasing use of functional imaging of tumours with 18FDG-PET is also beginning to impact on

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radiotherapy planning. The co-registration of anatomical and physiological images using CT-PET has resulted in significant advances in lung tumour radiotherapy in particular, as it is now possible to differentiate between the central obstructing tumour and distal collapse.

10.

11.

FUTURE DIRECTIONS The gantry speeds and coverage currently achieved in MDCT are more than adequate for almost all clinical applications. The most notable exception, cardiac imaging, will undoubtedly drive manufacturers to produce yet faster machines with greater coverage until high-quality,‘real-time’ images are achieved, which could potentially directly replace all diagnostic coronary angiography. A significant improvement in resolution will be more difficult to achieve using the current technology with up to 64 banks of detectors.This would require significant improvements in detector efficiency and size reduction. However, the next generation of CT machines may instead employ flat panel detectors. Early reports of prototype machines indicate that spatial resolution is greatly improved, with isotropic voxels of the order of 0.25 mm, with coverage of approximately 20 cm in the z-axis per revolution. However, contrast resolution is relatively poor and data acquisition is still slow on these machines at present. One of the most important potential applications for such high-resolution studies, in addition to those described above, would be imaging of the breast. Early reports indicate that the technique is feasible at a dose comparable to that from 2-view mammography, with the added advantages of better tumour localization and potentially better detection of tumours. The tumour detection and dose characteristics will clearly be of greater importance than the speed of data acquisition for breast work, but increased speed will be crucial for cardiac applications.

REFERENCES 1. Ambrose J, Hounsfield G N 1973 Computerized transverse axial tomography. Br J Radiol 46: 148–149 2. Kalender W A, Seissler W, Klotz E, Vock P 1990 Spiral volumetric CT with single-breath-hold technique, continuous transport, and continuous scanner rotation. Radiology 176: 181–183 3. Tipper G, U-King-Im J M, Price S J et al 2005 Detection and evaluation of intracranial aneurysms with 16-row multislice CT angiography. Clin Radiol 60: 565–572 4. Matsumoto M, Kodama N, Sakuma J et al 2005 3D-CT arteriography and 3D-CT venography: the separate demonstration of arterial-phase and venous-phase on 3D-CT angiography in a single procedure. Am J Neuroradiol 26: 635–641 5. Miles K A, Hayball M, Dixon A K 1991 Colour perfusion imaging: a new application of computed tomography. Lancet 337: 643–645 6. Gillard J H, Minhas P, Hayball M P et al 2000 Evaluation of quantitative computed tomographic cerebral perfusion imaging with H215O positron emission tomography. Neurol Res 22: 457–464 7. Wintermark M, Fischbein N J, Smith W S, Ko N U, Quist M, Dillon W P 2005 Accuracy of dynamic perfusion CT with deconvolution in detecting acute hemispheric stroke. Am J Neuroradiol 26: 104–112 8. Wintermark M, van Melle G, Schnyder P et al 2004 Admission perfusion CT: prognostic value in patients with severe head trauma. Radiology 232: 211–220 9. O’Rourke R A, Brundage B H, Froelicher V F et al 2000 American College of Cardiology/American Heart Association Expert Consensus document

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on electron-beam computed tomography for the diagnosis and prognosis of coronary artery disease. Circulation 102: 126–140 Nieman K, Cademartiri F, Lemos P A, Raaijmakers R, Pattynama P M, de Feyter P J 2002 Reliable noninvasive coronary angiography with fast submillimeter multislice spiral computed tomography. Circulation 106: 2051–2054 Ropers D, Baum U, Pohle K et al 2003 Detection of coronary artery stenoses with thin-slice multi-detector row spiral computed tomography and multiplanar reconstruction. Circulation 107: 664–666 Schuijf J D, Bax J J, Salm L P et al 2005 Noninvasive coronary imaging and assessment of left ventricular function using 16-slice computed tomography. Am J Cardiol 95: 571–574 Cademartiri F, Mollet N R, Runza G et al 2006 Diagnostic accuracy of multislice computed tomography coronary angiography is improved at low heart rates. Int J Cardiovasc Imaging 22: 101–105; discussion 107–109 Cross J J L, Kemp P M, Walsh C G, Flower C D R, Dixon A K 1998 A randomized trial of spiral CT and ventilation perfusion scintigraphy for the diagnosis of pulmonary embolism. Clin Radiol 53: 177–182 O’Neill J, Murchison J T, Wright L, Williams J 2005 Effect of the introduction of helical CT on radiation dose in the investigation of pulmonary embolism. Br J Radiol 78: 46–50 Quiroz R, Kucher N, Zou K H et al 2005 Clinical validity of a negative computed tomography scan in patients with suspected pulmonary embolism: a systematic review. JAMA 293: 2012–2017 Prologo J D, Gilkeson R C, Diaz M, Cummings M 2005 The effect of single-detector CT versus MDCT on clinical outcomes in patients with suspected acute pulmonary embolism and negative results on CT pulmonary angiography. Am J Roentgenol 184: 1231–1235 Cham M D, Yankelevitz D F, Henschke C I 2005 Thromboembolic disease detection at indirect CT venography versus CT pulmonary angiography. Radiology 234: 591–594 Tins B J, Cassar-Pullicino V N 2004 Imaging of acute cervical spine injuries: review and outlook. Clin Radiol 59: 865–880 Brohi K, Healy M, Fotheringham T et al 2005 Helical computed tomographic scanning for the evaluation of the cervical spine in the unconscious, intubated trauma patient. J Trauma 58: 897–901 Griffen M M, Frykberg E R, Kerwin A J et al 2003 Radiographic clearance of blunt cervical spine injury: plain radiograph or computed tomography scan? J Trauma 55: 222–226 Elton C, Riaz A A, Young N, Schamschula R, Papadopoulos B, Malka V 2005 Accuracy of computed tomography in the detection of blunt bowel and mesenteric injuries. Br J Surg 92: 1024–1028 Taylor S A, Halligan S, Bartram C I et al 2003 Multi-detector row CT colonography: effect of collimation, pitch, and orientation on polyp detection in a human colectomy specimen. Radiology 229: 1–2 Rockey D C, Paulson E, Niedzwiecki D et al 2005 Analysis of air contrast barium enema, computed tomographic colonography, and colonoscopy: prospective comparison. Lancet 365: 305–311 Pickhardt P J, Choi J R, Hwang I et al 2003 Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med 349: 2191–2200 Macari M, Bini E J, Jacobs S L et al 2004 Significance of missed polyps at CT colonography. Am J Roentgenol 183: 127–134 Johnson C D, Harmsen W S, Wilson L A et al 2003 Prospective blinded evaluation of computed tomographic colonography for screen detection of colorectal polyps. Gastroenterology 125: 311–319 Brenner D J, Elliston C D, Hall E J, Berdon W E 2001 Estimated risks of radiation-induced fatal cancer from pediatric CT. Am J Roentgenol 176: 289–296 Pappas J N, Donnelly L F, Frush D P 2000 Reduced frequency of sedation of young children with multisection helical CT. Radiology 215: 897–899 Donnelly L F, Emery K H, Brody A S et al 2001 Minimizing radiation dose for pediatric body applications of single-detector helical CT: strategies at a large children’s hospital. Am J Roentgenol 176: 303–306 Brenner D J, Elliston C D 2004 Estimated radiation risks potentially associated with full-body CT screening. Radiology 232: 735–738 Dixon A K 2004 Whole-body CT health screening. Br J Radiol 77: 370–371 Shrimpton P C, Hillier M C, Lewis M A, Dunn M 2005 Doses from computed tomography (CT) examinations in the UK—2003 review. National Radiation Protection Board, Oxon, UK

CHAPTER

Magnetic Resonance Imaging: Basic Principles

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• • • • • • • • •

Historical perspective Spin physics Excitation and relaxation: free induction decay and echoes Signal localization: techniques for building images Instrumentation: magnets, coils and computers Physical parameters that provide contrast Pulse sequences Safety considerations Conclusion

This chapter considers the basic principles of the MRI technique. Magnetic resonance imaging (MRI) is a noninvasive method of mapping the internal structure and certain aspects of function within the body. It uses nonionizing electromagnetic radiation and appears to be without exposure-related hazard. It employs radiofrequency (rf) radiation in the presence of carefully controlled magnetic fields in order to produce high quality cross-sectional images of the body in any plane. It portrays the distribution of hydrogen nuclei and parameters relating to their physical surroundings in water and lipids. MRI has progressed over 30 years from being a technique with great potential to one that has become the primary diagnostic investigation for many clinical problems. Its application, initially limited to the neuro-axis, now covers all regions of the body and an increased knowledge base has provided a better understanding of how it can best be utilized, either alone or in conjunction with other techniques, in order to maximize diagnostic certainty. Technical advances have included improvements in spatial resolution, types of contrast and, in particular, speed of imaging. The range of information that can be obtained from a multitude of different types of image contrast is one of its biggest selling points: modern MR is truly multimodal, capable of depicting function as well as anatomy with a high sensitivity to the presence of disease.

HISTORICAL PERSPECTIVE The phenomenon of ‘nuclear induction’, later to be termed nuclear magnetic resonance (NMR), was described independently but almost simultaneously by Bloch1 and Purcell2 and their colleagues in 1946 and for this they were jointly awarded the Nobel Prize for Physics in 1952. Much later, for some reason the term ‘nuclear’ was dropped. In applications to medicine, it is now commonly referred to as magnetic resonance (MR). Since its discovery, NMR has been used extensively as a laboratory method for studying the properties of matter at the molecular level (NMR spectroscopy). In 1971, Damadian noted that in vitro, animal tumours had elevated MR relaxation times when compared to normal control tissue, and in the following year he filed a US patent: ‘apparatus and method for detecting cancer in tissue’. The application of MR to imaging required a method of spatial localization. Published in 19733, Lauterbur’s paper showed how this could be done by applying a linearly varying magnetic field across a liquid. In the same year, Mansfield and Grannell reported revealing structure within a solid by the use of a linear magnetic field gradient4. Human in vivo images were first published in 1977 by Mansfield and Maudsley5, Damadian et al6 and Hinshaw et al7. Multiplanar imaging ability was first demonstrated by Hawkes et al in 1980, who also reported the first demonstration of intracranial lesions8, and 1980 also saw the introduction of the basis of the most common spatial encoding method – spin-warp imaging by Edelstein et al9.The introduction and subsequent improvements in diffusion, perfusion, flow and spectroscopy from a large number of groups have been providing fascinating new insights into cerebral and cardiac pathology10–16. Functional MRI (fMRI) of the brain, which uses endogenous blood oxygen level dependent (BOLD) contrast, was introduced by Ogawa et al in 199217 and developed by Rosen et al18. Methods have been developed that have enabled areas that have previously been difficult to assess, such as pulmonary ventilation, to be imaged with the aid

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of hyperpolarized helium gas19. New parallel encoding methods used with phased-array rf coils, such as SMASH introduced by Sodickson et al in 199720 and SENSE introduced by Pruessmann et al in 199921, are changing the rules of imaging speed, particularly when coupled with the introduction of 3T whole-body systems.

SPIN PHYSICS MR describes the phenomenon whereby the nuclei of certain atoms, when placed in a magnetic field, absorb and emit energy of a specific or resonant frequency. Nuclei suitable for MR are those which have an odd number of protons or neutrons and therefore possess a net charge distribution. They also exhibit the property of nuclear spin, which gives them angular momentum. The combination of charge and angular momentum causes these nuclei to behave as magnetic dipoles. Almost all medical images produced to date have used the simplest of all nuclei, that of hydrogen (a single proton), which is present in virtually all biological material and exhibits relatively high MR sensitivity. Other relevant naturally occurring nuclei include phosphorus (31P), sodium (23Na), carbon (13C) and potassium (39K). Noble gases such as helium (3He) and xenon (129Xe) can also be made sufficiently sensitive by laser pre-polarization techniques. The proton can be regarded as a small, freely suspended bar magnet spinning rapidly about its magnetic axis. Place a group of protons in a uniform magnetic field and their magnetic moments experience a torque, tending to line them up with the applied field. Due to thermal energy not all of the spins line up and at body temperatures the difference in numbers between those that do and those that do not (the net magnetization) is small. The stronger the applied magnetic field, the larger the net magnetization and the higher the available MR signal.The direction of the applied magnetic field conventionally defines the z-axis, which is generally in the craniocaudal direction in the common cylindrical imaging magnet configuration. Because the nuclei are spinning, they respond to the magnetic torque like a gyroscope and their axes are tilted so they rotate about the magnetic field’s axis in a movement termed ‘precession’. The frequency of precession is directly proportional to the applied magnetic field. For protons in a field of 3T, it is almost 128 MHz. This relationship is expressed by the Larmor equation: f0 = γB0 where f0 is the resonant frequency, γ is the gyromagnetic ratio (constant for a nuclear species) and B0 is the applied magnetic field.

EXCITATION AND RELAXATION: FREE INDUCTION DECAY AND ECHOES If rf energy is then applied, there is a strong interaction or resonant effect, providing that the frequency of the rf is equal

to the proton precession frequency. This is called magnetic resonance (MR) and manifests itself in the following way: rf energy is absorbed by the nuclei causing the motion of the nuclear dipoles to be disturbed (they become ‘excited’). Their net magnetization along the z-axis deviates through an angle that depends upon the amount of rf energy absorbed. Once the applied rf is turned off, the magnetization gradually returns to its equilibrium position. As it does so, the changing magnetization induces a small voltage in a receiver coil. In its simplest form, the electrical signal detected following an rf pulse is known as the free induction decay (FID), the size and length of which is determined by the sample’s proton density and relaxation times. The time it takes for the net magnetization to revert back to its equilibrium position along the longitudinal z-axis is governed by the longitudinal or T1 relaxation time. In this way, energy is given up by the spins to the overall structure or lattice (T1 can be called the spin–lattice relaxation time) and once the energy associated with a given excitation pulse has decayed away by this mechanism, it cannot be retrieved: you have to start again by applying another rf excitation pulse, imparting more energy to the system. In addition to the transfer of energy to the overall structure, the spins interact with each other. As this occurs, their net magnetization in the x–y plane (perpendicular to the z-axis) becomes less coherent or dephases. The rate at which it does so is governed by T2, the transverse or spin–spin relaxation time. As will be described below, for a given rf excitation pulse, part of the T2 decay or dephasing can be reversed, leading to the production of echoes. Due to the different nature of T1 and T2 decay, T2 can never be longer than T1. In liquids, T2 starts to approach the value of T1 and in human tissue, T2 is approximately a tenth of T1.The spin–spin interaction (T2 decay) can be hastened by the presence of local changes in magnetic field homogeneity. When this occurs, the transverse magnetization decays with time constant T2*, which is shorter than its intrinsic T2. So far, the production of a FID has been described, occurring after termination of an rf excitation pulse.To facilitate the spatial encoding process and to enable ‘weighting’ of the signal by various contrast mechanisms in differing proportions, it is necessary to delay the production of the signal. Within the overall decay envelope given by T2 relaxation, a signal echo (or echoes) can be formed in different ways. The two most common types of echo are the spin echo and the gradient echo (or field echo) (Fig. 5.1). Both cause rephasing or refocusing of the transverse magnetization (in the x–y plane) at an echo time (TE) following the excitation pulse. Spin echoes are produced by an 180-degree, second rf pulse which flips the spins over in the x–y plane: instead of spreading further apart, they refocus, moving into phase with each other again, pass through a maximum and then dephase once more. Gradient echoes are, as the name suggests, produced by the introduction of a magnetic field gradient: the gradient causes the spins to realign in the x–y plane while they are ‘pointing’ in the same direction (i.e. without flipping them over). At sufficiently long TE, spin echoes and gradient echoes produce signals that are

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90 rf

A

FID

Echoes

180 rf

B

SR

G

C

GE TE

Figure 5.1 Schematic depiction of signal formation: (A) application of a 90-degree rf pulse leads to the production of the free induction decay (FID); (B) a spin echo (SE) is produced at the echo time (TE) by the application of a 180-degree rf pulse at TE/2; (C) a gradient echo (GE) is produced by the application of a magnetic field gradient (G).

T2-weighted and T2*-weighted, respectively; that is, different tissues having different T2 and T2* relaxation times yield different signals that depend on the values of those relaxation times. There are other echo types: Hahn (or partial) echoes and stimulated echoes. The former will be briefly mentioned in the section outlining gradient-echo sequences.

SIGNAL LOCALIZATION: TECHNIQUES FOR BUILDING IMAGES The physical relationship that makes building up an image possible is the proportional relationship of the resonant frequency to the strength of the magnetic field (Larmor equation again). In understanding the MR spatial-encoding process, two concepts need to be separated: that of resonant frequency (as given by the Larmor equation: spins precessing at a high resonant frequency when in a high magnetic field) and spatial frequency (the high spatial frequency components of an image corresponding to the fine detail in that image). Imaging is performed using the properties of the Larmor relationship but, in addition to this, the data are encoded in the spatial frequency domain! The latter refers to the sampled signal being in the wonderful world of k-space. Different gradient schemes have been devised to traject through k-space in different ways but most images are acquired using a two-dimentional (2D) encoding technique which samples kspace as a set of rectangular Cartesian coordinates (like the regular spacing in a tight climbing net). The beauty of this method is that the image is then just the 2D Fourier transform of the sampled signal (Fig. 5.2). The basic components of this strategy can be split into three parts: 1 Slice selection is performed during the rf excitation process. The excitation pulse consists of a narrow bandwidth of frequencies. A linearly increasing field (field gradient) is applied across the object in the slice-select direction; the combination of the limited excitation bandwidth in the

Figure 5.2 (A) Two-dimensional (2D) ‘k-space’ magnitude data array and (B) corresponding sagittal T1-weighted proton density image formed after 2D Fourier transformation.

presence of the gradient means that only spins within a finite distance in the slice-encode direction (i.e. a 2D slice) will resonate and be excited. The slice position and thickness can be altered by adjusting the rf centre frequency, pulse bandwidth and/or gradient strength (rate of change of magnetic field across the object). A negative gradient lobe is added after excitation so that once slice selection has been accomplished, the spins across the chosen slice precess in-phase with one another. 2 Phase encoding is performed following excitation and prior to the formation of the signal echo. A second gradient is applied along one direction within the plane of the excited slice. While it is on, the presence of the gradient causes a linear change in spin precession frequency along its direction. As with slice selection, once it has been switched off, all spins within the slice revert to precessing at the static field’s resonance frequency. However, the phase-encoding gradient will have introduced an incremental phase shift along its direction, the size of which depends upon its magnitude. This corresponds to one sampled spatial frequency (one value of ky) along the phase-encode direction. In order

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to sample other spatial frequencies in that direction, the excitation process is repeated to fill the desired matrix size. During each repeat, which occurs every repeat time (TR), the strength of the phase-encode gradient is altered, so that a different phase shift is introduced, thereby encoding a different spatial frequency in the phase-encode direction. 3 Frequency encoding is performed during data sampling of the signal echo. A third linear field gradient is applied in the imaging plane, perpendicular to the phase-encode and slice-selection directions. At different positions along the frequency-encoding direction, spins will be resonating at different resonant frequencies as the signal is sampled. As the echo evolves, successive spatial frequencies of the object are encoded along this third dimension. Thus, in a basic spin-echo or gradient-echo technique (Fig. 5.3), during any one TR, the slice is selected, the total number of spatial frequencies (say 256 or 512) is sampled along the frequency-encode direction at one spatial frequency along the phase-encode direction. This process is repeated for the total number of spatial frequencies required in the phase-encode direction (say 256 or 512). This can lead to inappropriate, excessive imaging times if high spatial resolution is required (> 25 min for 512 phase encodes with a TR of 3 s). However, developments in sequence design have enabled multiple phase-encoding steps to be performed within each TR, speeding up the process using, for example, fast spin-echo (FSE) techniques (Fig. 5.4). It is important to realize that individual elements in k-space do not correspond on a one-to-one basis with individual pixels in the final image, but rather that each k-space element contains information about that spatial frequency component throughout the image. An alternative method to slice selection is to use an additional (secondary) phase-encoding gradient along the slice selection axis, yielding true three-dimensional (3D)-encoded datasets that typically have high spatial resolution in all three directions (often submillimeter). Putting together phase and frequency encoding plus slice selection has introduced the concept of a pulse sequence that consists of a series of applied rf and gradient pulses that lead to

TR 90

90

RF Slice Phase Frequency TE Signal

Figure 5.3 Basis of the gradient-echo (spin-warp) pulse sequence. Three orthogonal gradients are used for: slice selection (while the rf excitation pulse is applied); phase encoding (the amplitude of which is iterated every repeat time [TR]) and frequency encoding (leads to echo formation at the echo time [TE]). The process is repeated after time TR for the total number of required phase-encoding steps.

RF

90 

180 

180 

TR

180 

90  etc

Phase train

Figure 5.4 Train of 180-degree refocusing rf pulses that form the basis of the fast spin-echo (FSE) sequence. Each 180-degree rf pulse has a different magnitude phase-encoding gradient. A whole train of 2, 4, 8, etc. echoes are produced per TR, reducing the number of TRs required for a given total number of phase-encoding steps.

the production of the signal in the form of an echo which has been encoded in k-space.Variations in the timing of the component parts of these pulse sequences can be used dramatically to alter image contrast; this being one of the major advantages of MR, helping to identify anatomy and characterize normal and pathological tissue types. Adjustments to the building blocks and parameters that define a pulse sequence can be used to manipulate image contrast. Most sequences in use today are based on variants of the above. There are several other methods of moving or trajecting through k-space that have potential advantages. Of these, the most commonly used is echo-planar imaging (EPI). EPI was one of the first imaging schemes to be proposed. It requires very rapid gradient switching and is thus technically demanding and, in its early forms, prone to various artefactual complications (such as Eddy current effects). Technical developments have enabled its introduction on commercial clinical systems over the last 10 years. Its speed is a great asset, being capable of yielding an image in under 100 ms, and has led to its use in areas such as imaging of water diffusion and brain function. It is important to note that MRI is a true digital imaging technique as discrete data points are sampled which, when transformed, form an image made up of 2D picture elements (pixels) or 3D volume elements (voxels).

INSTRUMENTATION: MAGNETS, COILS AND COMPUTERS The major parts of an imaging system comprise (A) the magnet subsystem to produce a spatially and temporally constant B0; (B) the gradient subsystem to produce time-varying magnetic field gradients primarily for spatial encoding; (C) the rf subsystem to transmit and receive the rf energy; and (D) the associated microprocessors/computers to specify and control the pulse sequence, calculate, process, display, store and transfer the resultant images. The magnet, gradient and rf coils are all situated within an rf-shielded examination or magnet room. This shielding (a Faraday cage) consists of a conductive metal lining (copper or aluminium) through which rf electromagnetic radiation will not pass. It serves to keep external electrical noise out and the generated rf energy within the examination room. All electrical connections into the room must be filtered appropriately as they pass through this shield. Most screened rooms possess wave guides or tubes (with a high length-to-diameter ratio; > 5:1) fixed into the wall of the

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screened room, through which nonconductive tubing may be passed (plastic gas tubing or fibre-optic cabling).The examination room door should be shut while acquiring data to enable the shield to work effectively.

Static magnetic field (Fig. 5.5) Although it is possible to perform MR experiments within the earth’s magnetic field (being approximately 0.00004T!), most clinical MRI systems are constructed around magnets which produce fields in the range 0.2–3T. Research systems capable of human in vivo imaging at 8T and above are available. There has been much debate over the optimum B0 for clinical imaging and this debate continues.The vast majority of installed systems operate at 1.5T, although there is presently a surge in systems operating at the new high-field strength of 3T. Low-field, reduced cost systems (0.2–0.5T) are often marketed for various ‘niche’ applications (e.g. musculoskeletal extremity imaging). At this low end of the range, permanent ferromagnetic composites or room temperature electromagnets tend to be utilized. Above 0.5T, superconducting windings (a niobium–tin alloy embedded in a copper matrix) are supercooled in a bath of liquid helium (at 4.2 K or −269°C) such that they offer zero resistance to the high currents required to produce high magnetic flux densities. Superconducting magnets, which are constantly ‘on’ or ‘at field’, are mostly cylindrical in geometry, especially at 1.5T and above, although more ‘open’ designs are becoming available at 1T and below. Developments in magnet technology have meant that, provided the helium refrigeration pump remains in operation (usually a rhythmical thud can be heard while the system is not acquiring data), one fill of liquid helium should last several years. The overall size of these superconducting magnet systems has decreased substantially in recent years, yielding friendlier designs with reduced levels of patient anxiety/claustrophobia. Why buy a high B0 system? The protons’ net magnetization increases with B0, leading to an overall increase in imaging signalto-noise ratio (approximately a linear relationship). Various other parameters also change with increasing B0, leading to



MAGNETIC RESONANCE IMAGING: BASIC PRINCIPLES

potential benefits such as increased magnetic susceptibility contrast (useful for depicting nuclei within the brainstem or fMRI responses), greater resolution between resonance peaks in spectroscopy (potentially helpful for water/fat imaging) and an increase in tissue T1s (prolonged blood signal and better background suppression for time-of-flight angiography). However, higher is not automatically better as the aforementioned can also produce increased metallic foreign-body artefact, increased chemical shift artifact and changed T1 contrast. At high resonant frequencies, rf homogeneity also provides greater technical challenges. A high degree of homogeneity of the main magnetic field together with gradient linearity are essential for correct geometrical representation, this being especially pertinent when MR is used directly for therapy (e.g. in stereotactic radiosurgery to the trigeminal nerve or the placement of deep-brain stimulators). To maximize B0 homogeneity, a combination of passive and active shimming is employed. The former can take the form of a series of metallic coin-like discs or nougats, the configuration of which is usually site specific, determined and placed during installation. In high-end systems, active shimming can be computer optimized on each imaging volume for each patient episode.

Magnetic field gradients In cylindrical systems, the gradient coil sets required to produce the three orthogonal, linear gradient fields (gradients), are located adjacent to the inner surface of the magnet cryostat. The maximum gradient amplitude that can be generated (given in milliTesla per metre) has a significant effect on the minimum slice thickness and field of view and, thereby, the highest spatial resolution that can be achieved. The rate at which the gradients can achieve the desired amplitude is known as the gradient slew rate (given in milliTesla per metre per second). This sets a limit to the minimum TR and TE values that can be achieved, and thereby the minimum scan acquisition time. Applications such as fast cardiac, MR-digital subtraction angiography (MR-DSA), or high sensitivity diffusion tensor imaging require high amplitude gradients with a

Figure 5.5 MRI systems: (A) Modern system based on a cylindrical cryogenic magnet; (B) open magnet for interventional MRI; (C) low-field system for niche applications.

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fast slew rate. Fast gradient switching can lead to the induction of artefact-producing eddy currents within the conductive structures of the system. Improvements in gradient coil design and compensation methodology have significantly reduced this problem, although correct set-up during installation is essential for artefact-free use of gradient-intensive sequences such as echo-planar diffusion or sensitive techniques such as gradient localized spectroscopy. Powerful gradient amplifiers are an essential component of the gradient subsystem and are sited in a room with restricted access, adjacent to the magnet room.

Radiofrequency field Many of the rf transmit and receive subsystem components (digital-to-analogue converters, frequency mixers, power amplifiers, analogue-to-digital converters, etc.) are also sited within the electronics/cabinet room. These comprise all but the rf coils and associated receiver pre-amplifiers, which are placed close to the anatomical area under investigation in order to maximize their effectiveness. A typical system will have been purchased with a number of signal-detecting rf ‘receive’ coils, each dedicated to investigating a particular anatomical area (Fig. 5.6); often used in conjunction with the main rf transmitter body coil located adjacent to the gradient coil sets. The body coil is designed to provide a homogeneous rf excitation field throughout the required imaging volume. Many of the receiver coils will comprise several coil ‘elements’. Coil sensitivity needs to be maximized and the best signal-to-noise ratio can be obtained from a small volume adjacent to a close

fitting coil, but small coils only detect from a limited volume. To achieve high sensitivity over a large volume or area, several coil elements can be used in ‘phased-array’ configurations (e.g. for imaging the entire length of the spinal cord) or signals from multiple coils themselves (e.g. a coil ‘matrix’ covering the whole body) can be used in tandem.To facilitate this multicoil technology, many rf channels are used to pipe the detected signals away from the examination room. Thirty-two channel systems are available as standard product while those under research development can contain over 100. The number of coils/elements used is likely to grow substantially over the next few years. In addition to signal-to-noise ratio considerations, the inherent spatial information provided by arrays of coils/elements can be put to good use in parallel imaging techniques, where SENSE and SMASH technology can reduce the number of required phase-encoding steps and hence imaging time to yield a prescribed resolution. This is particularly pertinent to high-field strength systems where there is sufficient signal-to-noise ratio.

Pulse sequence control, data manipulation and image handling MR depends on highly sophisticated computing. The relentless increase in computing power has had a direct beneficial effect upon performance. Real-time image reconstruction is common without noticeable delay following data acquisition, which is important when hundreds (e.g. tissue perfusion studies) or thousands of images (e.g. BOLD fMRI studies) are acquired during a single examination. It is also now possible to

Figure 5.6 Examples of dedicated rf receive coils: (A) ‘CTL’ phased-array coil for imaging the whole spine plus typical anatomical coverage (B).

Continued

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Figure 5.6 cont’d (C) a neurovascular coil that allows MR angiography from the circle of Willis to the aortic arch (D); (E) a dedicated wrist coil designed to produce high-resolution imaging of the wrist joint (F).

register two or more datasets accurately with each other using complex computationally intensive algorithms. Slice positions can be prescribed automatically using such image registration techniques. Highly accurate comparisons between images from the same examination can be obtained ‘on the fly’ (e.g. statistical analysis of BOLD fMRI data) or from different examinations (e.g. subtraction of images to determine parenchymal volume changes in dementia or slowly evolving lesions such as meningioma). The real-time manipulation of 3D datasets (maximum intensity projections, surface rendering or general multiplanar reformatting) enables complex interactive postacquisition viewing strategies to be employed by the radiologist, which is particularly important when assessing complex vascular structures such as arteriovenous malformations or visualizing intracranial cortical developmental malformations. Digital data processing speeds will become even more critical if

ultra-high resolution imaging at very high field strengths (≥ 3T) with acquisition matrices of at least 2048 × 2048 becomes widespread. The common PC–user interface can be found on the majority of new MR systems. The introduction of picture archiving and communications systems (PACS) and the data standard, DICOM, has been evident. Local archive is still possible (commonly to DVD in new systems), but the provision of a central PACS archive is often assumed. The introduction of soft copy reviewing and reporting has meant that the radiologist is no longer confronted with fixed viewing parameters on sheets of film, but has the advantage of being able to interact with window widths and levels during the review process, enabling the interrogation of features that may be outside the acuity of the human visual system when observed on hard copy format. The incorporation of a plethora of functional investigative techniques into clinical practice (perfusion,

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exogenous contrast medium uptake, water diffusion, etc., and not just BOLD fMRI) often benefits from representation in colour overplayed on high resolution anatomical images. The rapid cinematic presentation of multiple contiguous sections can facilitate integration of information across several sections. Ciné presentations are frequently used in the analysis of dynamic studies, particularly of the vasculature.

PHYSICAL PARAMETERS THAT PROVIDE CONTRAST MR offers a vast range of possible image contrasts (Fig. 5.7), which, in turn, provides high sensitivity about the presence of many abnormalities. However, pixel values do not represent an absolute measure (e.g. absolute T2, in milliseconds). They are only absolute on the rare occasions when specialist quantitative techniques are invoked (e.g. calculation of absolute T2 of the hippocampal structures for the definition and lateralization of sclerosis in temporal lobe epilepsy). Rather, they reflect various physical parameters, including proton density, T1, and T2, and their scaling is influenced by factors such as body size (which affects rf coil loading and hence the induced voltage in the receiver coil). This is unlike CT, where pixel values in Hounsfield units correspond directly to X-ray attenuation (electron cloud density). When a particular physical parameter, e.g. the spin–spin relaxation time T2, dominates the relative pixel intensities in the image (i.e. the image contrast mostly reflects differences in T2), that image is said to be T2 weighted. The diversity of available weightings can lead to difficulties assessing what is the optimum amount of information to gather. As well as in-depth anatomical knowledge, interpretation requires knowledge regarding the type of weighting present in an image, how that relates to a particular physical contrast mechanism and how that contrast varies in the normal population and with disease. This section outlines the most common contrast mechanisms in common clinical use and emphasizes how they can manifest as artefacts or false image information if not properly analysed. Some examples are given.

Proton density It seems intuitive that the proton density (PD or ρ) of an object will fundamentally be linked to the size of the signal returned by that object. Indeed, this is the case; the higher the number of ‘MR visible’ protons, the greater the potential signal becomes. To provide image weighting so that the PD dominates pixel intensity, the effects of other potential influences should be minimized. This approach to providing the majority weighting by one factor is common practice in sequence design and protocol implementation (see ‘sequence’ section below). It is useful to rank body components according to their relative PDs. Highest are cerebrospinal fluid (CSF) and other fluids. These are followed in order by various soft tissues such as liver, kidney, spleen, grey matter and white matter, then articular cartilage, fibrocartilage, membranes, cortical bone and, lowest of all, air. It is important to recognize that the ‘MR visible’ proton pool consists of mobile protons. Hydrogen nuclei that form part of large molecular structures or are immobilized in solids have tight chemical bonds that ensure that they interact with each other so rapidly (i.e. have very short T2 values) that they provide no detectable signal over the timescales involved in standard clinical MR technique, and appear to have a PD of zero. PD is increased in some lesions.These include oedema, infection, inflammation, acute demyelination, acute haemorrhage, various tumours and cysts. Since the formation of oedema is a common response to a wide variety of insults, an increase in PD is a frequent occurrence. A decrease in PD may be seen in scar formation, fibrosis, some tumours, capsule and membrane formation, as well as with calcification. The changes in PD are often relatively small in comparison to the changes seen on T2-weighted images.

T1 (longitudinal relaxation time or spin–lattice relaxation time) This time constant characterizes the rate of the protons’ recovery from their excited state to their resting or equilibrium state, in the longitudinal or z-direction (parallel to the main field), for each component of the object. It relates to the transfer of energy from the protons to the tissue’s overall structure. Body

Figure 5.7 Patient with multiple sclerosis with plaques of demyelination shown on (A) fast spin-echo (FSE) proton density; (B) FSE T2; and (C) FSE FLAIR. There is no discernible abnormality on T1-weighted images without contrast medium (D).

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fluid T1 is long (typically 1500–2500 ms) compared to soft tissues (typically 300-1200 ms), while those of fatty structures are shorter still (100–150 ms). T1 increases with B0, requiring an alteration in sequence parameters to provide equivalent T1 image contrast at different field strengths. For any tissue, T1 is always longer than T2. Although the relaxation processes characterized by T1 and T2 are physically different, both tend to increase with most disease processes, primarily due to the accumulation of fluid associated with oedema, inflammation and infection. Despite an overall increase in T1 with pathology, T1-weighted images are often favoured for the depiction of anatomical structure. Standard T1-weighted spin-echo images can be acquired in less time than their corresponding T2-weighted counterparts, due to the reduction in TR used to introduce the degree of T1 weighting. Images with T1 weighting are heavily influenced by the presence of the most common exogenous contrast agent, chelated gadolinium (Gd) (see section below on ‘exogenous contrast media’), which can cause a dramatic increase in signal on T1-weighted imaging (Fig. 5.8).

T2 (transverse relaxation time or spin–spin relaxation time) This time constant characterizes the rate of phase dispersion of the spins’ magnetization in the transverse plane (perpendicular to the main field). This fanning out of the x–y magnetization occurs as the protons exchange energy (or quantum, mechanical chatter) with each other. For a given tissue, the dependence of T2 on B0 is small when compared to that of T1. Fluids have long T2 values (typically 600–1200 ms) those of soft tissues being shorter (typically 50–200 ms) and fat shorter still (10–100 ms). All of these are shorter than their corresponding T1 values: for a given tissue, absolute T2 can never exceed T1. The elevation of T2 in disease processes leads to a very high



MAGNETIC RESONANCE IMAGING: BASIC PRINCIPLES

sensitivity using a standard T2-weighted spin-echo imaging technique, which is often the ‘bread and butter’ sequence for detecting lesions. When exogenous contrast media are administered, T2 is shortened. This mechanism is commonly used in abdominal imaging. For the use of Gd-chelates in the central nervous system (CNS), this effect is generally less and rarely used by comparison to its corresponding T1 effect. However, monitoring the passage of rare earth metals such as Gd is routinely performed using its modulatory effect on a closely related parameter, T2*.

T2* and endogenous susceptibility The concept of T2* was introduced above. When an image is weighted by T2*, not only is it weighted by tissue T2, but also by another component that can be ascribed to the hastening of the intrinsic spin–spin interaction by perturbations in the local magnetic field. Such perturbations are caused by the presence or introduction of objects that have different magnetic susceptibilities (χ). Magnetic susceptibility defines how magnetized an object becomes when placed in a magnetic field. When adjacent structures inside the homogeneous MR magnet have different χ, a small magnetic field gradient will be present. This gradient is the perturbing agent. Most of the constituents of the body are diamagnetic, having weak susceptibility, and they lead to a subtle reduction in the field that passes through them. Exogenous contrast agents (e.g. Gd-chelates) and some endogenous agents (such as deoxyhaemoglobin) exhibit paramagnetic properties which enhance local magnetic flux. Ferromagnetic objects exhibit an extreme form of paramagnetism, experiencing strong forces when placed in a magnetic field. Increasing B0 leads to shortening in T2* and an increase in T2* contrast. Artefacts can result from local decreases in T2*. Signal dropout adjacent to nonferrous metallic implants can be dramatic, even on low- and mid-field strength systems

Figure 5.8 Typical appearance of a brain tumour, specifically a cerebellar medulloblastoma. (A) The tumour has a low signal on spinecho T1-weighted images owing to a prolonged T1. (B) After the injection of Gd-DTPA the tumour enhances avidly, depicting breakdown of the blood–brain barrier.

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(0.2–1T). At high field, signal dropout occurs at the edges of various intracranial structures, such as the base of the frontal lobes, due to differences between the χ of cortical parenchyma and air within the sinuses. Dropout can be minimized by the use of spatially localized high-order shimming and increasing sequence bandwidth (number of Hertz per pixel). The presence of endogenous susceptibility gradients can be put to good use, providing a valuable contrast mechanism. One such example is BOLD f MRI, used not just within clinical neuroradiology, but also within associated neuroscientific specialities such as psychiatry and psychology. It is able to detect regional haemodynamic responses to simple or complex stimulation tasks. Although still not totally understood, neuronal/synaptic activity results in a change in local energy consumption which gives rise to an alteration in the ratio of intravascular oxy- and deoxy-haemoglobin and blood flow: the result being a localized net increase in the amount of fresh oxyhaemoglobin and hence T2*-weighted signal.This contrast is very subtle: activity within the primary visual or motor areas leads to signal changes of the order of 2–3% at 1.5T which approximately doubles to 4–6% at 3T. Much data have to be collected, processed and compared using computer-intensive algorithms to obtain statistically significant contrast. Clinical applications include aiding pre-operative neurosurgical planning and intra-operative neurosurgical guidance (Fig. 5.9). There are numerous other important uses of endogenous susceptibility-related, T2*weighted contrast, such as the depiction and timing of blood breakdown products following haemorrhage (Fig. 5.10).

Exogenous contrast agents Several agents have been tested, approved and are commercially available. Two groups will be considered: Gd compounds (the most common) and super-paramagentic iron oxide particles (SPIOs). Being a rare earth metal, Gd is toxic in isolation. Its toxicity is negated by appropriate chelation: the initial product to be introduced uses diethylenetriamene penta-acetic acid for this purpose (Gd-DTPA, Magnevist, Schering AG). Predominantly administered by intravenous injection, Gd-DTPA is rapidly distributed

Figure 5.9 Blood oxygen level dependent functional MRI is being investigated for its use in aiding pre-operative neurosurgical planning and intra-operative neurosurgical guidance. These data were obtained from a patient with a glioma in the left parietal lobe. Areas of activation due to finger tapping are overlaid in orange/yellow. Two anatomical slices are shown for right-hand motion and left-hand motion. Activation that correlates with right-hand movement can be seen close to the top of the lesion (bottom right).

throughout the vasculature. It is excreted by the kidneys, having a biological half-life of approximately 90 min. The agent lowers localized T1,T2 and T2*, as outlined above. Decreased T1 leads to bright pixels on T1-weighted spin-echo images (the most commonly used contrast mechanism [see Fig 5.8]), and decreased T2 can lead to less intense pixels on heavily T2-weighted images, particularly at high Gd concentrations. The effect on T2* is dramatic: the decrease causes low signal on T2*-weighted images which, on a suitable dynamic dataset, depicts parenchymal perfusion in real-time (Fig. 5.11; see section on ‘perfusion’ below).

Figure 5.10 Haematoma. A patient presents with a history suggestive of subarachnoid haemorrhage but MRI shows an extensive left frontal haematoma. The haemoglobin in the haematoma is in different stages of breakdown as shown on (A) the spin-echo T1- and (B) fast spin-echo T2-weighted images. (C) Note the high signal rim on FLAIR imaging indicative of oedema. (D) Gradient-echo sequences are very sensitive for acute haemorrhage and show prominent ‘blooming’ of reduced signal due to susceptibility effects.

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Figure 5.11 Exogenous perfusion data obtained from a time series of T2*-weighted echo planar images in a 70-year-old woman who presented with amaurosis fugax and was found to have a 95% stenosis of the right internal carotid artery. (A) A base image shows two regions of interest within the middle cerebral artery territories. (B) A drop in signal intensity can be seen due to the first pass of the Gd-chelate from which (C) a concentration–time curve is calculated and a gamma-variate fit is performed (solid lines). (D) The resultant time-to-peak (TTP) map shows prolonged TTP in the affected hemisphere shown as high signal.

Gd-chelates do not cross the intact blood–brain barrier, but accumulate where it has been compromised (e.g. intracranial tumours, abscesses and acute demyelination).This has been one of their primary clinical uses. They are particularly effective in the delineation of small tumours, such as acoustic neuromas. High-grade malignancies generally show more enhancement than tumours of lower grade. Areas of cystic necrosis may also show enhancement but the greatest clinical value of chelated Gd has been in distinguishing tumour from oedema. Care should be exercised as the integrity of the blood–brain barrier may be altered by the modulatory influences of corticosteroids. Applications outside the CNS benefit, for example, dynamic contrast uptake characteristics may aid breast lesion differentiation. Having Gd-chelates ‘on-board’ can increase overall vessel conspicuity when using standard TOF or phase-contrast angiography techniques, although the most common angiographic application is in contrast-enhanced MRA (CE-MRA)



MAGNETIC RESONANCE IMAGING: BASIC PRINCIPLES

and MR digital subtraction angiography (MR-DSA), where blood T1-shortening effects are used to visualize the passage of a bolus of contrast medium. If a particularly ‘tight’ bolus is needed, higher concentrations are available (e.g. 1 M Gadovist, Schering AG). Oral preparations can be used to visualize the gastrointestinal tract. The other class of agents considered here, SPIOs, is primarily for use in liver (Fig. 5.12) or spleen imaging (Endorem, Guerbet; Resovist, Schering AG).These particles have also been used in oral form for labelling the gut. In clinical applications to date, relatively large particles have been used which, after intravenous injection, lodge in the reticulo-endothelial system (Kupfer cells). Once lodged, they cause strong perturbations to the main magnetic field, producing a loss of transverse coherence, shortening T2. Tumours or other lesions which do not have reticulo-endothelial cells do not take up the SPIO and retain their high MR signal on T2- or T2*-weighted imaging. Lesions down to a few millimetres in diameter can be delineated in the liver.These iron-based agents are metabolized into the iron pools of the body and are excreted over a period of weeks. A selection of other exogenous contrast agents is available or under development, including coated iron-oxide and Gdcomplex blood-pool agents/strong albumin binding agents, hepatocyte-specific Gd-chelates (MultiHance, Guerbet), manganese-containing agents (Teslascan, GE-Healthcare) for the liver, pancreas and cortex of the kidneys; Mn-DPDP may be useful for assessment of acute myocardial ischaemia. Natural compounds, such as blueberry juice, may act as negative contrast agent in upper abdominal MR investigations, such as MR cholangiopancreatography. Other targeted agents, which may be necrosis specific (bis-Gd-mesoporphyrin), provide lymphographic contrast, or are specific for inflammation detection. The exact role of these agents is currently unclear, but they could considerably alter the practice of radiology.

Figure 5.12 Liver contrast agents—super-paramagnetic iron oxide particles (SPIOs). (A) Pre and (B) post iron oxide single-shot fast spinecho images. Both areas of FNH take up the iron oxide. Notice the central scar which has high signal on T2 and low signal on T1. (Courtesy of Dr A Blakeborough, Royal Hallamshire Hospital, Sheffield, UK.)

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Chemical shift, spectroscopy and water/fat imaging The phenomenon of chemical shift (δ) has important consequences for imaging as well as MR spectroscopy (MRS). In addition to the provision of clinical information, an overview of MRS can aid the understanding of many aspects and underlying principles of MR. Analytical chemists have used bench-top spectrometers since the 1950s in their quest to identify, understand and model molecular structure. The technique relies on information provided by chemical shift. In proton MRS (H-MRS), a hydrogen nucleus attached to a particular molecule does not ‘see’ the exact field produced by the magnet. This is because it is not a free proton; rather it is a proton in a chemical bond attached to a molecule. Neighbouring atoms that form that molecule have associated electron clouds which shield the hydrogen nucleus from the main magnetic field. The shielding effects within different molecules will differ. Back to the Larmor equation, since the resonant frequency is proportional to the field, the hydrogen nucleus will resonate at a particular frequency that is characteristic of that molecular environment. A measurement of the frequency components that emanate from a sample (in the absence of a frequencyencoding imaging gradient) will yield a frequency spectrum. This usually contains a number of peaks, the position of which (or shift along the frequency axis) is given in units of parts per million (ppm) of B0. Each peak can be attributed to a chemical group. Thus, MRS provides direct biochemical information. This can be spatially localized using a number of methods: by the spatial sensitivity of a surface coil, by the intersection of three slice-select gradients (single-voxel selection [SVS]), or a 2D or 3D metabolite map can be created by phase encoding the spectroscopic signal (chemical shift imaging [CSI]). It has become feasible to assess clinically important chemi-

cals and metabolities which are present in tissues in fairly low concentrations (millimoles in proton spectroscopy of the CNS). Spectroscopy is demanding in terms of the signal-to-noise ratio of the system and B0 homogeneity. The homogeneity within the spectroscopic region of interest must be such that any changes in resonant frequency are dominated by the chemical shift and not any heterogeneity in the applied magnetic field itself. Spectroscopy packages (particularly proton) have developed over the last 25 years to a stage where complex high-order shimming (B0 homogeneity optimization), signal localization, and data sampling and post-processing can be performed by ‘one-press’ button automation. Since its implementation in whole-body medical imaging systems, MRS has sometimes struggled to find a true clinical role. In part, that may follow from being seen as a disparate, complicated technique compared to MRI. On the contrary, it is often simpler. The technique has become more robust, forming part of a clinical investigative brain examination in many centres. It is often sensitive to the presence of disease, but lacks specificity; its clinical use (as for many imaging techniques) relies on other contextual information. Just as with standard imaging, spectra can be metabolite concentration-, T1- or T2-weighted, or a mixture of the three, depending upon acquisition parameters such as TE and TR. The brain has been the most extensively studied organ to date by proton MRS (Figs 5.13 and 5.14). If left alone, the hydrogen nuclei from water will dominate the MR ‘visible’ cerebral metabolites. This large peak from water (at 4.77 ppm) needs to be suppressed, so that an appropriate dynamic range can be obtained for metabolite detection. The three main cerebral metabolites are attributed to choline-containing

Figure 5.13 Two examples of the applications of proton spectroscopy in neuroimaging. (A) The patient is a child with known mitochondrial abnormality who presents with seizures. MRI shows extensive areas of hypoxic damage and proton spectroscopy shows the doublet characteristic of lactate. Lactate is not normally seen. The other three major peaks (choline, creatine and N-acetyl aspartate [NAA]) are normal except for a mild reduction in the Na/Cr ratio. (B) In comparison, a child with a cerebellar tumour shows a massive increase of choline and complete loss of NAA relative to creatine. This is highly suggestive of tumour and characteristic of medulloblastoma, which was confirmed on histology.

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Figure 5.14 A ‘metabolite map’ or chemical shift image (CSI) where phase encoding is used in two dimensions to map the spectral metabolites. This example shows the distribution of N-acetyl aspartate in a patient with a periventricular space-occupying lesion. A colour overlay is used. (Courtesy of Dr P. Pattany, University of Miami, Florida, USA.)

compounds (Cho) centred at 3.2 ppm, the total creatine pool (creatine plus phosphocreatine) at 3.0 ppm, and N-acetyl (NA) groups at 2.0 ppm (such as N-acetylaspartate [NAA] and N-acetyl-aspartyl-glutamate [NAG]). The biochemical role of NA is not completely understood, but the peak serves as a putative marker of neuronal integrity/function, being predominantly confined within neuronal cell bodies and axons. In a variety of disorders the NA signal may be decreased when there is little or no change on MRI. These include diseases in



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which there is acute or chronic neuronal loss, such as some of the dementias, chronic head injury, temporal lobe epilepsy and infective encephalopathies. In the latter, in particular HIV-associated encephalopathy, spectroscopy has been shown to follow clinical neurological status more closely than imaging following the administration of antiretroviral medication. Proton MRS appears complementary to MRI, which is generally of most value in acute and subacute disease. At short TEs (where T2 and modulation effects are reduced) more detail on other biochemicals within the brain, such as glutamate, glutamine and myo-inositol can be obtained. Phase-encoded CSI yields metabolite images whose spatial resolution is sufficient to allow differentiation between normal tissues and pathology. Potential applications of proton MRS to other organ systems have been investigated. Most notably it has been investigated for the diagnosis and staging of prostate cancer where the level of citrate decreases, while the choline peak is high. This is the reverse of findings in the normal peripheral zone of the prostate, where citrate is high and choline low, and benign prostatic hypertrophy with intermediate citrate and choline levels. From an imaging point of view, the slightly different resonant frequencies of fat and water can lead to band artefacts at tissue boundaries (the component water and fat images are shifted with respect to each other).These can be minimized by increasing the range of resonance frequencies covered along the frequency-encode direction (acquisition bandwidth); as ever, there is a trade-off as more noise is sampled. Chemical shift can be used to provide images of just water or just fat, or their relative contributions can be altered. Fat- or water-only images can be produced by selective excitation, where the centre frequency of an rf excitation pulse (ChemSat) of narrow bandwidth is placed over either the water or fat peak (Fig. 5.15). Another method utilizes interference effects between fat and water signals. It is useful to consider the phase of the signal. Because of the difference in resonant frequency, their signals will alternatively be in and out of phase. The detected signals cancel out when they are 180 degrees out of phase and add together when they come

Figure 5.15 Saturation of orbital fat using a chemical shift selective pulse. (A) Axial fast spin-echo T2 images in a 2-year-old child showing proptosis of the right eye. (B) Axial images through the orbits show a mass intermingled with the orbital fat and conal musculation. (C) The anatomy is clarified using a post Gd-DTPA fat-saturation sequence.

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back into phase. The phenomenon is like the beating effect from two musical notes which are slightly out of tune. At 1.5T, the first water–fat cancellation point occurs at TE = 2.2 ms (Fig. 5.16). Such imaging can provide invaluable information in certain areas (e.g. adrenal imaging).

Flowing spins The given description of the spatial encoding process in the earlier section makes a bold assumption for the production of artefact-free images – that protons stay still while they are being excited and their position is encoded. This is often a tall order for the patient in a magnet with an itchy nose and, of course, impossible for humans to have totally still spins while they have a functioning circulatory system! The different MRI behaviour of fluids can be harnessed to yield information regarding fluid flow. There are various forms of in vivo flow or flow-like movement that that can be imaged to provide spin-movement related contrast.

Macrovascular flow (angiography) Flow within large vessels (arterial and venous) can lead to various appearances using standard imaging techniques: vessels can be void of signal (Fig. 5.17) or often they return hyperintense signal. An understanding of the principles underlying the appearance of flowing blood on MRI has led to the development of magnetic resonance angiography (MRA), where the protons in flowing blood produce a high signal against a background of little or no signal from stationary tissues. Such high contrast datasets can be manipulated and viewed, often using maximum intensity projection (MIP) algorithms, to reveal projected vascular anatomy. The common contrast mechanisms can be split into three groups: (A) TOF; (B) phase contrast; and (C) contrast enhanced. Time of flight effects utilize differences in magnetization when very short TR is used. Contrast is provided between stationary background spins in the imaging volume and inflowing, fresh

Figure 5.16 Colorectal metastasis in a fatty liver. (A) In-phase and (B) out-of-phase T1 gradient-echo axial images at same level. There is marked loss of signal from the liver parenchyma on the out-of-phase image indicating fatty infiltration. Notice the metastasis in the right lobe, and an artefact from aortic pulsation in the midline. (Courtesy of Dr A Blakeborough, Royal Hallamshire Hospital, Sheffield. UK.)

Figure 5.17 Flow effects. This patient presented with right-sided seizures. (A) Fast spin-echo T2-weighted images show a large area of signal void within the area of the left sensorimotor cortex, which was present on all other sequences. This is characteristic of a high-flow vascular malformation. (B,C) Time of flight angiograms before (B) and after Gd-DTPA (C) confirm the presence of a large pial arteriovenous malformation.

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blood.The stationary spins are repeatedly exposed to the excitation pulse and, due to the short TR, there is not enough time for their longitudinal magnetization to return to equilibrium: it becomes saturated and there is a lack of magnetization with which to form a signal. The inflowing blood, on the other hand, experiences its first excitation pulse and it returns a high signal. This phenomenon provides endogenous contrast. The imaging volume can be encoded as a set of 2D slices or a 3D dataset. High field strength systems (3T in particular) can provide excellent vascular depiction due to high signal-to-noise ratio and prolongation of both the T1 of blood and stationary background protons (Fig. 5.18). Gradient-echo sequences with high T1-weighting are often used as they can be acquired at very short TR, maximizing the TOF contrast. Phase contrast techniques utilize the basic phenomenon that phase changes are introduced to the transverse magnetization when spins are exposed to a magnetic field gradient.This is put to use in phase encoding where the phase difference in a single TR is used to encode the signal at one spatial frequency in the phase-encode direction. If, after a time delay, the phase-encode gradient were to be reversed, then the phase differences in the spins across the sample introduced by the initial gradient will be completely reversed or rewound. This is only true for stationary spins. If a spin has moved in the direction of the gradient between its initial application and its reversal, then the spin will either not have been rewound enough or it will have been rewound too much. It will have developed an overall phase change. Thus, phase-contrast encoding is performed by a pair of additional ‘bipolar gradients’, the magnitude, duration and time interval between which will determine the phase change experienced by a spin moving at a particular velocity. This information can be used to quantitate the velocity of the moving spins. In qualitative PC angiography, velocity encoding has to be applied in more than one direction. For a 3D implementation, separate flow encoding is applied in each direction. As with the TOF technique, PC is also an endogenous contrast mechanism.

Figure 5.18 3D Time of flight MR angiography projection of an intracranial, middle-cerebral artery berry aneurysm.



MAGNETIC RESONANCE IMAGING: BASIC PRINCIPLES

Contrast-enhanced depiction of flow uses fast T1-weighted acquisitions to capture signal from a bolus injection of exogenous Gd-based contrast media. The addition of Gd into the vasculature causes a decrease in the T1 of blood which will appear bright on T1-weighted images. In order to delineate the arterial phase, the acquisition is required to be performed within one cardiac cycle. In practice, the low spatial frequency components are collected during the arterial phase as these form the major components of the image. Care is necessary in recognizing flow effects, for it is relatively easy to diagnose a solid lesion when all that is being seen is an unusual flow effect within a fluid-filled space.

Microvascular flow (perfusion) One of the key indicators of normal tissue function is that of normal arterial flow and tissue perfusion. Perfusion-weighted MRI has also been developed and can be performed with the aid of endogenous or exogenous contrast agents.The latter are by far the most common implementation. Techniques using endogenous contrast media rely on the rf labelling of proximal arterial blood, which can then be detected as it reaches an image plane selected through the region of interest. The noninvasive nature of this measurement makes it ideal in certain situations, e.g. in the assessment of placental perfusion in utero or when several repeat studies are needed. However, the contrast-to-noise ratios are less than those that can be obtained following the administration of exogenous contrast media. Gd-chelates are suitable exogenous agents for use in MR perfusion studies (see Fig. 5.11). The presence of the Gd–ion complex shortens both T1 and T2*. If a time series of T2*weighted images is acquired with high temporal resolution (approximately 1 frame s−1), the presence of Gd can be detected as a drop in signal as blood transporting the agent arrives at the image plane. A concentration–time curve can be obtained from which parameters such as bolus arrival time (BAT), mean transit time (MTT), time-to-peak (TTP) and relative blood volume (rBV) can be derived, and the application of the central volume theorem can yield information regarding relative cerebral blood flow (rCBF). Early MR perfusion studies performed using clinical systems were limited by image acquisition times. Fast gradientecho techniques (such as FLASH) could be used but usually on a single-slice basis. The introduction of EPI into the clinical setting has revolutionized MR perfusion imaging: enabling subsecond, multislice datasets to be acquired. As with diffusion-weighted imaging (DWI), most of the experience of perfusion-weighted imaging is in the brain, and particularly in stroke and other vascular abnormalities. Ischaemic stroke is usually due to occlusion of the cervicocranial vessels. The resulting reduced blood flow will have effects on the parameters measured by perfusion-weighted MR. In the acute setting the most commonly encountered changes are: increased time-to-peak; increased mean transit time; reduced cerebral blood volume and flow. It is hoped that a combination of DWI and perfusion-weighted imaging will permit delineation of the ischaemic penumbra in stroke, defining potentially

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salvageable tissue. Another area of interest is myocardial perfusion—used to provide information regarding the viability of the myocardium.

Very slow flow (molecular diffusion) The diffusion of water molecules is very slow random movement which can be thought of as slow directional flow when its randomness is restricted by a surrounding barrier (e.g. an axonal tract in brain parenchyma). Just as with arterial and venous intravascular blood flow and CSF flow, molecular DWI contrast can be introduced into MRI. The technique utilizes the same principles as outlined in the phase-contrast MRA section above: depending on the alteration in the phase of protons attached to water molecules as they travel along a magnetic field gradient. If a bi-lobed diffusion-encoding gradient pulse scheme is applied along one physical direction between the initial rf excitation pulse and data collection, any protons which are displaced along the direction of diffusion encoding will accumulate a relative phase change.Those that are stationary will not. The bipolar diffusion gradients are most commonly added to a single-shot EPI sequence, which enables a snap shot of the molecular diffusion to be obtained in one direction. This can be repeated along the three mutually orthogonal directions within the image plane. The degree of diffusion weighting can be changed by altering what is referred to as the b-value. The amplitude and duration of the bipolar gradients determine this b-value and images that have strong diffusion weighting require the application of very strong field gradients. Due to the inclusion of the time-consuming bipolar gradient scheme, data collection occurs at a relatively long effective TE and thus the diffusion-weighted images are also T2 weighted. This can lead to ‘T2 shinethrough’: high pixel values in areas of increased T2 as well as in areas of abnormal diffusion, which can lead to confusion! It is common practice to acquire a set of images with the bipolar gradients turned off, yielding a set of images with identical T2 but no diffusion weighting. Post-processing can then be performed to eliminate

the T2-dependent image contrast, yielding maps of apparent diffusion coefficients (ADCs). DWI is being assessed in many types of brain disease. Its major contribution appears to be in the distinction between cytotoxic oedema (which produces restricted diffusion) and vasogenic oedema (which does not restrict diffusion of water). The pathology that primarily produces cytotoxic oedema is ischaemia/infarction and DWI appears to be a sensitive and reasonably specific means of detecting ischaemic stroke. DWI is often used in conjunction with dynamic, Gd-enhanced perfusion imaging in the investigation of acute ischaemic stroke (Fig. 5.19).

PULSE SEQUENCES The most commonly used groups of pulse sequences are outlined below. Two main groupings are given: sequences where the echo results from the application of (A) an rf pulse and (B) a gradient.

Variations on a spin echo Basic two-dimensional spin-echo sequence In this pulse sequence; the digitized signal echo is produced by flipping the spins over in the x–y plane by a 180-degree rf pulse. This is applied at a time TE/2 after an initial 90-degree excitation pulse, producing a spin echo at time TE. Multiple slices are encoded by staggering each slice-selecting excitation pulse within each TR period and the Larmor frequency of each slice. Each of these slices experiences the application of one phase-encode step. Slice timing within each TR can be sequential (adjacent slices excited one after another: 1,2,3,4, 5…) or interleaved (1,3,5….2,4,6…): the latter is performed to reduce the effects of any overlap between slice edges that can occur at low TR (cross-talk). Parameters that alter image contrast are TE and TR. This is a very versatile sequence that can be PD, T2 or T1 weighted. PD-weighted images result if

Figure 5.19 Imaging of ischaemic stroke by multisequence MR. (A) An axial fast spin-echo T2-weighted image from a patient with an acute onset of left hemiparesis which shows a large area of T2 prolongation in the confines of the middle cerebral artery. The image is somewhat degraded by movement artefact as is often the case when using standard sequences in acutely unwell patients. (B) The single-shot fast spin-echo (imaging time < 1 s for one slice), which gives the same information. (C) A diffusion-weighted image acquired in 15 s shows high signal and (D) the apparent diffusion coefficient map shows a low signal, indicating an acute stroke.

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(A) TE is short (≤ 20 ms), thereby not allowing any differences in signal to evolve between tissues that may have different T2s, at the same time as (B) TR is long (≈ 3000 ms), enabling the spins to return to equilibrium between each rf excitation pulse. Differences in signal will be due to differences in the number of spins: a high PD will be represented by a bright pixel while a low PD will be represented by a dark pixel. If the TR is kept long, then as TE is increased (80–100 ms), different tissues with different T2 values will return different signals, and the T2 weighting of the resultant images will increase. In this case, tissues with long T2 values (e.g. CSF) will still have high signal at long TE and be represented by a bright pixel and vice versa. If on the other hand TE is short (to minimize T2 influences as in the PD-weighted case) but TR is decreased (≈500 ms), the T1 weighting of the sequence increases. The latter occurs due to different amounts of saturation experienced by tissues that have different T1 values. A tissue with a short T1 (e.g. fat) with respect to the specified TR, will relax back to equilibrium before the next excitation pulse: maximum magnetization will be available and so a bright pixel will ensue. A tissue with a long T1 (e.g. CSF) will not have time to relax back to its equilibrium state before the next excitation: only a small component of its longitudinal magnetization will and so the signal returned will be low and hence the corresponding pixels will be dark. Thus, pixel intensity resulting from a T1weighted spin-echo sequence (a partial saturation sequence) is inversely related to T1. A dataset can be obtained from the spin-echo technique in the order of several minutes.



MAGNETIC RESONANCE IMAGING: BASIC PRINCIPLES

slices can produce motion artefact-free images, but care should be exercised as unwanted movement can occur between slices, altering the relative slice positions. Blurring can occur in the phase-encode direction. Every phase-encode step is acquired at a different TE, leading to a variation of T2-weighting across spatial frequency components. All resultant images appear heavily T2 weighted. Use of the single-shot FSE (SS-FSE) technique includes MR cholangiopancreatography, imaging of the diaphragm, bowel imaging and imaging of the fetus in utero (Fig. 5.20). It is also useful as a fast T2-weighted screening sequence in a moving patient!

Inversion recovery In this sequence type, the magnetization is ‘prepared’ before the initial 90-degree excitation pulse by the addition of an 180-degree ‘inversion’ pulse.The signal obtained will be influenced by the relative degree of recovery experienced by the spins along the z-axis.The inversion time (TI) is the time allotted for this recovery process to evolve between the 180-degree inversion and 90-degree excitation pulses. The inversion pulse introduces heavy T1 weighting into this sequence. Specific forms of the technique are fluid attenuated inversion recovery (FLAIR) where the TI is chosen so that the magnetization from fluids is nulled (≈ 2200 ms) in the detection (x–y) plane and TE is long (80–100 ms), introducing a lot of T2 as well as T1 weighting. The combination of fluid nulling with T2 weighting is particularly useful in assessing lesions with prolonged T2 adjacent to fluid structures (e.g. periventricular demyelination; see Fig. 5.7). In this same acquisition, T1 shortening brought

Multi-spin echo More than one echo can be recalled per 90-degree excitation using multiple 180-degree rf refocusing pulses which yield image datasets with different contrasts (as they are obtained at different TEs).The maximum number of slices per TR will reduce as the number of recalled echoes increases. The most common type used in clinical practice has been the dual spin-echo with short and long TE datasets (≈20 and 80 ms, respectively) at long TR, yielding PD- and T2-weighted datasets, respectively.

Fast-spin echo or turbo-spin echo or rapid acquisition with relaxation enhancement (RARE) As mentioned previously, the introduction of more than one phase-encode, refocusing pulse and frequency-encoded echo per excitation pulse (increasing the echo train length [ETL]), can speed imaging up by factors of between 2 and 32. During any one TR period, different spatial frequency components in the phase-encode direction will be acquired at different TEs, leading to a complex mixture of image contrasts. It is impossible to produce images that are as heavily PD weighted as can be achieved with the standard spin-echo technique above. Both T2- and T1-weighted images are commonly produced.

Single-shot fast-spin echo or half-Fourier acquired single-shot turbo-spin echo (HASTE) This is an extension of the FSE technique that enables all phase-encoding steps to be obtained following one initial excitation. One slice is acquired at a time, in approximately 1 s. Covering a volume prone to movement with multiple single

Figure 5.20 Imaging of the fetus in utero using single-shot fast spin-echo. Each set of 20 slices takes 20 s to acquire. This fetus has agenesis of the corpus callosum.

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about by the presence of exogenous Gd-based contrast agents will return high signal due to the sequence’s T1 weighting. In short-tau inversion recovery (STIR), T1 is kept short, and is typically used to null signal from fat. An example of its use in this context is in the delineation of breast lesions. There are several other methods of fat suppression; such sequences often demonstrate subtle lesions to best effect.

Spin-echo echo planar imaging In this variant of EPI, several or all lines of k-space are swept through at once during the evolution and decay of the main echo. The main echo is produced by an 180-degree rf pulse, i.e. it is a spin echo which is less influenced by field heterogeneities than the gradient-echo variety (below). This spin-echo EPI variant tends to be used for DWI as it is less prone to susceptibility-related artefacts than the gradient-echo EPI variant (see below).The sequence is actually a mix of gradient echoes, refocused by the EPI technique, that occur during the evolution of the spin echo that results from the refocusing rf pulse. Readers are referred elsewhere for further explanation and discussion of mixed gradient and spin echo (GRASE) sequences which have mixed spin-echo/gradient-echo contrast features.

Variations on a gradient echo/field echo Basic two-dimensional gradient-echo sequence This is as above for the 2D spin-echo sequences, except that the echo is produced by a gradient (rather than an rf pulse), causing the components of the spin magnetization to refocus in the x–y plane, producing an echo, without ‘flipping’ them over (i.e. without using an 180-degree pulse) (see Fig. 5.3). Unlike 2D spin-echo sequences, reduction in signal amplitude resulting from faster dephasing due to the presence of magnetic susceptibility differences/localized heterogeneity is not cancelled in this technique. Images can have mixed contrast consisting of PD, T1 and T2* weighting. When a different type of echo formation is present (the Hahn echo), gradient-echo sequences can also be T2 weighted. An understanding of the Hahn echo is needed to understand how different combinations of these four parameters can be made to dominate the image contrast. The TR used in a gradient-echo sequence is often shorter than the component tissue T2 values. In other words, the magnetization in the x–y plane will not have dephased completely before the next excitation pulse is applied (unlike the transverse magnetization in the spin-echo sequence which completely dephases, even when short TR is used to introduce saturation of the longitudinal component, i.e. to introduce T1 weighting). This net transverse coherence plus the addition of a further rf pulse produces the Hahn echo. So, two echoes can be present: the gradient echo and the Hahn echo. Each or both of these echoes can be used as follows. 1 Spoiled gradient-echo or spoiled gradient-recalled echo (SPGR) or RF spoiled Fourier acquired in the steady state (RF-FAST) or T1 fast field echo (T1 FFE). Any magnetization coherence in the x–y plane can be destroyed by the addition of a gradient pulse or rf ‘spoiler’, applied towards the end of the TR period. This sequence is

often termed a ‘spoiled gradient echo’. There is no Hahn echo, just the gradient echo. At short TE (< 8 ms) and short TR (≈ 50 ms), T1-weighting predominates (as with spin echo at short TR, due to differential saturation effects), but the weighting is not as heavy as the T1-weighted spin-echo variants. FLASH is a variant of the spoiled gradient echo. Instead of an initial 90-degree rf pulse, a low flip-angled pulse (α) is used. Very short repetition times can be used as saturation along the z-axis is minimized; enabling fast acquisition times and refresh rates for dynamic and angiographic studies. A relatively long TE (≈ 18 ms) increases the T2* weighting, with low α (≈ 25 degrees), decreasing the T1 weighting, allowing the T2* weighting to dominate. 2 Contrast-enhanced Fourier acquired in the steady state (CE-FAST) or PSIF (mirrored FISP) or T2 fast field echo (T2 FFE). T2-weighted images can be produced by imaging the steady-state coherence or Hahn echoes (that build up over a few repetitions) and not the gradient echo. The Hahn echoes are sampled towards the end of the TR period and the effective TE is approximately twice the TR. 3 Gradient recalled acquisition in the steady state (GRASS) or fast imaging with steady-state precession (FISP) or Fourier acquired in the steady state (FAST) or fast field echo (FFE). Residual phase coherence at the end of each TR is not destroyed and both the gradient and Hahn echoes contribute to the image. Complex, combined T1/T2 weighting results.

Three-dimensional gradient echo Secondary phase encoding is performed instead of slice selection. The penalty associated with this is an increase in acquisition time. However, as gradient-echo sequences can run with very short TR, this is manageable with typical standard 3D gradient-echo acquisition times in the order of 5–15 min. Acquisition times can be reduced substantially (with lower coverage and resolution), enabling breath-hold techniques (10–20 s). The spatial resolution in the second phase-encode direction is generally less than 2 mm (above this, 2D techniques tend to be used) and the signal-to-noise ratio at high resolution is superior to 2D techniques. Isotropic, submillimeter voxels facilitate true 3D visualization strategies.

Magnetization prepared rapid acquisition gradient echo (MP-RAGE) or turbo-FLASH or inversion recoveryprepped fast spoiled gradient-recalled echo As with the inversion recovery spin-echo sequence, an inversion pulse is applied before the excitation pulse, producing a T1-weighted sequence that is often used with rapid 3D encoding for high-resolution imaging of, for example, brain malformations. Coupled with its ability to depict exogenous contrast medium which has traversed the damaged blood–brain barrier, it is also useful for intra-operative neurosurgical guidance.

Gradient-echo echo planar imaging This is similar to spin-echo EPI but the main echo is produced by a gradient lobe. This sequence is heavily weighted to reflect differences in magnetic susceptibility. It is often used

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for BOLD fMRI studies and EPI-based exogenous perfusion assessment.

SAFETY CONSIDERATIONS Undergoing an MR investigation or working in a MR unit does not involve exposure to ionizing radiation and no clear long-term biological effects have been reported. However, the environment is quite unusual, presenting several potential risks to human safety that need to be fully addressed by those who work in it and for those who have occasion to visit it. Each unit should have a set of local rules based on advice outlined in documents from the relevant regulatory bodies (UK’s Medicines and Healthcare products Regulatory Agency (MHRA), European Union, etc.) and all MR unit staff should be familiar with these. Inner and outer ‘controlled areas’ that have restricted access should be detailed. Accountability to the hospital’s radiation safety committee is to be commended, ensuring that incidents are reported appropriately and that necessary safeguards/recommendations are acted upon. The invisible MR environment includes potential effects resulting from the following.

Magnet Ferromagnetic objects (mainly containing iron, nickel or cobalt), when near to a magnet, experience a force of attraction towards the magnet bore (magnetic isocentre). The force depends upon factors including magnetic field magnitude, proximity, object mass and composition.The danger associated with this hazard is real: fatalities have resulted. All patients, visitors, non-MR personnel and pieces of equipment should be screened appropriately before entry into the controlled area. Cardiac pacemakers contraindicate entry as do intracranial aneurysm clips of ferromagnetic/unknown composition. In very high fields (>> 1.5T) mild sensory activations (such as visual magnetophosphenes and balance alteration) have been reported. There is no evidence that these are harmful. If the magnet’s liquid helium/nitrogen Dewar is being replenished, the magnet room should be kept clear due to risk of cryogenic burns and suffocation. There may be occasion when the magnet needs to be shut down in an emergency, e.g. if a person becomes trapped between the magnet and a ferromagnetic object. Once the emergency run down unit (ERDU) button is depressed, liquid helium will vaporize and there is a valve/ pipe system to vent this gas to the outside. However, as a matter of caution, all personnel should exit the magnet room and the door should be kept closed.

Time-varying magnetic field gradients At high amplitudes and slew rates, these can cause unpleasant peripheral nerve stimulation. This is an acute effect and not harmful. Modern system software will alert the operator when there is risk of attaining such levels. The acoustic noise generated due to the fast switching of currents within the gradient coils while restrained in a high static magnetic field (an expensive loudspeaker!) may be considerable20, levels being up to



MAGNETIC RESONANCE IMAGING: BASIC PRINCIPLES

108 dBA. Protective ear plugs/headphones should be worn by patients (and accompanying personnel), particularly in systems operating at 1.5T and above. Recent advances in gradient coil design and construction have led to a decrease in gradientassociated noise on some systems for given performance levels.

Radiofrequency field The transmitted rf field deposits energy within the body. Energy deposition is expressed as the specific absorption rate (SAR) in watts per kilogram. The levels given in MHRA guidelines (for SARs applied over a 15-min period) have been set to limit tissue heating to less than 1°C. Modern system software indicates the SAR to the operator for each acquisition. Care should be exercised when examining anaesthetized patients who require ECG monitoring. Burns can result from rf Eddy currents being induced under the skin electrodes (e.g. where clinical indications suggest SAR-intensive sequences such as FSE imaging of the lumbar spine). In these circumstances, pain sensation cannot be communicated while a burn is developing. Caution should also be made when the patient’s circulatory system is compromised. Clinical need should be noted in cases such as these. MR is not advised during the first trimester of pregnancy. This is precautionary as no deleterious effects to mother or child are known. Patients with various implants (from deep brain stimulators to stents) should be assessed for possible interactions with static field and rf heating: evidence from an up-to-date reference should be sought. At the time of writing, an EU Directive covering work exposure to electromagnetic radiation is due to become part of UK law in 2008. It will affect working practices in clinical MR units. The relevant exposure is likely to be related to the time-varying fields produced by the gradient subsystem. Staff will not be able to stand at the entrance to the magnet bore to comfort the patient, initiate examinations from the magnet fascia, perform close monitoring of anaesthetized patients or take part in MR-guided interventional procedures. Various professional bodies are presently attempting to address these issues and it is hoped that these restrictions will not be necessary.

CONCLUSION In the first 25 years of clinical practice, MRI has moved from being a curiosity to being the technique of first choice in a variety of diseases. The physics necessary for image interpretation is more complex than that for any other technique in radiology, yet the great diversity of the technique provides a wide range of possibilities, many of which are being developed or are yet to be explored. Clinical MR is truly 3D, and with the advent of modern workstations there is an opportunity to obtain radiographic views that have not been available previously.The recent development of fast imaging ciné studies, perfusion and diffusion techniques, hyperpolarized gas imaging (Fig. 5.21) and solid

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Figure 5.21 Image of a healthy lung obtained with a two-dimensional, rapid, steady-state free precession sequence with 300 ml. Hyperpolarized 3 He at 30% polarization. (Courtesy of Dr J.M. Wild, University of Sheffield, UK.)

state methods provide new possibilities. The development of new contrast agents, targeted at specific organs, diseases, cell or gene types is likely to result in a considerable expansion of the options now available. Parallel acquisition methods promise radically to increase the throughput of MR techniques and allow contrast mechanisms, which previously could only be acquired statically, to be acquired in dynamic mode. Specialized MR systems targeted at specific body regions or diseases may increase access to MR and provide options for monitoring and even performing minimally invasive therapy. The full potential of MR is yet to be realized.

REFERENCES 1. Bloch F, Hansen W W, Packard M E 1946 Nuclear induction. Phys Rev 69: 127. 2. Purcell E M, Torrey H C, Pound C V 1946 Resonance absorption by nuclear magnetic movements in a solid. Phys Rev 64: 37–38. 3. Lauterbur P C 1973 Image formation by induced local interactions: examples employing NMR. Nature 242: 190–191. 4. Mansfield P, Grannell P K 1973 NMR ‘diffraction’ in solids? J Phys C 6: 422–426. 5. Mansfield P, Maudsley A A 1977 Medical imaging by NMR. Br J Radiol 50: 188–194. 6. Damadian R, Goldsmith M, Minkoff L 1977 NMR in cancer: Fonar image of the live human body. Physiol Chem Phys 8: 97–108. 7. Hinshaw W S, Bottomley P A, Holland G N 1977 Radiographic thin section of the human wrist by nuclear magnetic resonance. Nature 270: 722–723. 8. Hawkes R C, Holland G N, Moore W S, Worthington B S 1980 NMR tomography of the brain: a preliminary clinical assessment with demonstration of pathology. J Comput Assist Tomogr 4: 577–586. 9. Edelstein W A, Hutchinson J M S, Johnson G, Redpath T 1980 Spin warp NMR imaging and application to human whole body imaging. Phys Med Biol 25: 751–756. 10. Thomas D L, Lythgoe M F, Pell G S, Calamante F, Ordidge R J 2000 The measurement of diffusion and perfusion in biological systems using magnetic resonance imaging. Phys Med Biol 45: R97–138.

11. Wilkinson I D, Griffiths P D, Hoggard N, et al 2003 Short-term changes in cerebral micro-hemodynamics following carotid stenting assessed by MR perfusion imaging. Am J Neuroradiol 24:1501–1507. 12. Neumann-Haefelin T, Moseley M E, Albers G W 2000 New magnetic resonance imaging methods for cerebrovascular disease: emerging clinical applications. Ann Neurol 47: 559–570. 13. Taylor A M, Keegan J, Jhooti P, Gatehouse P D, Firmin D N, Pennell D J 2000 A comparison between segmented k-space FLASH and interleaved spiral MR coronary angiography sequences. J Magn Reson Imaging 11: 394–400. 14. Wilkinson I D 2005 Perfusion and diffusion imaging in chronic carotid disease. In: Gillard J, Waldman A, Barker P (eds) Clinical MR neuroimaging: diffusion, perfusion and spectroscopy. Cambridge: Cambridge University Press. 15. Paley M 1996 Human brain proton spectroscopy. In: Bydder G M, Bradley W (eds) Advanced MR imaging techniques. London: Martin Dunitz. 16. Schaefer S, Balaban R S (eds). 1992. Cardiovascular magnetic resonance spectroscopy. New York: Springer. 17. Ogawa S, Tank D W, Menon R, et al 1992 Intrinsic signal changes accompanying sensory stimulation: functional brain mapping with magnetic resonance imaging. Proc Natl Acad Sci USA 89: 5951–5955. 18. Rosen B R, Aronen H J, Kwong K K, Belliveau J W, Hamberg L M, Fordham J A 1993 Related articles advances in clinical neuroimaging: functional MR imaging techniques. RadioGraphics 13: 889–896. 19. Middleton H, Black R D, Saam B, et al 1995 MR imaging with hyperpolarized 3He gas. Magn Reson Med 33: 271–275. 20. Sodickson D K, Manning W J 1997 Simultaneous acquisition of spatial harmonics (SMASH): fast imaging with radiofrequency coil arrays. Magn Reson Med 38: 591–603. 21. Pruessmann K P, Weiger M, Scheidegger M B, Boesiger P 1999 SENSE: sensitivity encoding for fast MRI. Magn Reson Med 42: 952–962.

FURTHER READING Overviews Edelman R R, Hesselink R R 2005 Clinical magnetic resonance imaging. Philadelphia: WB Saunders. McRobbie D W, Moore E A, Graves M J, Prince M R 2003 MRI from picture to proton. Cambridge: Cambridge University Press. Reimer P, Parizel PM (rds) 2006 Clinical MR imaging: A practical approach. Berlin: Springer-Verlag.

Sequences design/spatial encoding/hardware Haacke E M, Brown R W, Thompson M R, Venkatesan R 1999 Magnetic resonance imaging: Physical principles and sequence design. Chichester: J Wiley & Sons. Holland G N, MacFall J R 1992 An overview of digital spectrometers for MR imaging. J Magn Reson Imaging 2: 241–246. Landini L, Positano V 2005 Advanced image processing in magnetic resonance imaging. CRC Press. Nassaivier M 1996 All you really need to know about MRI physics. Simply physics. www.simplyphysics.com. Robitaille P-M, Berliner L (eds) 2006 Ultra high field magnetic resonance imaging. Berlin: Springer-Verlag. Schmitt F, Stehling M K, Turner R 1998 Echo-planar imaging: theory, techniques and application. Berlin: Springer-Verlag. Schoenberg S O 2007 Parallel imaging in clinical MR applications. Berlin: Springer-Verlag. Tweig D B 1983 The k-trajectory formulation of the NMR imaging process with applications in analysis and synthesis of imaging methods. Med Phys 10: 610–623.

Diffusion, perfusion and spectroscopy Danielson E B, Ross B 1998 Magnetic resonance spectroscopy diagnosis of neurological diseases. New York: Marcel Dekker.

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Gillard J, Waldman A, Barker P (eds) 2005 Clinical MR neuroimaging: diffusion, perfusion and spectroscopy. Cambridge: Cambridge University Press. Warach S, Davis S 2003 Magnetic resonance imaging in stroke. Cambridge: Cambridge University Press. Young I R (ed) 2000 Methods in biomedical magnetic resonance imaging and spectroscopy. Chichester: J Wiley & Sons.

BOLD fMRI Buxton R B 2001 Introduction to functional magnetic resonance imaging: Principles and techniques. Cambridge: Cambridge University Press. Frackowiak R S J, Friston K J, Frith C D, Dolan R J, Mazziotta J C 1997 Human brain function. New York: Academic Press.

Exogenous contrast Jackson A 2005 Dynamic contrast-enhanced magnetic resonance imaging in oncology. Berlin: Springer-Verlag. Kauczor H-U (ed) 2000 Special issue: hyperpolarized gases in MRI. NMR Biomed 13: 173–264. Stark D D, Weissleder R, Elizando G, et al 1989 Superparamagnetic iron oxide: clinical application as a contrast agent for magnetic resonance imaging. Radiology 168: 297–301. Weinmann H-J, Brasch R C, Press W R, Wesbey G E 1984 Characteristics



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of gadolinium-DTPA complex: a potential NMR contrast agent. Am J Roentgenol 142: 619–624.

Angiography/cardiology/interventional Bogaert J, Dymarkowski S, Taylor A M (eds) 2005 Clinical cardiac MRI. Berlin: Springer-Verlag. Graves M J 1997 Magnetic resonance angiography. BJR 70: 6–28. Lee V 2006 Cardiovascular MRI: Physical principles to practical protocols. Philadelphia: Lippincott, Williams & Wilkins. Lufkin R B 1999 Interventional MRI. St Louis: Mosby. Morris E, Liberman L 2005 Breast MRI: Diagnosis and intervention. Berlin: Springer-Verlag.

Safety Medical Devices Agency 2002 Guidelines for magnetic equipment in clinical use with particular reference to safety. London: Medical Devices Agency. Moseley I F 1994 Safety of magnetic resonance imaging. Br Med J 308: 1181–1182. National Radiation Protection Board 1991 Principles for the protection of patients and volunteers during clinical MRI. NRPB 2 (no 1). Shellock S G 2006 Reference manual for magnetic resonance safety, implants, and devices: 2007 edition. BRPG. Shellock R, D Services Inc. www.mrisafety.com.

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6

James E. Jackson, David J. Allison and James Meaney

Multidetector CT angiography • Clinical applications Magnetic resonance angiography • Background • Contrast mechanisms • Post-processing • MRA in clinical practice • ‘Supplemental’ imaging: when is imaging of the lumen not enough? • Future directions Catheter arteriography • Technique • Preparation of the patient

• Contraindications • Anaesthesia • Arterial puncture • Digital subtraction angiography • Intravenous digital subtraction angiography (IVDSA) • Aftercare • Complications Catheter venography • Techniques • Complications Embolization techniques • Embolic materials and techniques • Indications for therapeutic arterial embolization

The imaging of blood vessels has changed considerably since the first edition of this textbook and, indeed, there have been significant new developments in cross-sectional imaging techniques even since the 4th edition. These have made many of the diagnostic catheter angiographic techniques described in previous editions almost obsolete. On the whole this is clearly a welcome advance; the newer multidetector CT angiographic techniques are obviously less invasive and, therefore, safer. Furthermore, in many instances these techniques will give more diagnostic information than could be obtained by conventional catheter arteriography because of the concurrent visualization of surrounding tissues and the ability to reconstruct the data in any plane. One of the disadvantages of the decline in the number of diagnostic catheter

angiograms performed, however, is that it has become more difficult for radiologists to acquire suitable expertise in the catheter techniques that are still required for more complex therapeutic interventional procedures. As a good understanding of the basic principles and techniques of catheter angiography remains essential for those intending to become interventional radiologists (and it becomes less likely that they will be able to obtain sufficient practical experience during their training for the reasons given earlier) it perhaps becomes more important that this information is available in this textbook. The newer cross-sectional techniques for imaging blood vessels will, however, be discussed first as these will, quite rightly, be requested before (and often instead of ) conventional catheter angiography.

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MULTIDETECTOR CT ANGIOGRAPHY (MDCTA) The development of CT machines combining a fan-shaped x-ray source and multiple detector rows has led to the ability to acquire image data from a large tissue volume in a single breath hold. With IV contrast medium and appropriate timing, exquisite images can be obtained of blood vessels during any particular vascular phase. Optimal imaging of the vessels requires the relatively rapid IV injection of iodinated contrast medium (usually 3–5 mls-1) and the acquisition of data at the appropriate time of vascular enhancement. The latter can be estimated based upon the ‘normal’ time of arrival of the contrast medium within the organ being imaged or, more commonly nowadays, by the more accurate use of contrast bolus detection technology. ‘Tight’ boluses of contrast medium using a chaser of normal saline may be useful not only to improve vascular opacification but also to reduce the total volume of contrast medium required. Depending upon the region and volume of the body being imaged hundreds, if not thousands, of axial images will be acquired; whilst all the diagnostic information is available in this data-set, evaluation of the axial images alone can be extremely time-consuming and is helped considerably by reconstruction of the data in axial, coronal, and oblique planes without loss of resolution, so-called multiplanar reconstruction (MPR). Tortuous vessels can be ‘straightened’ by curved MPR to aid in the assessment of luminal narrowing due to, for example, atheromatous disease or encasement by tumour. Maximum intensity projection (MIP) and volume rendering (VR) techniques are additional tools that help greatly in the assessment of blood vessels. Each of these reconstruction techniques has its advantages and disadvantages: 1 MPR is very useful for the rapid review of blood vessels in any plane including the surrounding bone and soft tissues, and will allow the assessment of vessel walls that might be obscured in MIP and VR techniques by the presence of, for example, calcification or an endoluminal stent. Each image, however, gives

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only one ‘slice’ of information and multiple separate images are required to see the vessel in its entirety (Fig. 6.1). 2 MIP techniques produce a planar image from a volume of data within which the pixel values are determined by the highest voxel value in a ray projected along the data set in a specified direction.The images obtained are those most similar to a conventional arteriogram but one of the clear disadvantages of this technique is that any tissue of high density (such as bone or vascular calcification) lying within the ray through a vessel will determine the pixel intensity instead of the contrast medium itself within the blood vessel (Fig. 6.2).This is a common cause of overestimation of vascular stenoses. 3 Volume-rendering techniques assess the entire volume of data with an attenuation threshold for display and produce a three-dimensional image. Typically, tissues are assigned a

Figure 6.2 An MIP image from an MDCT of a renal transplant artery clearly demonstrating the vascular anatomy.

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Figure 6.1 MDCT images of a gastroduodenal artery pseudoaneurysm. (A) An axial image demonstrates an enhancing pseudoaneurysm cavity surrounded by a large haematoma in the region of the pancreatic head. (B) A sagittal MPR image demonstrates a pseudoaneurysm arising from the gastroduodenal artery. (C) A further sagittal MPR image demonstrates that the right hepatic artery, from which the gastroduodenal artery arises, originates from the superior mesenteric artery.

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colour that is dependent upon their attenuation values, facilitating the differentiation of structures of differing density (Figs 6.3, 6.5). The final images can be rotated in real time to find the best projection to display anatomy and pathology and this is the most important feature of this technique. Vascular stenoses can be overestimated, however, and small vessels may not be clearly visualized. It should be remembered that, whilst these post-processing techniques are very helpful for diagnostic assessment and for display in multidisciplinary team meetings, the axial source images are essential and often allow the operator to distinguish between artefact and disease when an abnormality is suggested on reformatted views.

CLINICAL APPLICATIONS MDCT angiography (MDCTA) is replacing conventional angiography in many, if not all, body areas and is indicated, therefore, in any disease process that requires the visualization

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of blood vessels to improve diagnosis and outcome. Within the thorax, for example, this would include the assessment of: pulmonary embolic disease1,2 (Fig. 6.4); thoracic aortic disease3–5; coronary artery graft patency6–10; and bronchial artery anatomy and pathology in massive haemoptysis11. In the abdomen common indications include the pre-operative planning and posttreatment assessment of abdominal aortic aneurysmal disease12,13 (Fig. 6.5); the assessment of native and transplant renal arteries14–16; the staging of hepato-pancreaticobiliary neoplasms17–20; and the assessment of vascular complications in patients suffering severe trauma21. It is also used increasingly in the assessment of peripheral arterial disease in the lower (and upper) limbs where it is less invasive, less expensive and exposes the individual to less radiation than conventional catheter angiography22–26. The scanning technique (positioning of the patient, rate of contrast medium administration, time of image acquisition), and the post-processing techniques most suited to the different indications listed earlier will clearly vary and lie outside the scope of this chapter; interested readers are referred to other chapters within this book and to other texts cited in the reference list.

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Figure 6.3 The value of MDCT MPR and VR images in the assessment of pulmonary sequestration. (A) The CXR demonstrates a mass projected through the left side of the cardiac silhouette. (B) An axial image from an MDCT examination demonstrates a left paraspinal soft-tissue mass. A feeding vessel arising from the thoracic aorta is visible. (C) MPR and (D) VR images show the full length of the oblique course of feeding artery.

Figure 6.4 MDCT demonstration of bilateral pulmonary emboli. (A) Axial and (B) coronal MPR images demonstrating extensive bilateral pulmonary emboli in central pulmonary arteries.

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Figure 6.5 MDCT images of abdominal aortic aneurysmal disease before and after stent insertion. A large infrarenal abdominal aortic aneurysm is seen on axial (A and D), coronal MPR (B and E) and VR (C and F) images before and after the insertion of an endoluminal bifurcated stent

MAGNETIC RESONANCE ANGIOGRAPHY BACKGROUND Magnetic resonance angiography (MRA) is a method for generating images of blood vessels with magnetic resonance imaging (MRI)27,28. With improved understanding of the nature of the signals emanating from blood vessels on MR images, it became evident that rather than simply contribut-

ing a source of artefacts on MR images, flow phenomena could be harnessed to generate diagnostic ‘angiograms’27–29. MRA has undergone a revolution over the last decade, replacing catheter angiography as the primary diagnostic tool for the evaluation of most vascular territories (apart from the coronary arteries); this change is due mainly to the success of contrast-enhanced techniques30.

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CONTRAST MECHANISMS Unenhanced (time-of-flight [TOF] and phase contrast [PC]) MRA With these techniques, the intravascular signal depends on inherent properties of flow, and the MR parameters must be carefully tailored to ensure a high intravascular signal27,28. In the case of TOF MRA, for example, data must be acquired perpendicular (and ideally orthogonal) to the direction of flow, and the time between successive radio frequency (RF) pulses (the repetition time [TR]), must be sufficiently long to allow an adequate ‘inflow’ of fully relaxed protons into the imaging slice27.The TR, therefore, is dictated by expected flow rates within the regionof-interest and, typically, should be 35 ms or greater. As the data acquisition time is directly proportional to the TR (acquisition time = TR × number of phase-encoding steps × number of slices × number of excitations), a TR substantially greater than the shortest possible for gradient-echo imaging (3–5 ms) must be used, with resultant prolongation of scan time. Additionally, owing the predominant head–foot orientation of the major arteries (e.g. the aorta, ilio-femoral and infra-popliteal vessels), the axial plane must be used, which also prolongs the data acquisition owing to the large number of slices required. Despite ‘faster’ techniques, therefore, acquisition times for TOF MRA are artificially prolonged, firstly as a result of physiological bloodflow rates that mandate the use of a relatively long TR and secondly by the requirement for axial imaging, which affords poor spatial coverage in comparison with sagittal or coronal imaging30. Selective arteriograms or venograms can be acquired by employing a (travelling) saturation pulse placed downstream of the imaging slice for MRA (to eliminate venous return from the opposite direction) or upstream of the imaging slice to generate MRV’s (venograms). If no saturation pulses are employed, both arteries and veins are identified on the same image.

Time-of-flight MRA methodology and limitations TOF angiography relies on the fact that the blood enters the volume under consideration with relatively high velocity and traverses it quickly, so that it receives very few RF pulses27,28. In order to maintain a highest possible inflow effect, all protons within the imaging volume must be replenished between successive TRs, though maximal inflow may not be necessary in clinical practice and some trade-offs can be accepted.An oblique course of the blood vessel being imaged in relation to the slice orientation and short TRs both adversely affect signal-to-noise ratios (SNR) as a result of protons under these circumstances experiencing more RF pulses whilst in the imaging slice. The severity and length of stenoses also tend to be overestimated on TOF MRA images because of intra-voxel dephasing secondary to turbulent, slow or pulsatile flow. As a result of these limitations,TOF MRA has failed to offer a viable non-invasive screening alternative to conventional arteriography, and has not had a major impact on clinical practice.

Phase-contrast MRA Phase-contrast angiography (PCA) is now seldom used in clinical MRA. The methodology underpinning the technique

is somewhat complex and, like TOF MRA, images are prone to artefacts and data acquisition is lengthy29. The term ‘phase’ refers to the angle that the transverse magnetization makes relative to a reference axis. When protons are moving, for example, in flowing blood, a change in phase proportional to the distance the proton moves (and, therefore to blood velocity) is induced by the imaging gradients, in particular the slice-selection gradient and the frequencyencoding gradient. As these gradients actually consist of a pair of gradient pulses applied in opposite directions (so-called bipolar gradients), the effect of each gradient on the phase of protons for stationary (i.e. background, motionless) tissues is equal and opposite, and the effect cancels out. For moving (flowing blood) protons, the position of each proton will change between consecutive pulses resulting in a phase change relative to stationary protons that is proportional to velocity. This observation of gradient-induced phase change provides the basis for phase-contrast angiography in which the gradient pulses are designed to produce phase changes for a given velocity range. In this way, the signals do not cancel, phase information is preserved during the image reconstruction. Pixel brightness is directly proportional to the phase-shift acquired by a moving proton in the magnetic field and, therefore, to velocity. In practice, as the method is only sensitive for the velocity component applied along the flow-encoding gradient, the acquisition must be repeated a total of four times in order to generate an ‘angiogram’: an initial flow-compensated sequence is followed by three flow-encoded acquisitions one for each direction of flow (head–foot, left–right, anteroposterior), followed by a complex subtraction to generate the final angiographic image. As the phase is unchanged for static protons, the subtraction completely suppresses the signal from the background tissue thus facilitating the generation of high-quality images29. One of the major challenges of PCA relates to the requirement of the operator to appropriately select the velocity-encoding gradient.As the signal intensity is proportional to velocity, the range of velocities present within the vessels of interest must be inferred or measured to allow the operator to set the velocity-encoding gradient (Venc) correctly.This assumes an a priori knowledge of the blood flow velocities within the relevant artery and, though this can be rapidly measured directly by acquiring a series of 2D PC images with different phase-encoding values, it is time-consuming and the presence of different flow velocities within the arteries enclosed within a single field of view may introduce artefacts29.

Limitations of unenhanced MRA and requirement for contrast agents At each stage of the evolution of MRA, high accuracy was reported for almost all techniques when compared with catheter angiography27–29 but TOF and PC MRA did not gain widespread acceptance in clinical practice because of long examination times, suboptimal resolution and frequent artefacts. TOF MRA was used to evaluate disease involving the carotid bulb and the femoro-popliteal and pedal arteries as these vascular territories were ideally suited to this technique due to the relatively straight course of their vessels, which

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meant that adequate ‘inflow’ could be ensured. MRA was also established as an accurate modality for portrayal of the proximal intra-cranial arteries (despite the fact that the arteries demonstrate marked tortuosity) because of the relatively small volume of tissue that needed to be covered, coupled with the fact that constant blood flow within the cerebral arteries over the cardiac cycle optimizes intravascular signal29,30.

Contrast-enhanced MRA (CEMRA) Because of their unmatched high contrast-to-noise ratios, high spatial resolution, rapid speed of acquisition and relative freedom from artefacts, contrast-enhanced techniques have almost universally replaced non-contrast techniques in clinical practice30. Unlike TOF and PCA techniques, where the intravascular signal is dependent on inherent properties of flow and is, therefore, at the mercy of alterations in flow rate secondary to vascular disease, intravascular signal for contrast-enhanced MRA (CEMRA) depends on a T1 shortening effect induced by the injection of a paramagnetic contrast agent (usually gadolinium based). Images can, therefore, be acquired in any plane including coronal, which affords the best anatomical coverage for virtually all vascular territories outside the brain (Fig. 6.6). In addition, the ability to exploit ultrafast 3D acquisitions (by using the shortest TRs possible), allows rapid image acquisition that can easily be accommodated within a single breath-hold, an important factor when imaging in the chest and abdomen. In order to generate ‘selective’ arteriograms, images are acquired during the first arterial passage of the contrast agent before its arrival within the veins.The synchronization of data acquisition with the peak arterial bolus is one of the major challenges of CEMRA as the rate of transit of contrast medium from the peripheral vein injection site to the vessel of interest is affected by a number of factors including heart rate, stroke volume and the presence or

Figure 6.6 A surgically created dialysis (arteriovenous) fistula in the left arm of patient with chronic renal failure.

absence of proximal steno-occlusive lesions. Although the circulation time can be measured using a test bolus, or can be inferred by making some assumptions about the patient’s cardiovascular status, the process is now automated by employing an MR fluoroscopic approach – a technique that demonstrates contrast medium arrival in real time on the display monitor, thus signalling the appropriate time for data acquisition31. The unique nature of k-space (the array of data from which the final image is generated) whereby the central lines determine image contrast and the peripheral lines determine image resolution, can be uniquely exploited to generate CEMRA images with unrivalled signal-to-noise ratios32. In situations where breath-holding is not required (e.g. peripheral MRA and carotid artery imaging) as long as collection of the contrast-defining central lines of k-space is completed during the arterial peak before contrast medium reaches the veins, the continued collection of resolution-defining peripheral lines of k-space during venous enhancement does not result in venous contamination of the images32. CEMRA is now the standard of reference for MRA against which all new techniques must be measured.

POST-PROCESSING Regardless of which method is employed to generate MR angiograms, the aim of all techniques is to make the arteries the brightest structures on the images, and to extract the vascular data by means of a maximum intensity projection (MIP) computer algorithm28 (Figs 6.7, 6.8). Other methods of post-processing include multi-planar reformatting, volume rendering and surface-shaded displays. For phase-contrast MRA, there is inherent complete background suppression because of the absence of bulk motion in background tissues.

Figure 6.7 Normal MRA. Note clear depiction of the abdominal aorta, iliac arteries and renal arteries on the frontal MIP.

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monary angiography; and the fact that catheter pulmonary angiography, the reference standard against which new and improved MRA techniques should be compared, has largely disappeared from clinical practice due to the success of CTA, thus depriving MRA of a valid arbiter for comparative studies. Improvements in spatial resolution bring the subsegmental arteries within the realm of MRA (Fig. 6.9) and further refinements including MR perfusion and ventilation (mirroring the ventilation and perfusion components of nuclear medicine studies albeit at much higher resolution) offer additional functionality to determine the location and distribution of small emboli36.

Abdominal aorta, renal and mesenteric arteries

Figure 6.8 Severe left renal artery stenosis and right common iliac artery occlusion.

For TOF MRA, the background is suppressed by virtue of the short TR in relation to the longish T1s of background tissues. Although fat remains bright, it can be eliminated by use of fat-saturation techniques, albeit with an additional time penalty. For CEMRA, there is the additional benefit that the background tissues can be completely eliminated by the subtraction of a mask acquired before the injection of contrast material.

CEMRA is the MR technique of choice for imaging the aorta in its entirety and for evaluating its large and medium-sized branches including the renal (Fig. 6.8) and proximal mesenteric arteries30,37–40. Because of the need for breath-holding the technique’s spatial resolution remains inferior to that of catheter angiography because of the inability to collect a highresolution data-set that matches that of DSA during a breathhold. Nonetheless, numerous studies and meta-analyses attest to the accuracy of MRA in clinical practice38. An additional benefit of MRA lies in its ability directly to measure the flow rate to each kidney using a two-dimensional (2D) cardiactriggered, phase-contrast approach, which facilitates both the assessment of both end-organ damage and the likelihood of success of transluminal angioplasty37. MRA is also highly accurate for depicting the mesenteric arteries in patients with suspected chronic mesenteric ischaemia39. In patients with abdominal aortic aneurysms, the external dimensions of the aneurysm can easily be delineated, should this be necessary, with targeted pre-contrast or post-contrast

MRA IN CLINICAL PRACTICE MRA is an excellent technique for imaging most vascular territories but is generally avoided in unstable and/or ventilated patients and those with severe trauma because of the hazards of the MR environment and the difficulties in monitoring patients within the MR room. Standard contra-indications to MRI (pacemakers, intracranial uneurysm clips) also preclude use of MRA.

Thoracic aorta and great arteries Because of the relatively large size of these vessels, they can be demonstrated with a wide variety of techniques but CEMRA is favoured in most instances owing to its rapid speed of acquisition and the quality of the images generated33,34.

Pulmonary arteries Although several studies have established high accuracy for MRA compared with pulmonary angiography for the evaluation of suspected pulmonary embolism, it is not widely used clinically35,36. Reasons for this include a reluctance to refer potentially unstable patients to MRI; the availability of CT pul-

Figure 6.9

Normal pulmonary MRA.

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images as only the lumen is demonstrated with CEMRA40. Calcium within the wall is not demonstrated, however, and aneurysm assessment for planning endovascular stenting is usually performed with CTA.

Carotid arteries Because of the requirement accurately to differentiate stenosis at a 70 per cent cut-off within a relatively small (internal carotid) artery, there are stringent spatial resolution requirements for carotid MRA41. As the carotid bifurcation does not move with respiration a relatively long data acquisition that generates images with sufficiently high (isotropic) spatial resolution is recommended. Despite the fact that the resultant data acquisition is substantially longer than the arterio-venous transit

A

D

G

B

E

H

time of 8–12 s (the blood–brain barrier prevents the parenchymal extraction of gadolinium and therefore facilitates rapid transit from artery to vein), this does not lead to unacceptable venous contamination of the images as there is sufficient time within this arterio-venous window for acquisition of the contrast-defining central lines of k-space. Clearly, acquisition of these central lines must be synchronized with the peak arterial bolus by combining some form of bolus detection as described previously with a ‘centric’ order of k-space filling. In comparison with cathether angiography CEMRA has demonstrated high accuracy in evaluating the carotid artery, e.g. for differentiating between significant and insignificant stenoses, differentiating between critical stenoses and occlusions, and for depicting carotid and vertebral dissections (Fig. 6.10).

C

F Figure 6.10 T2, FLAIR and diffusion-weighted images in a patient with right-sided weakness and aphasia. All the images were acquired in the axial plane at the same level. (A–D) Note the high signal on T2 (A), FLAIR (B), and Diffusion-weighted images (C) (arrowed) with a corresponding low-signal intensity on ADC map (D), ringed indicating an acute cerebral infarct. (E, F) Whole-volume MIP images from a TOF MRA in coronal (E) and axial (F) orientation demonstrate reduced signal intensity within the left internal carotid (short arrows) and left middle cerebral arteries. Targeted MIP images of the left-sided carotid and vertebral arteries demonstrate a severe stenosis of the internal carotid artery just beyond the bulb (not shown). Axial T1 (G) and T2w (H) images with fat-saturation reveal crescentic high-signal intensity within the left ICA (long arrows) at the site of the stenosis demonstrated on CEMRA, diagnostic of acute dissection.

CHAPTER 6

• ANGIOGRAPHY: PRINCIPLES, TECHNIQUES (INCLUDING CTA AND MRA) AND COMPLICATIONS

Peripheral arteries In the peripheral arteries, as in most other areas, TOF MRA has been superseded by CEMRA. Although the spatial coverage offered by single-field-of-view imaging is insufficient to address all of the relevant anatomy, the introduction of moving-table MRA has opened the way for routine noninvasive MRA of the entire run-off arteries in a short timeframe ( 50

Eye/forehead

Nuclear medicine

2.04

5–10

injection and positioning of the patient on the couch, is difficult to shield. Typical doses received by staff in diagnostic imaging departments are shown in Tables 9.10 and 9.11.

Pregnant staff The dose to the fetus during the declared term of pregnancy (i.e. after the employer has been informed in writing) should be less than 1 mSv. For those receiving exposure to diagnostic X-rays this is equivalent to about 2 mSv to the surface of the abdomen. An individual risk assessment must be carried out for the pregnant employee but, as can be seen from Table 9.10, it is unlikely that a member of staff will exceed this dose.The evidence available indicates that there should be no need for a change in work patterns except perhaps for staff who are involved in a heavy interventional radiology workload or working with high activity unsealed sources (e.g. in the radiopharmacy). In these cases it may be advisable to change work schedules or to limit the number of procedures performed and to offer additional monitoring. However, it should be stressed that such measures are often mainly to give peace of mind to the staff concerned.

REFERENCES 1. ICRP 2000 Avoidance of radiation injuries from medical interventional procedures. ICRP Publication 85. Ann ICRP 30. Pergamon, Oxford. ICRP website: www.icrp.org/docs/ ICRP_85_Interventional_s.pps 2. ICRP 2001 Supporting Guidance 2. Radiation and your patient: a guide for medical practitioners. Ann ICRP 31. Pergamon, Oxford. ICRP website: www.icrp.org/docs/ ICRP_85_Interventional_s.pps 3. Dendy P P 2005 Low dose radiation risk: UKRC 2004 debate. Br J Radiol 78: 1–2 4. Watson S J, Jones A L, Oatway W B et al 2005 Ionising radiation exposure of the UK population: 2005 review. Health Protection Agency, Chilton 5. ICRP 1991 The 1990 recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Ann ICRP 21. Pergamon, Oxford 6. ICRP 2000 Pregnancy and medical radiation. ICRP Publication 84. Ann ICRP 30. Pergamon, Oxford. ICRP website: www.icrp.org/docs/ICRP_84_ Pregnancy_s.pps 7. ICRP 2003 Biological effects after prenatal irradiation (embryo and fetus). ICRP Publication 90. Ann ICRP 33. Pergamon, Oxford. 8. The Justification of Practices Involving Ionising Radiation Regulations 2004 Statutory Instrument 2004 No. 1769. The Stationery Office, London 9. The Ionising Radiation (Medical Exposure) Regulations 2000 Statutory Instrument 2000 No. 1059. The Stationery Office, London

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• RADIATION ISSUES: RADIATION PROTECTION AND PATIENT DOSES IN DIAGNOSTIC IMAGING

10. Royal College of Radiologists 2003 Making the best use of a department of clinical radiology: guidelines for doctors, 5th edn. Royal College of Radiologists, London 11. The Medicines (Administration of Radioactive Substances) Regulations 1978 SI 1006/1978. HMSO, London. And Amendment Regulations 1995 (SI 2147/1995) 12. Health and Safety Commission 2000 Work with ionising radiation. The Ionising Radiation Regulations 1999: approved code of practice and guidance. The Stationery Office, Norwich 13. Radioactive Substances Act 1993 (Chapter 12). HMSO, London 14. Hart D, Hillier M C, Wall B F 2002 Doses to patients from medical X-ray examinations in the UK: 2000 Review. NRPB W14. NRPB, Chilton 15. Institute of Physics and Engineering in Medicine 2004 Guidance on the establishment and use of diagnostic reference levels for medical X-ray examinations. Report 88. IPEM, York 16. Hart D, Jones D G, Wall B F 1994 Estimation of effective dose in diagnostic radiology from entrance surface dose and dose–area product measurements. NRPB-R262. NRPB, Chilton 17. Hart D, Jones D G, Wall B F 1996 Coefficients for estimating effective doses from paediatric X-ray examinations. NRPB-R279. NRPB, Chilton 18. Keat N 2002 ImPACT CT patient dosimetry calculator (version 0.99m). ImPACT, London. ImPACT website: www.impactscan.org/ctdosimetry.htm 19. Institute of Physics and Engineering in Medicine 2005 The commissioning and routine testing of mammographic X-ray systems. Report 89: 1987–1997. IPEM, York 20. ICRP 1998 Radiation doses to patients from radiopharmaceuticals. ICRP Publication 80. Ann ICRP 28. Pergamon, Oxford 21. Administration of Radioactive Substances Advisory Committee 1998 Notes for guidance on the clinical administration of radiopharmaceuticals and use of sealed radioactive sources. The Stationery Office, London 22. RADAR—The internal dose assessment system. RADAR website: www. doseinfo-radar.com/RADARIntSys.html 23. Institute of Physics and Engineering in Medicine 1998 Cost-effective methods of patient dose reduction in diagnostic radiology. Report 82. IPEM, York 24. Rawlings D 2005 Options for radiation protection of the patient. Br J Radiol 78: 877–879 25. Honey I D, MacKenzie A, Evens D S 2005 Investigation of optimum energies for chest imaging using film-screen and computed radiography. Br J Radiol 78: 422–427

26. ICRP 2004 Managing patient dose in digital radiology. ICRP Publication 93. Ann ICRP 34. Elsevier, Oxford. ICRP website: www.icrp.org/docs/ ICRP_93_digital_educational_version_20April04.pdf 27. Lewis M A, Edyvean S 2005 Patient dose reduction in CT. Br J Radiol 78: 880–883 28. ICRP 2000 Managing patient dose in computed tomography (CT). ICRP Publication 87. Ann ICRP 30. Pergamon, Oxford. ICRP website: www.icrp. org/docs/ICRP_87_CT_s.pps 29. Shrimpton P C, Hillier M C, Lewis M A et al 2005 Doses from computed tomography (CT) examinations in the UK: 2003 Review. NRPB-W67. NRPB, Chilton 30. National Radiation Protection Board 1998 Diagnostic medical exposures. Advice on exposure to ionizing radiation during pregnancy. NRPB, Chilton 31. ICRP 2002 Doses to the embryo and fetus from intakes of radionuclides by the mother. ICRP Publication 88. Ann ICRP 31, corrected version. Elsevier, Oxford 32. Winer-Muram H T, Boone J M, Brown H L et al 2002 Pulmonary embolism in pregnant patients: fetal radiation dose with helical CT. Radiology 224: 487–492 33. Cook J V, Shah K, Pablot S et al 1998 Guidelines on best practice in the X-ray imaging of children. St George’s Hospital, London 34. Paediatric Task Group of the European Association of Nuclear Medicine 1990 A radiopharmaceuticals schedule for imaging in paediatrics. Eur J Med 17: 127–129 35. ICRP 2004 Doses to infants from ingestion of radionuclides in mothers’ milk. ICRP Publication 95. Ann ICRP 34. Elsevier, Oxford 36. Becket J R, Kotre C J, Michaelson J S 2003 Analysis of benefit:risk ratio and mortality reduction for the UK breast screening programme. Br J Radiol 76: 309–320 37. Whitby M, Martin C J 2003 Radiation doses to the legs of radiologists performing interventional procedures: are they a cause for concern? Br J Radiol 76: 321–327

SUGGESTED FURTHER READING Institute of Physics and Engineering in Medicine 2002 Medical and dental guidance notes. A good practice guide on all aspects of ionising radiation protection in the clinical environment. IPEM, York

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Clinical Governance and Audit in Radiology

10

Richard A. Nakielny, Adrian Manhire and Raymond J. Godwin

Clinical governance in radiology • Definition of clinical governance • Setting standards for clinical audit • Risk management • Revalidation

Clinical audit—‘reality rather than belief’ • Clinical audit’s history and the wider perspective • The audit cycle/spiral • Achieving successful organization of audit • The re-launch of audit

CLINICAL GOVERNANCE IN RADIOLOGY Richard A. Nakielny In the mid/late 1990s a series of perceived major failures of the UK Medical Health System received intense media publicity. It was felt that the professional accountability of doctors to the public needed reinforcing.The government response culminated in two White Papers, The New NHS: Modern, Dependable1 and A First Class Service: Quality in the New NHS2, in which the concept of clinical governance was introduced and defined. These two White Papers signalled a culture change from an emphasis on numbers treated to an emphasis on quality of care, cooperation and patient involvement3. The new system is a multiprofessional approach which includes all the healthcare professionals within a clinical team. One of the objectives of this change was to reduce the substantial variations in medical practice and outcome across the country. It was recognized that this change would not happen overnight and the stated target was a 10-year programme of modernization of the NHS.

responsibility for the maintenance and development of service quality as well as the financial affairs of the Trust. Most NHS Trusts have set up committees in the following areas to satisfy external reviews of compliance with clinical governance: • Clinical audit (critical analysis of clinical care set against known standards) • Risk management • Clinical effectiveness (extent to which processes do what they are intended to do, i.e. greatest health gain from available resources) • Quality assurance • Staff development • Research and development.

DEFINITION OF CLINICAL GOVERNANCE

Local self-regulation, particularly through personal audit, is a cornerstone of clinical governance. All hospital doctors will be required to participate in a national audit programme appropriate to their specialty or subspecialty2. Within radiology, written standards related to equipment, process and appropriate clinical outcome need to be in place to comply with this aspect of clinical governance. Most radiology departments already have a substantial number of standards in place, particularly with regard to equipment and process. In addition, there are Royal College of

Clinical governance was defined as ‘a framework through which NHS organisations are accountable for continuously improving quality of their services and safeguarding high standards of care by creating an environment in which excellence in clinical care will flourish’. The essence of clinical governance is local accountability for the continuous monitoring and improvement of clinical quality.The Trust Chief Executive has statutory

SETTING STANDARDS FOR CLINICAL AUDIT

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Radiologists’ publications containing suggested standards4. These can be categorized under the following headings: 1 Equipment standards 2 Process standards: • Referral guidelines—there is national advice on referral guidelines5 • Requests for examination—legible, sufficient clinical detail, signed, dated, etc. • Procedure—target times for waiting lists, satisfactory patient identification, systems, informed consent, radiation, protection protocols, etc. • Patient care—written information about examination, acceptable environment, user satisfaction questionnaire, defined system for dealing with patient complaints, etc. • Reporting times • Critical incident reporting • Continuing professional development (CPD) for staff— induction programmes, fire regulations, radiation protection, cardiopulmonary resuscitation training, etc. • Staffing levels—national advice is available6. 3 Outcome standards These are much more difficult to set than process standards. There are few nationally accepted figures for minimum diagnostic accuracy in an everyday work situation.The accuracies of various imaging methods are published in the literature but these levels are often obtained by specialists who are working under optimal conditions. It is essential that any standards set under the auspices of clinical governance are practicable and achievable in the working situation. • Mammography screening—this was set up with process and outcome standards in position from the outset. However, mammography screening has the advantage of dealing with a single anatomical area and, in effect, a single pathological entity. This enables outcome standards to be more readily set and monitored than in the more complex everyday work situation where a wide number of investigations and pathologies are encountered. • Interventional radiology—The Society of Cardiovascular Interventional Radiology (SCVIR) in the USA has developed and published extensive standards relating to the success and complication rates of interventional procedures.The British Society of Interventional Radiology (BSIR) is developing a comparable set of practical and achievable standards. • Radiology—setting outcomes standards in other subspecialty areas of radiology is difficult and complex. National advice has been issued on possible audit projects7 but the majority are process rather than outcome audits. This illustrates the practical difficulties of identifying viable outcome audit projects. How, for example, does one assess the accuracy of a chest X-ray report other than on the most simplistic criteria? As the issue of standards in radiology is so problematical, it may be necessary to await central directives on standards in radiology from the National Institute for Health and Clinical Excellence (NICE) (NHS, UK) after appropriate consultation with national bodies and subsequently to set up audits

in these particular areas to ensure conformance with the standards set by NICE. In the interim it will be essential to develop an involvement with audit, not only to demonstrate departmental conformance with clinical governance, but also because individual revalidation by the General Medical Council (GMC) will require proof of audit activity.

RISK MANAGEMENT Clinical governance and risk management are inextricably linked. There are two main components of risk management: • the identification of potential problems which could compromise the safety of patients, visitors and staff • the installation of procedures and protocols to minimize these. There are already many areas of well-established risk management regulations including health and safety regulations, equipment maintenance and safety, radiation safety, infection control, cardiopulmonary resuscitation, IT security, etc. The introduction of clinical governance has raised the profile of several other important aspects in the practice of radiology.

Staffing levels/workload Clinical governance emphasizes quality of care, and adequate staffing levels are a prerequisite for this. Stress caused by understaffing will affect performance.There is at present a significant undersupply of radiologists in the UK to accommodate the increasing number of referrals and the complexity of modern radiology. The Royal College of Radiologists has attempted to define a reasonable workload for a radiologist, and also to assess the impact of new clinical appointments in other clinical specialties on radiology staffing6.

Skill mix Team-working is emphasized by clinical governance. There is national support from the Royal College of Radiologists for a responsible introduction of skill mix8 so that appropriately trained, supervised and audited (usually nonmedical graduate) staff can help to offset the radiological workload. An important prerequisite for this is that both the delegator and the person to whom the task has been delegated agree to the delegation which must conform to GMC guidelines9. In particular, it must be established that the person to whom the work is delegated is competent to carry out the task.This person then assumes a clinical and medico-legal responsibility for their actions but overall medical responsibility can only be transferred, by referral, to another medically qualified practitioner. It is essential that improved quality of patient care, rather than a reduction in costs, is the main aim of skill mix. Improved quality of care may be achieved with skill mix by releasing highly trained medical practitioners from time-consuming yet relatively straightforward tasks to allow them to concentrate on tasks that require a level of expertise commensurate with their ability and training.

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Continuing professional development The concept of lifelong learning is a firmly established component of clinical governance. It is not sufficient to view a qualification examination certificate, no matter how advanced, as being the final stage of medical education. Most radiologists have been voluntarily pursuing further learning throughout their careers and the formalization of this process does not pose any major conceptual difficulty. The public require reassurance that doctors, and indeed all staff, are keeping up to date with advances in medical knowledge. Documentation of this is a vital component of risk management and is also required for revalidation. Continuing medical education (CME) forms the backbone of continuing professional development (CPD) but CPD also includes the development of managerial, appraisal, teaching and other skills where appropriate.

Quality of reporting The quality and timeliness of reporting are central to the input into patient care by a radiology department. However, the setting of standards for quality of reports is problematical. In diagnosis, errors in perception are much more common than errors of interpretation. Overload of work, fatigue, repeated distractions and environmental conditions all have an important bearing on the incidence of these errors and it is important to minimize these adverse factors. Attendance at clinicoradiological and multidisciplinary team meetings is important to enable feedback on the accuracy of reporting to occur. Good communication between team members involved in clinical care is emphasized repeatedly in clinical governance. Formal records of attendance at these meetings would be useful documentary evidence for revalidation. Formal medical discrepancy meetings (see later) to discuss (anonymously) cases where possible errors have occurred are an essential development of clinical governance.

Working beyond competence All clinicians are becoming more specialized and radiology is no exception. Subspecialization is, however, a two-edged sword. It can produce a high-quality service during normal working hours but it also leads to a situation in which oncall work may be in an area outside the expertise of the consultant on-call. Consultant staff should together define who within the department has adequate expertise to perform and/or interpret the specialized procedures that may occur in an on-call setting. Arrangements should then be put in place, possibly involving other NHS Trusts, for on-call cover for these procedures. If such cover cannot be made available on an on-call basis owing to the local situation, risk managers must be made aware of this. National advice for on-call radiological practice10 includes the following: • Only those examinations that will affect immediate patient management during the out-of-hours period should be

• CLINICAL GOVERNANCE AND AUDIT IN RADIOLOGY

performed, and each department should have a portfolio of examinations that it believes can be offered safely and reliably out of hours. This list should be agreed with the Trust. • Out of hours, a radiologist should only carry out those procedures that they are competent to perform in normal working hours. • Appropriate staff and equipment must be available for outof-hours work that would normally be available for in-hours work. Another aspect of working beyond competence is the introduction of new radiological procedures. New procedures need to be evidence-based. Careful consideration should be given to organizing adequate study leave to acquire the skills for new procedures. The cost of complications incurred while performing a new procedure for which the radiologist is not adequately trained may be considerably more than the cost of obtaining training in that procedure.

Informed consent Clinical governance stresses greater patient involvement in decision making. The attitude of the general public to the amount and quality of the information they require before consenting to medical procedures has changed radically. The ease of access to information through the media and internet, together with an irreversible move away from the presumed infallibility of doctors, has resulted in a climate in which it is no longer acceptable to give inadequate information about medical procedures. In an excellent review of informed consent11, the differences in attitude in the UK and America were highlighted. In America the law requires that the patient is given all the relevant information. This contrasts with the UK where the law allows, to some extent, clinical judgement to determine what information is given to the patient. There must still be ‘sufficient disclosure’ to allow the patient to make an informed choice. The legal meaning of ‘sufficient disclosure’ is that patients must be informed of any serious risk, even if it is of low frequency. They must also be told of less serious risks which occur more commonly. Details/risks of a procedure may only be withheld if it is felt that they are likely to cause ‘serious harm to the mental or physical health of a patient’. If a patient asks a direct question about risks, this must be answered truthfully and as fully as the patient demands, i.e. information cannot be withheld if a direct question is asked. The GMC has issued advice on informed consent12. Aspects of this advice relevant to radiological practice in the UK have been incorporated into a guidance document issued by the Royal College of Radiologists13. Careful explanation and oral consent will be sufficient for the majority of radiological investigations. High-risk procedures require a full and careful explanation, and adequate time must be allowed for the patient to assimilate this information. This should occur prior to any pre-medication. Written aids and

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patient-focused literature have a positive role in this process. The person explaining the procedure must have sufficient knowledge and experience to answer any relevant questions fully and truthfully. Written consent is then required, but it is not a legal safeguard if complications arise that were not explained to the patient. If any information is withheld on the grounds that it may cause serious harm to the patient, this must be recorded before the procedure in the clinical notes together with the reason for doing so, as this may need to be justified in law. Examinations involving high radiation doses (e.g. CT, extended fluoroscopy) should have the risks/benefits of the procedure explained in terms that can be clearly understood. Again, pre-prepared information sheets may well be helpful. Research procedures must not be contrary to the interests of the patient, and a full explanation and written consent are mandatory.

Professional registration Policies must be in place for checking the professional registration of staff within the department. If the employment of certain groups of staff is subcontracted then the responsibility for confirming appropriate staff registration must be clearly defined.

Patient record security The confidentiality of patient records, both written and held on computer, is an important part of risk management. Clear policies must be in place for the maintenance of this security. Safeguards governing the access to, and storage of, confidential patient information must be in place.

Major accident response Clear policies defining the departmental response in the face of a major accident must be in place.

Critical incident reporting Clear policies for recording, openly discussing and disseminating any lessons learned from critical incidents must be in place. Any lessons learned must be applied promptly. The Royal College of Radiologists has produced an overview of the impact of risk management on clinical radiology14.

REVALIDATION Clinical governance incorporates both departmental and individual performance. The GMC have stated their view of the components of good medical practice for individual doctors9 and in future will require all UK doctors to undergo a revalidation process to maintain their licence to practise15. There is national guidance about how good medical practice impacts on radiologists16. However, the Shipman Inquiry findings17 (where a general practitioner was found guilty of the murder of more than 200 of his patients)

have criticized the proposed GMC revalidation procedure for failing to incorporate a robust assessment of a doctor’s fitness to practise. A leading article in the British Medical Journal18 succinctly discusses the rationale that underpins this criticism. The implementation of the GMC version of revalidation had been planned for April 2005, but this has now been postponed to allow for the incorporation of any future recommendations resulting from the Shipman Inquiry. The following is a summary of the principles of the GMC revalidation so far; however, it should be borne in mind that there will be additions to this when further recommendations are published, taking into account the findings of the Shipman Inquiry. • Individual clinical performance meets any national professional standards. • The basis will be appraisal and assessment of local performance in the workplace in relation to any appropriate national standards (i.e. an examination system is not thought to be appropriate). • It is seen to be fair to doctors and open and clear to the public and employers. • It is capable of appraising and assessing all doctors whatever the circumstances of their practice. • It is simple, unobtrusive, economical in time and effort, and is as inexpensive as is consistent with effectiveness (i.e. detailed performance assessment will only be invoked in cases in which there is local evidence of serious dysfunction in performance). It has been proposed that revalidation should be primarily based on the outcome of the local annual appraisal process for those employed within a managed setting, and will occur on a 5-yearly cycle. It will be essential for doctors to collect and maintain appropriate documentary evidence for revalidation. The GMC has stated that there will need to be evidence available in the following categories in order to obtain revalidation.

Suggested documentary evidence for radiologists 1 Good medical practice: • Audit results and record of attendance at audit meetings • Medical discrepancy personal records • Record of attendance at medical discrepancy meetings. 2 Maintaining good medical practice: • CME/CPD records • Personal development plan • Record of attendance at clinicoradiological and/or multidisciplinary team meetings. 3 Working with colleagues: • 360-degree appraisal documentation (see later) • Record of attendance at any radiology team meetings. 4 Relationships with patients: • 360-degree appraisal documentation (see later) • Record of complaints/plaudits.

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5 Research 6 Teaching/training: • Feedback documentation (anonymous). 7 Health/probity:

• Sickness record • Self-signed statement that ‘health (of the doctor) has never endangered patients or colleagues’ • Self-signed statement that ‘conduct work to highest ethical and moral standards’ • 360-degree appraisal documentation (see later). Most of the above documentary evidence can be collected relatively easily. However, documentary evidence for two of the cornerstones of clinical governance—namely medical discrepancy meetings (quality improvement by learning from errors) and 360-degree appraisals (team working)—requires more active organization. The following is a précis of suggested methods for setting up these two processes with the emphasis on simplicity.

Medical discrepancy meetings • Empathic lead person: involves everyone in the process, encouraging a constructive, nonconfrontational atmosphere. • Case collection: lockable collection boxes placed in easyto-reach sites with standardized forms adjacent (and replenished regularly!). • Meetings at regular intervals (e.g. monthly). • Cases presented by a lead person: the radiologist involved should remain anonymous. It is impossible to re-create the original reporting conditions but it is important to present the same clinical information that the reporting radiologist had available. • Discussion focused on learning, not blame. • Consensus vote on whether error actually has occurred. • Simple consensus scoring system for degree of error (grade and significance). • Lead person gives confidential feedback if an error has occurred. • Annual analysis by lead person of cases discussed to see if there are any patterns that may require a more structured solution. • Attendance recorded formally (documentary evidence for revalidation).

360-degree appraisal Satisfactory team working and a willingness to listen and act on constructive comments about performance from patients and colleagues (medical and nonmedical) are essential in clinical governance.Three hundred and sixty degree appraisal is a process where the views of patients and colleagues are

• CLINICAL GOVERNANCE AND AUDIT IN RADIOLOGY

gathered together and fed back to the individual at predetermined time intervals (approximately 3 years if there are no significant problems). Although 360-degree appraisal is viewed as an essential part of the overall appraisal process (and hence for revalidation), it must be stressed that 360degree appraisal is only one part of this overall appraisal, and is not a pass/fail process. The tasks and interactions of radiologists are different from those of physicians and surgeons. Consequently, the following suggested method for 360-degree appraisal has been adapted to conform to the requirements of radiologists, and has been issued as guidance by the Royal College of Radiologists on their website, www.rcr.ac.uk. The essence of the 360-degree appraisal questionnaire is as follows: • Five sections, the first three to be completed only by the relevant professional group (medical colleagues, radiographers/nurses and clerical/secretarial staff) and the final two sections to be completed by all staff groups. • Each section has about 10 simple questions relevant to that professional group in appraising the radiologist. There is a simple numerical scoring system ranging from 1 (poor) to 10 (excellent). • Within the radiographer/nurse section there are questions relating to patient interactions. This element allows radiologists with infrequent patient contact to obtain some documentary evidence for the ‘relationships with patients’ section for revalidation. • The penultimate section contains a simple question on the health and probity of the radiologist undergoing the 360degree appraisal. • The final section is for free text comments. • A pilot study has shown that the average time taken to complete the questionnaire is 7 min. • A minimum of 10–12 questionnaires (e.g. four from each of the three professional groups chosen) must be completed to give a reasonable overview and also to maintain anonymity of the staff completing the questionnaires. • A system for collecting the questionnaires anonymously and analysing them for feedback at the overall appraisal process needs to be in place. • A reasonable time interval between 360-degree appraisals, assuming there are no particular problems, would be 3 years to allow documentary evidence to be available for the 5yearly revalidation process. In an age where form filling is in danger of proliferating out of control, it is important that the 360-degree appraisal questionnaire is kept as simple as possible. If any significant problem areas are identified, these can then have in-depth assessment at the annual appraisal.

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CLINICAL AUDIT—‘REALITY RATHER THAN BELIEF’ Adrian Manhire and Raymond J. Godwin You will almost certainly have been referring to other chapters in this publication, using it as a reliable source of current opinion in diagnostic radiology, searching for best practice and the latest knowledge, and for research evidence in support of it. Having gathered such knowledge, are you able to show that you are practising to these new standards of care? Clinical audit is the tool that should enable you to produce evidence to show that you have achieved these standards in your own practice and you need to be able to do this. Audit is an integral part of clinical governance. In the foreword to Principles for Best Practice in Clinical Audit, Hine (Chair of Commission for Health Improvement) and Rawlins (Chairman, National Institute for Clinical Excellence) state19: Public and professional belief in the essential quality of clinical care has been hit hard in recent years, not least by a number of highly public failures. Clinical governance is the organizational approach for quality that integrates the perspectives of staff, patients and their carers and those charged with managing our health service. Clinical audit is at the heart of clinical governance.

One of the most prominent of the public failures was investigated in the Shipman report20. How well doctors carry out their professional activities has also been brought to the centre of public debate, along with the process of audit as a method of enquiry21. In this section, we review the origins of clinical audit, consider what audit is, how it can be carried out, how it can help underpin clinical governance, and how it might be built into departmental practices, creating the environment in which clinical audit can flourish.

The definition of audit The systematic, critical analysis of the quality of medical or clinical care, including the procedures used for diagnosis and treatment, the use of resources, and the resulting outcome and quality of life for the patient. Secretaries of State for Health, Wales, Northern Ireland and Scotland (1989)22

CLINICAL AUDIT’S HISTORY AND THE WIDER PERSPECTIVE Audit of medical care is not new. As early as the Crimean War (1854–1856), Florence Nightingale used a form of audit as an aid to her management of the injured and sick in her care, using standardized methods for the collection of information on death and infection23. She used this audit evidence to assist her argument for resources and changes in practice. In the United States, in 1917, the American College of Surgeons introduced a process of reviewing clinical notes against a set of minimum explicit standards, questioning their quality and adequacy of facilities (including radiology)24. These processes developed into criterion-based patient outcome audit

by 1975 under the overview of a national body, the Joint Commission on Accreditation of Healthcare Organisations25. At the same time, mainly as an aid to keeping public healthcare spending under control, the US Congress created Professional Standards Review Organisations. These were instituted to review the appropriateness of medical services and their quality through medical audit. There is a marked similarity to the development of the Commission for Health Improvement (CHI) and the UK National Institute for Health and Clinical Excellence (NICE).

Audit in the UK In the United Kingdom, prior to the late 1980s, there was no requirement within the NHS for clinicians to demonstrate any evidence of the quality of their clinical practice. In 1989, the UK government introduced medical audit as a requirement within all doctors’ job plans22, extended this in 1997 to include all healthcare professionals as clinical audit1,2,26, and integrated it into clinical governance. Together with the logical requirement to practise evidence-based medicine, the infrastructure for clinical governance was now in place, awaiting its formal introduction2. Not only is there now a mandatory requirement for all doctors to participate in clinical audit, the GMC9 advises all doctors that they: …must take part in regular and systematic medical and clinical audit, recording data honestly. Where necessary, you must respond to the results to improve your practice, for example by undertaking further training.

Although most doctors routinely practise audit informally by comparing their work to published data, there is now a clear obligation to record this and have it available to validate their personal practice and that of their clinical team, department and hospital.

Making it possible There are two factors that are important for successful audit: • creating a local environment that is supportive of audit (including providing adequate resources in terms of time and assistance, and ensuring that the resulting change occurs) • using audit methods that are most likely to lead to audit projects that result in real improvement.

Difficulties in audit Many of those involved in audit have unfortunately lost enthusiasm because of the difficulties that they have encountered. • Poor project design has led to data of poor quality. Information has been collected because it is available rather than being a relevant measure of clinical quality. • Many projects are poorly managed. Demonstrating inadequate care is not sufficient unless it can be carried through into changes that improve practice. Change is

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often the most difficult part of audit but it is often left to inexperienced junior staff without appropriate support, influence and resources. As much attention needs to be devoted to change for improvement as to the collection and analysis of data. It is the perception of improvements in care that drives the individual on to further audit.

What does audit really mean? Many clinicians find the term ‘audit’, with its financial undertones and rather formal definition (above), confusing and difficult to remember. Fowkes27 has given a more pragmatic definition: ‘Comparison of actual practice to a standard of practice and as a result of the comparison, any deficiencies in actual practice may be identified and change undertaken to rectify the deficiencies.’

The words ‘actual practice’, ‘standard of practice’, ‘comparison’, ‘deficiencies’ and ‘change undertaken to rectify’ clearly describe the audit cycle and emphasize the essential need for change for the better if standards are not achieved. Donabedian28 has subdivided audit into three types: structure, process and patient health outcome. Structure—What you need The availability and organization of resources (material as well as human) required for the delivery of a service. An example of this is the availability of adequate resuscitation equipment within a department of radiology. Process—What you do How well has a required procedure been followed? Have all radiology reports been checked and validated by the reporting radiologist prior to circulation? Patient health outcome—What you expect This describes the alteration in healthcare status of an individual which is directly attributable to clinical intervention. Outcome audits in radiology are often related to interventional radiology procedures, where the clinical improvement achievable with such techniques is more readily measured; however, it is not unreasonable to include accuracy of imaging diagnosis as an outcome audit, as it can also aid in the patient’s clinical improvement or cure29.

Audit is not research Research and audit are often confused.There are clear differences, the awareness of which enables differentiation. Donabedian30 distinguished between the assessment of medical technology Table 10.1

• CLINICAL GOVERNANCE AND AUDIT IN RADIOLOGY

(research) and the assessment of the quality of medical care (audit) (Table 10.1). The most important illustration of these differences is that an audit can be carried out on a relatively small number of cases and does not always require the time and expense of a research programme. Research sets the standards and audit determines whether clinical practice meets them.

What not to audit There is a tendency for new users of audit methodology to use it as a tool to demonstrate the inadequacies of other clinicians’ practice. It is tempting to audit how others use imaging services and the use of the published guidance on how best to use imaging encourages this31,32. Audit of third parties is unlikely to achieve the essential elements of change and improvement, which are the key features of a successful audit33. All involved should be committed to the audit or it will generate ill-feeling and the results are likely to be dismissed or ignored. Using such standards as part of an inclusive multidisciplinary audit process alongside nonradiological colleagues is much more likely to achieve change and reinforce, not strain, local professional relationships. Audit of personal practice should take the prime place. A standard is the keystone to the process and unless a clear standard is identified at the beginning of an audit, it is unlikely to succeed. It helps to ensure that a project is audit and not research. Audit activity must be relevant to current local activity and needs, and must reflect the problems encountered in everyday work.The likely required change should be achievable, otherwise effort used in trying to implement it is likely to be wasted. It is also better not to attempt audits with a high level of complexity, as these are more likely to fail to complete their second cycle34.

THE AUDIT CYCLE/SPIRAL The main aims of audit are to demonstrate either: • compliance with an agreed standard of care, or • to use the results of the initial audit to identify possible change(s) which, following implementation of those changes, may enable the standard to be achieved. The original concept was the audit cycle (or loop) (Fig. 10.1). Firstly, a topic is chosen for audit and a standard is identified. By identifying a suitable indicator (see later) and collection of related data, the reality of practice is identified and compared with a previously agreed target. • If the set target is achieved, the audit, on this occasion, is completed, reassurance has been achieved, and the audit result is available as governance evidence.

DIFFERENCES BETWEEN RESEARCH AND AUDIT

Research

Audit

Identifies what is best practice

Determines if this has been put into practice

Is concerned with techniques, instruments or materials

Is concerned with the performance of individuals or teams

Uses statistical models and usually requires statistical compliance

Does not have to reach statistical significance

Usually requires a long time scale for completion

May be carried out in a very short time (sometimes a matter of a few hours)

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Select a topic

Accept a standard of practice (e.g. from Research)

Observe your practice (i.e. Audit)

Implement change

Compare your practice with the standard

Figure 10.1 The audit cycle.

• If the target is not achieved, the need for some form of change is indicated to enable the required improvement in performance. After the introduction of the agreed change(s), the process of data collection is repeated. The second cycle will show if the changes have improved practice and whether the target has been achieved. The concept of the audit spiral (Fig. 10.2) adds a third dimension of continued improvement, recognizing that standards and targets can change with time and new developments. The more important audits are likely to be continuous processes, with multiple cycles year on year, rather than closed loops.

a successful audit such as the success and complication rates of angioplasty. Audit is a tool for showing how a practitioner measures up to local and national standards which are now becoming more readily available. In the UK, nationwide audits are now organized by the Royal College of Radiologists (RCR) or one of the affiliated clinical interest bodies, such as the audit of nephrostomy practice (RCR and British Society of Interventional Radiology).This enables comparison of local practice and its outcomes with similar institutions across the country. At the individual level, the collected evidence may assist in revalidation, and take its place in a personal folder for discussion at annual appraisal. However, with clinical governance, there is a need to demonstrate corporate accountability for clinical performance2 through a process of ‘regular and systematic formal Clinical Review’ (or clinical audit). Quality monitoring within the specific areas described earlier will be essential to provide this evidence. Some of these areas may require the creation of running audits as a monitoring process (e.g. waiting times for radiological examinations). Suggestions for what these areas of audit could be are available in a publication from the RCR35 which contains illustrative recipes. Topics and standards for governance issues are frequently incorporated into NICE guidance and Department of Health publications. An illustration of likely audit activity related to governance is shown in Figure 10.3. It is also possible to prioritize the choice of subjects for audit using the list below36, recognizing that not all areas can be audited at once. As an aid to prioritization, consider audit topics of activities which involve: • high risk • high volume • high cost • wide variation in clinical practice • local clinical anxiety (e.g. untoward events or questionable clinical performance).

Choosing topics to audit

What standard should be used?

Areas of concern in clinical practice that arouse the interest of an individual are more likely to produce enthusiasm for

When designing an audit, it is essential to identify an appropriate standard at the beginning of the process.

Figure 10.2 The audit spiral. (From Godwin R J, DeLacey G, Manhire A (eds) 1996 Clinical audit in radiology: 100+ recipes. Royal College of Radiologists, London, with permission.)

5 Re-audit 1 Select a standard 4 Implement change 2 Assess local practice

3 Compare with standard

Improvement or reassurance

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• CLINICAL GOVERNANCE AND AUDIT IN RADIOLOGY

Adverse events detected. Investigated. Lessons learnt and translated into change in practice.

Poor clinical performance identified early. Then dealt with skilfully, speedily and sensitively, in order to avoid harm to patients.

Quality of data necessary for monitoring clinical care to be of a consistently high standard.

Leadership skills developed at the clinical team level.

Systematic learning from clinical complaints. Translated into change in practice.

Where is your evidence

?

Continuing professional development programmes in place.

Quality improvement processes (clinical audit) to be integrated into an organizational quality programme.

Clinical risk reduction programme in place and of high quality.

Evidence-based practice and infrastructure in place and utilized.

Clinical audit will provide: • the evidence • indication of where changes need to be made • the help needed in order to meet the Trust’s statutory obligation1,2

Figure 10.3 Acquiring the evidence on effective governance. (Courtesy of Dr G DeLacey.)

Standards may be based upon research evidence, but this is frequently not available. A guideline may also be used as a standard, derived either nationally (e.g. from a specialty group or the National Institute for Health and Clinical Excellence) or locally agreed, based upon the best available information, respected opinion and local circumstances. Each standard has three components: A recommendation + an indicator + a target A Recommendation: a statement about the structure, process or outcome against which the quality of performance is to be judged. B Indicator: the variable (or item of information) that needs to be measured in order to determine whether the recommendation is being met.This is also known as the criterion. It may be represented as a percentage of compliance with a standard. C Target: the expected level of achievement or the minimum score that is considered locally to be acceptable in

good practice. It may be that when auditing for the second or third time, the target can be gradually raised. In this way, early failure, disappointment and disillusion might be avoided33.

The measurable indicator There may be more than one indicator within a single audit, each representing a step along a multilevel standard. This situation arises within audits of care pathways, where a number of criteria for completeness are required for the standard to be achieved. As an example of an indicator within an audit of double reading of breast screening mammograms, the recommendation might be that ‘all screening mammograms will be read by two radiologists’. The indicator here would be the actual percentage of mammograms reported by two radiologists.The target would be the minimum percentage conformity such as 90%. Similarly, the recommendation may be that pneumothoraces after lung biopsy should not exceed 15% at 1 h post-procedure.

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The indicator would be the number of patients with a pneumothorax on a chest film taken at 1 h post-procedure, and the initial target might be 20%. The standard will indicate ideal expectation, the indicator signifies reality, and the target gives the required minimum achievable result locally, perhaps during the development period of the biopsy service.

Numbers for audit As mentioned in the section on audit and research, large numbers are not necessary for a successful audit and may indeed lead to failure of completion of the audit cycle. The choice of sample size can be difficult and should be decided for each individual circumstance.The number of cases or episodes audited should reflect the number seen locally in practice. There is no need for controls. In audits where a high percentage compliance is required (e.g. 100%) a relatively small sample might show failure of compliance early on (even after review of the first case). It may be that in an audit of a high risk, low frequency activity (e.g. percutaneous nephrolithotomy), the preference may be to include all cases for audit prospectively, running the audit as a continuous process, reviewing results on a month-by-month, or year-by-year basis, in order to show trends. For a higher frequency clinical activity, it may be decided to review only a randomly chosen 5% sample of cases or reports within the audit (e.g. double reporting of CT staging scans in cases of lung cancer). The error rate in reporting can be a useful audit process to improve the quality of report content and structure37. Audit of even a low number of cases may indicate that there is a cause for concern and that further work is required. It is important not to draw premature conclusions without considering all the factors influencing the initial audit outcome. An excellent analysis of numbers in audit is available in a RCR governance publication (see Suggested Further Reading).

Implementing change and re-audit The most difficult, but also the most satisfying aspect of audit, is the successful implementation of any required or recommended change. The change required will depend upon local circumstances, available resources, and a willingness to adopt change in practice. The most important aid to introducing change is the acceptance by those involved in the audit of the need for change, should the audit show a failure to reach target. It is also essential to involve and inform those with the authority to introduce (and fund) change, and identify and empower those who will implement the changes. It has been shown that when the real cost of carrying out an audit is known to managers and clinicians, the recommended changes are more likely to be implemented38. Clinical audit can be a powerful force in the process of introducing new techniques, managing staff development and creating improved services and circumstances for staff and patients. As a business tool, it can be a two-edged sword, not only identifying poor performance but also supplying the evidence of need where resource inadequa-

cies exist39,40. The date by which any changes should have been introduced must be made clear and also the date by which any second audit will be carried out. Re-audit is an essential part of the process in order to demonstrate that the changes have really produced the expected improvements. To these ends, it is essential to create written reports of any audits carried out, with the associated recommendations for change clearly stated. Circulate these effectively and use them in the clinical governance report to the directorate and Trust. These actions will make the results and the process for change explicit and available as part of the governance process, and available for review. Here we come to the important matter of confidentiality.

Confidentiality In the collection of data during the audit process, details about patients and clinicians will be identified. If this information is available within the public domain, clinicians will inevitably become less willing to give further information and to cooperate. Although the results of audit need to be available to those with a legitimate interest in generating high clinical standards (Trusts, Royal Colleges, managers, purchasers and patients), such results should be of a general nature rather than person specific. Such person-specific audit information needs to be protected. There is, of course, a requirement that a responsible individual within each Trust (usually the Medical Director) has access to information relating to any one individual or group. This is particularly important where matters of clinical performance are brought into question. The GMC recommends that patient data should be kept anonymous for the protection of individuals41.

ACHIEVING SUCCESSFUL ORGANIZATION OF AUDIT The essential requirements for successful departmental audit are time, facilities, clarity of organization and responsibility, multidisciplinary involvement and a readiness to accept change. An absence of any of these, particularly time42, makes the achievement of successful audit much more difficult. Time allocation for audit work and meetings to receive and discuss results is essential. It is part of the agreed job plan for doctors under the new NHS contract introduced in 2003 and should be achievable and acceptable to the directorate. Advice and help with data collection and IT support are present within all Trusts, funding having been allocated for audit staff. Each department requires a clearly identifiable leader for audit with the responsibility to organize meetings, coordinate appropriate audits and create an annual audit report to the Trust43. The audit leader is also supported by the RCR audit subcommittee. Opportunities should be sought for cross-specialty audit and the creation of multidisciplinary care pathways with agreed standards.

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All staff groups should ideally be included within the audit processes and consideration must also be given to inclusion of patients in the audit process44.

THE RE-LAUNCH OF AUDIT It is well recognized that since its launch in the UK, the expected improvements in clinical practice from clinical audit have not materialized, despite major investment and work by many to facilitate its acceptance. One reason for this is the tendency for medical staff to see audit as a time-consuming process separate from the rest of their clinical activities, rather than as an integrating tool to show what they are achieving and what resources they need. The bulk of the work is often left to junior medical staff or radiographers who do have a role to play as team members. Furthermore, there may well be different agendas and priorities held by clinicians and managers. With the requirement to develop real clinical governance, and the responsibility for quality of care now clearly lying with chief executives, we may now see the tool of audit being used more coherently with less divergence of opinion and priority45. The development of multidisciplinary working and clear standards of care and process in recent years should make it easier to identify effective and reproducible audit processes that can be shared nationally and allow comparison of outcomes and methods over the whole National Health Service.

REFERENCES 1. Department of Health 1997 The new NHS: modern, dependable. The Stationery Office, London 2. Dobson F 1998 A first class service: quality in the new NHS. Government White Paper 35. The Stationery Office, London 3. Scally G, Donaldson L J 1998 Clinical governance and the drive for quality improvement in the new NHS in England. Br Med J 317: 61–65 4. Royal College of Radiologists 1999 Good practice guide for clinical radiologists. RCR, London 5. Royal College of Radiologists 2003 Making the best use of a department of clinical radiology: guidelines for doctors, 5th edn. RCR, London 6. Royal College of Radiologists 1999 Workload and manpower in clinical radiology. RCR, London 7. Royal College of Radiologists 2000 Clinical governance and revalidation: a practical guide for radiologists. RCR, London 8. Royal College of Radiologists 1999 Skills mix in clinical radiology. RCR, London 9. General Medical Council 2001 Good medical practice. GMC, London 10. Royal College of Radiologists 1996 Advice to clinical radiology members and fellows with regard to out of hours working. RCR, London 11. Panting G 1999 Where do we stand on informed consent? Continuing Medical Education Journal: Radiology Update 1: 29–31 12. General Medical Council 1999 Seeking patients’ consent: the ethical considerations. GMC, London 13. Royal College of Radiologists 1999 Guidance on consent by patients to examination or treatment in a Department of Clinical Radiology. RCR, London 14. Royal College of Radiologists 2002 Risk management in clinical radiology. RCR, London

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15. General Medical Council 2003 A licence to practise and revalidation. GMC, London 16. Royal College of Radiologists 2004 Individual responsibilities—a guide to good medical practice for clinical radiologists. RCR, London 17. Shipman Inquiry 2004 Fifth report—Safeguarding patients: lessons from the past, proposals for the future. HMSO website: www.theshipman- inquiry.org.uk/fifthreport.asp 18. Smith R 2005 The GMC: expediency before principle. Br Med J 330: 1–2 19. National Institute for Clinical Excellence (NICE) 2002 Principles for best practice in clinical audit. Radcliffe Medical Press, Oxford 20. Department of Health 2000 Harold Shipman’s clinical practice 1974–1998: a review commissioned by the Chief Medical Officer. The Stationery Office, London 21. Lanier D C, Roland M, Burstin H, Knottnerus J A 2003 Doctor performance and public accountability. Lancet 362: 1404–1408 22. Secretaries of State for Health, Wales, Northern Ireland and Scotland 1989 Working for patients. Working Paper 6: Medical audit. HMSO, London 23. Nightingale F 1863 Notes on hospitals, 3rd edn. Longman Green/ Longman, Roberts and Green, London, p 63 24. American College of Surgeons 1924 The minimum standard of the American College of Surgeons’ hospital standardisation program. Bull Am Coll Surgeons 8: 4 25. Joint Commission on Accreditation of Hospitals 1975 Supplement to the accreditation manual for hospitals. JCAH, Chicago 26. Department of Health 2000 The NHS plan: a plan for investment, a plan for reform. The Stationery Office, London 27. Fowkes F R G 1982 Medical audit cycle. A review of methods and research in clinical practice. Med Educ 16: 228–238 28. Donabedian A 1966 Evaluating the quality of medical care. Milbank Mem Fund Q 44: 166–206 29. Godwin R J, DeLacey G, Manhire A (eds) 1996 Clinical audit in radiology: 100+ recipes. RCR, London 30. Donabedian A 1988 The assessment of technology and quality. A comparative study of certainties and ambiguities. Int J Technol Assess Health Care 4: 487–496 31. Royal College of Radiologists Working Party 2003 Making the best use of a Department of Clinical Radiology: guidelines for doctors, 5th edn. RCR, London 32. McCreath G T, O’Neill K F, Kincaid W C, Hay L A 1999 Audit of chest X-rays in general practice: a case for local guidelines? Health Bull 57: 180–185 33. Godwin R 1995 Nothing succeeds like success—some do’s and don’ts in clinical audit. Clin Radiol 50: 818–820 34. Jackson G 1997 Clinical audit—KISS is better. Int J Clin Pract 51: 83 35. DeLacey G, Godwin R J, Manhire A R (eds) 2000 Clinical governance and revalidation. RCR, London 36. Shaw C 1989 Medical audit: a hospital handbook. King’s Fund Centre, London 37. Peters M A, Bomanji J, Costa D C et al 2004 Clinical audit in nuclear medicine. Nucl Med Commun 25: 97–103 38. Tomalin D, Renshaw M 1999 Clinical audit. Count the cost. Health Serv J 109: 28–29 39. DeLacey G 1995 Don’t look a gift horse in the mouth. Clin Radiol 87: 815–817 40. Jackson S 1999 Achieving a culture of continuous improvement by adopting the principles of self assessment and business excellence. Int J Health Care Qual Assur Inc Leadersh Health Serv 12: 59–64 41. General Medical Council 2004 Confidentiality: protecting and providing information. GMC, London 42. Manhire A, Cook A, Adam J et al 1998 Audit in radiology: a survey of hospital departments in the UK. Health Trends 30: 72–77 43. Renshaw M, Ireland A 2003 Specialty audit leads: has this concept been effective in implementing clinical audit in an acute hospital? Int J Health Care Qual Assur Inc Leadersh Health Serv 16: 136–142 44. Avis M 1997 Incorporating patients’ voices in the audit process. Qual Health Care 6: 86–91 45. Berger A 1998 Why doesn’t audit work? Br Med J 316: 875–876

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SUGGESTED FURTHER READING: CLINICAL AUDIT DeLacey G, Godwin R J, Manhire A R (eds) 2000 Clinical governance and revalidation. RCR, London Dixon N 1996 Good practice in clinical audit—a summary of selected literature to support criteria for clinical audit. National Centre for Clinical Audit, London

Godwin R J, DeLacey G, Manhire A (eds) 1996 Clinical audit in radiology: 100+ recipes. RCR, London National Institute for Clinical Excellence 2002 Principles for best practice in clinical audit. Radcliffe Medical Press, Oxford

CHAPTER

Techniques in Thoracic Imaging

11

Zelena A. Aziz and David M. Hansell

• • • • • • • •

Chest radiography Computed tomography High-resolution computed tomography Ultrasound Magnetic resonance imaging Ventilation–perfusion scintigraphy Positron emission tomography Positron emission tomography–computed tomography

Chest radiography and computed tomography (CT) are the two most important imaging tests used to evaluate respiratory disease. The basic technique of chest radiography has changed little over the past 100 years but recent developments in image receptor technology have resulted in the more efficient acquisition of chest radiographs with the benefit of a lower radiation dose. These images are produced in digital format, so facilitating their incorporation into picture archiving and communications systems (PACS). Advancing CT technology has meant that multidetector row CT (MDCT) systems have largely replaced single-detector CT. The resultant increase in data acquisition speed and z-axis spatial resolution has meant that volumetric high-resolution acquisitions are increasingly becoming the norm. Protocols for MDCT continue to be developed and refined, and currently, particular attention is being directed at dose-reducing strategies. The recent development of fused CT–positron emission tomography (PET) images has revolutionized the investigation of patients with suspected neoplastic disease, enabling the simultaneous assessment of both metabolic function and anatomical location.The role of other imaging techniques such as magnetic resonance imaging (MRI) and ultrasound (US) is limited to specific clinical situations and this is likely to remain the case given the obvious capabilities of MDCT.

CHEST RADIOGRAPHY Many chest radiographs are still acquired with conventional film–screen radiography systems that provide, at low cost,

good image quality and high spatial resolution1,2. However, the disadvantages of film–screen radiography are a limited exposure range, a relatively high retake rate and inflexibility of image display and manipulation1. As computer technology and storage capacities have developed over recent years, the considerable advantages of digital imaging systems and of PACS have become increasingly evident. As a result, digital imaging systems are now commonplace in radiology departments. Early digital imaging systems used a photostimulable phosphor image receptor plate (generally termed ‘computed radiography’ [CR]); these CR systems continue to be widely used because of their compatibility with existing radiography equipment. The phosphor plate stores some of the energy of the incident X-ray as a latent image. On scanning the plate with a laser beam, the stored energy is emitted as light that is detected by a photomultiplier and converted to a digital signal. The digital information is then manipulated, displayed and stored in whatever format is desired. More recently, full-field digital amorphous silicon flat-panel X-ray detector radiography systems based on caesium iodide and amorphous silicon have become commercially available. These thin film transistor (TFT) flat-panel detector systems (also referred to as DR [direct radiography]) are now widely available.The advantages of this technology include high detection efficiency and rapid image display.These systems have excellent image quality3,4 and allow a significant reduction in effective dose compared with either conventional film–screen or storage phosphor based CR systems5. Digital radiography systems have many advantages over conventional radiography: the photostimulable phosphor plate is reusable, user controlled post-processing is automatically performed to generate the display features desired for the anatomical part selected, and there is more efficient image archiving, retrieving and transmission. One of the most important advantages over conventional radiography is the wide dynamic range or latitude of the image plate—consequently, exposure errors are reduced and the need for repeat examinations is lessened.

Additional radiographic views Frontal and lateral projections are adequate for most purposes. Other radiographic views are less frequently performed

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• THE CHEST AND CARDIOVASCULAR SYSTEM

because of the ready availability of cross-sectional imaging. One projection that is occasionally used is the lateral decubitus view, taken as a frontal projection with a horizontal beam and the patient lying on his/her side. Its main purpose is to identify an effusion that is not visible on an erect chest radiograph, or to demonstrate the movement of fluid in the pleural space.The lateral decubitus view is recommended by American Thoracic Society (ATS) guidelines for all patients presenting with community-acquired pneumonia; the rationale being that if the thickness of the effusion on the lateral decubitus view is < 1 cm, the effusion is small enough not to require further intervention6 (in practice this guideline is studiously ignored).The contrary view is that a parapneumonic effusion large enough to be potentially clinically significant can usually be defined by postero-anterior (PA) and lateral radiographs, and that if loculations are suspected, then CT will define the pleural space more accurately than a lateral decubitus radiograph7. Occasionally the lateral decubitus radiograph can confirm the presence of small amounts of fluid if there is a subpulmonic effusion or if the costophrenic angles are obscured by a pulmonary infiltrate. Radiographs exposed in expiration are valuable in the investigation of air trapping, particularly in paediatric practice in the context of a suspected inhaled foreign body. An expiratory radiograph may also enhance the demonstration of a small pneumothorax.

Portable chest radiography The imaging problems associated with portable chest radiography are (A) scattered radiation; (B) the inability of the radiograph to capture all relevant information; and (C) the lack of control over the overall optical density of the resulting image when there is slight over- or under-exposure. Additionally, the shorter focus–film distance results in undesirable, and sometines misleading, magnification of structures. High kilovoltage techniques cannot be used because portable machines are unable to deliver a sufficiently high kilovoltage, and as the maximum current is limited, long exposure times are needed, increasing movement artefact.The development of CR systems has provided solutions to some of the limitations of portable chest radiography by controlling optical density and contrast, but it does not eliminate the problem of scatter. Though their instant readout capabilities would be a great advantage at the bedside, DR detectors are not applicable to portable work, largely due to cost considerations. Therefore, it is expected that storage phosphors will continue to be the media of choice for portable radiography for some time to come.

COMPUTED TOMOGRAPHY The introduction of spiral (helical) CT in the early 1990s constituted a fundamental evolutionary step in the ongoing refinement of CT imaging, replacing the discontinuous acquisition of data in conventional CT with volumetric data acquisition. In 1998 several CT manufacturers introduced MDCT systems, which provided considerable improvement in data acquisition speed and longitudinal resolution, and more efficient use of X-rays8–10. These systems typically offered simultaneous

acquisition of four sections with a gantry rotation time of 0.5 s. Since then, there has been further rapid improvement in scanner performance with increased numbers of detector rows and faster tube rotation; currently, systems with 16-, 32-, 40- and 64-active detector rows are available. Rotation times of the X-ray tubes have decreased from 0.5 s to 0.33 s per rotation. The faster data acquisition enables not only better coverage in a single breath-hold, but also results in a significant reduction in patient movement artefacts. In paediatric practice this has meant less frequent need for sedation11. The introduction of MDCT has expanded the clinical indications for CT; these are summarized in Table 11.1. With MDCT systems, different section widths are achieved by collimating and adding together the signals of neighbouring detector rows. The Somatom Sensation 4 system (Siemens, Forchheim), for example, uses the adaptive array detector design and has eight detector rows. Their widths in the longitudinal direction range from 1 to 5 mm at the isocentre and this arrangement allows the following collimated section widths: two sections at 0.5 mm, four at 1 mm, four at 2.5 mm, four at 5 mm, two at 8 mm and two at 10 mm. Currently, there is a trend amongst thoracic radiologists towards acquiring high-resolution (1–1.25-mm thickness) volumetric images which can then be reconstructed at 1.25–5-mm intervals for interpretation depending on the clinical question. Hence, from the same dataset, both narrow sections for high spatial resolution detail or three-dimensional (3D) post-processing, and wide sections for better contrast resolution or quick review, can be derived.The convenience of a single protocol is particularly useful for patients with suspected focal and interstitial lung disease. Thin section reconstructions are recommended for volumetric assessment12 and characterization13 of pulmonary nodules, the evalution of interstitial lung disease and the evaluation of pulmonary embolism14, whereas 3–5-mm reconstructions are usually adequate for the initial assessment of mediastinal masses and for lung cancer staging studies. In younger patients, however, a more critical approach

Table 11.1

INDICATIONS FOR CT OF THE CHEST

In the acute setting Chest trauma Evaluation of acute aortic syndromes (dissection, transection) Demonstration of pulmonary embolism Identification of complications post thoracic surgery (mediastinal haematomas, complex pleural collections) In the nonacute setting Further evaluation of nodules, hilar or mediastinal masses identified on a chest radiograph Lung cancer diagnosis and staging Assessment of congenital anomalies of the thoracic great vessels Characterization of interstitial lung disease Identification of bronchiectasis/small airways disease Detection of pulmonary metastases from known extrathoracic malignancy

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should be adopted with the CT examination being tailored to the specific clinical question being asked, to avoid unnecessary radiation dose. The introduction of 16- and 64-detector MDCT systems has allowed the goal of truly isotropic imaging to be realized. Here, each image data element (voxel) is of equal dimensions in all three spatial axes, and forms the basis for image display in any arbitrarily chosen imaging plane. The acquisition of volumetric high-resolution data has particularly revolutionized the noninvasive assessment of vascular disease in the chest, and also paved the way for the further development of more sophisticated 3D image processing techniques. Many anatomical features of the chest do not conform to a single two-dimensional (2D) axial plane and full exploitation of isotropic MDCT data requires 2D and 3D post-processing techniques to harness the added advantage of improved z-axis resolution and coverage. Table 11.2 summarizes the main post-processing techniques used in evaluating chest disease.

Definition of spiral pitch An important parameter for characterizing helical CT is the pitch, which according to International Electrotechnical Commission specifications is defined as p = TF/W, where TF is the table feed per rotation and W is the total width of the

Table 11.2

• TECHNIQUES IN THORACIC IMAGING

collimated beam.15 With four sections at 1-mm collimation and a table feed of 6 mm per rotation, the pitch is p = 6/(4 × 1) = 1.5. This definition holds true for both single- and multidetector row CT systems. In the early days of four-detector CT, the term detector pitch was introduced, which accounted for the width of a single section in the denominator. For the sake of uniformity, the term detector pitch should no longer be used16.

Dose considerations Despite the undisputed clinical benefits of MDCT, there is the issue of increased radiation compared to single-detector CT to consider. In a CT X-ray tube, a small area on the anode plate emits X-rays that penetrate the patient and are registered by the detector. A collimator between the X-ray tube and the patient, the pre-patient collimator, is used to shape the beam and establish the dose profile. In general, the collimated dose profile is a trapezoid in the longitudinal direction. In the umbral region, X-rays emitted from the entire area of the focal spot fall on the detector; however, in the penumbral regions, only a part of the focal spot illuminates the detector—the pre-patient collimator blocking off other parts. With single-detector CT, the entire trapezoidal dose profile can contribute to the detector

POST-PROCESSING TECHNIQUES THAT MAY BE APPLIED IN EVALUATING CHEST PATHOLOGY

Post-processing technique

Technical considerations

Clinical applications

Multiplanar and curved multiplanar reconstructions (MPR and CMPR)

2D techniques that provide alternate viewing perspectives, usually with conventional window settings. Images are obtained by a reordering of the voxels into 1 voxel-thick tomographic sections, excluding those voxels outside the imaging plane

Evaluation of the large airways and pulmonary emboli, particularly for interpretative difficulties on axial sections either due to partial volume averaging or the inability to differentiate periarterial from endoluminal abnormalities

Maximum intensity projection (MIP)

A ray is cast through the CT data and only data that are above an assigned value are displayed, thus reducing all data in the line of the ray to a single plane. Sliding slabs of 5–10 mm are commonly used

Main use is in vascular imaging (Fig. 11.1) and in the evaluation of micronodular disease (more accurate identification of nodules versus vessels, and more precise characterization of nodule distribution)

Mininum intensity projection (MinIP)

Similar to MIP, but only data below an assigned value are displayed and thus it is best suited for showing areas of low density

May improve conspicuity of subtle density differences of lung parenchyma and therefore highlight regions of emphysema or air trapping

Shaded surface display (SSD)

This technique reformats data around a threshold that defines the interface of tissues. SSD does not reveal any internal detail

Evaluation of airway abnormalities

Volume rendering

Volume rendering is a unique form of 3D visualization. In this process a ray is projected through the dataset and a weighted representation of all the Hounsfield units encountered is displayed depending on their representation within the tissues. Voxels that are only partially filled with a density of interest are also included. The resultant images contain depth information whilst maintaining 3D spatial relationships

Used in angiographic examinations and also to evaluate large airway abnormalities (Fig. 11.2)

‘Virtual bronchoscopy’

Surface rendering and volume rendering are used to produce endoscopic simulations of the airway (Fig. 11.3)

Virtual endoscopic or perspective volume rendering images are not widely applied as they seldom give information that cannot be obtained by MPR. However, virtual CT bronchoscopy used in association with 3D techniques providing extraluminal information can provide additional information such as safe routes for tracheobronchial biopsy. Monitoring the position of airway stents is another potential application of this technique

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Figure 11.1 Maximum intensity projection (MIP) in vascular imaging. MIP reconstructed using 5-mm slabs demonstrates a markedly tortuous thoracic aorta. The descending thoracic aorta is aneurysmal with extensive mural thrombus.

signal, and thus the relative dose utilization of a single-detector CT system can be close to 100%. With MDCT, only the plateau region of the dose profile is used to ensure an equal signal level for all detector elements. The penumbral region is then discarded, either by a post-patient collimator or by the intrinsic self-collimation of the MDCT, and represents ‘wasted’ dose. The relative contribution of the penumbral region decreases with increasing section width and with an increasing number of simultaneously acquired images (Fig. 11.4). Thus, the relative

dose utilization with four-section 1-mm collimation CT is 70% or less depending on the scanner type, whereas with 16-section CT systems, dose efficiency can be improved to 84%. The CT parameters that affect radiation dose include gantry geometry, tube current and voltage, acquisition modes, collimation, pitch and gantry rotation time. Reduction in tube current is the most practical means of reducing CT radiation dose. A 50% reduction in tube current can halve effective radiation dose17. Authors of several studies using MDCT have suggested that it is possible to reduce tube current markedly (to between 40 and 70 mAs) in chest examinations without affecting image quality18,19. On a 64-detector MDCT, the dose for a volumetric high-resolution (1-mm sections) acquisition of the thorax in a 70 kg adult can be as low as 3.6 mSv if parameters of 120 kVp and 90 mAs (pitch of 1) are used (E. Castellano-Smith, personal communication). In lung cancer screening examinations, tube current can be remarkably low and yet yield images of diagnostic quality. Itoh et al have shown that images obtained at an effective tube current of 20 mAs are of equal diagnostic utility to those obtained at 50 mAs for the detection of 6-mm simulated nodules20. Another recommendation comprises acquisition of the entire chest using a 1-mm collimation (MDCT) at 120 kVp and 10–40 mAs depending on the body habitus of the individual21. At a tube current of 10 mAs, the effective radiation dose is 0.27 mSv; equivalent to just five conventional PA chest radiographs. In the paediatric population, some institutions favour the use of 1 mAs kg−1 for imaging the thorax; an approach that significantly reduces radiation dose. Tube potential (peak voltage) determines the incident X-ray mean energy, and variation in tube potential causes a substantial change in CT radiation dose. The effect of tube voltage on image quality is complex, since it affects both image noise and

Figure 11.2 Volume rendering to evaluate large airway abnormalities. (A) The axial image of a patient with recurrent adenoid cystic carcinoma shows narrowing of the right main bronchus with abnormal soft tissue surrounding the right upper lobe bronchus. (B) The volume rendered 3D image enables the entire extent of the stenosis to be visualized on a single image.

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Figure 11.3 ‘Virtual bronchoscopy’ of the airway. (A) Axial CT and (B) virtual bronchoscopic rendition demonstrating a carcinoid tumour protruding into the lumen of the distal trachea just above the level of the carina.

tissue contrast.Thus, the image quality ramifications of a decrease in tube voltage to reduce radiation exposure must be carefully examined before being implemented. For chest examinations, 120 kVp is commonly used. In thin patients (< 50 kg) and in the paediatric population, 100 kVp is recommended; the use of 80 kVp has been found to be associated with unacceptable beam hardening even in the smallest of patients (Fig. 11.5)22. With helical CT systems, beam collimation, table speed and pitch are interlinked parameters that affect diagnostic image quality. Faster table speed for a given collimation, resulting in a higher pitch, is associated with a reduced radiation dose (if other data acquisition parameters, including tube current, are held constant) because of a shorter exposure time. However, this is not true for some multidetector systems that use an effective milliampere–second setting (defined as milliampere seconds divided by pitch). Here, the effective milliampere–second level is held constant (by automatic tube current adjustment) irrespective of pitch value, so that radiation dose does not vary as pitch is changed23. Caution should be exercised when extrapolating dose reduction strategies from single- to multi-detector CT systems.

4–slice collimator

CT

detector

16 – slice collimator

CT

Automatic tube current modulation is a technical innovation that can substantially reduce patient dose.There are two methods used currently with CT systems: z-axis modulation and angular (x- and y-axis) modulation. In z-axis modulation, tube current is adjusted to maintain a user-selected quantum noise level in the image data. z-axis modulation attempts to render all images with similar noise, independent of patient size and anatomy. In angular modulation, the tube current is adjusted to minimize X-rays in projections (angles) that have less importance for the reduction of overall image noise content. With this technique, the tube output is adapted to the patient geometry during each rotation to compensate for strongly varying X-ray attenuation in asymmetric body regions such as the shoulders. A recent investigation of CT imaging studies in children in whom angular modulation was used demonstrated a mean reduction of 22% in dose without loss of image quality24. Ultimately, the complexity of the interrelationships between the different CT parameters and dose requires a close collaboration between radiologists and medical physicists to ensure that the radiation burden to patients is as low as possible without diagnostic accuracy being compromised.

Figure 11.4 Dose profiles for 4- and 16detector MDCT. The relative contribution of the penumbral region (P), representing wasted dose, decreases with increasing number of simultaneously acquired sections.

detector

Umbra

P

Detectors

P

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sibly a reduced volume. Typical injection parameters for fourdetector MDCT are 100–150 ml of 240–320 mg ml−1 of iodine injected at a rate of 3–4 ml s−1. For 64-detector MDCT, some institutions have experimented with 90–120 ml of 320–370 mg ml−1 of iodine injected at 3.5–5 ml s−1. A recent study using a four-detector system evaluated the influence of iodine flow concentration on vessel attenuation29. There was significantly better visualization of fourth-, fifth- and sixth-order pulmonary arteries using a protocol based on 90 ml of 400 mg ml−1 of iodine when compared with 120 ml of 300 mg ml−1. An injection rate of 4 ml s−1 was used in both groups. A specific application of contrast enhancement is in the differentiation between benign and malignant pulmonary nodules and the reader is referred to two papers for details of this protocol30,31.

Window settings

Figure 11.5 Image obtained at 80 kVp on a 64-detector MDCT in a 1-year old with cough. Right lower lobe collapse is identified but the image is unacceptably noisy, making evaluation of the lung parenchyma difficult.

Intravenous contrast medium enhancement The following section will cover the basic principles of intravenous enhancement as applied to the evaluation of pulmonary disease. Intravenous enhancement is used routinely for CT angiography of the thorax; the most common indications being the evaluation of the pulmonary arterial tree in suspected pulmonary embolism, the aorta and lung cancer staging studies. Intravenous enhancement is influenced by several factors: body size and cardiac output of the patient, the concentration and volume of contrast material, the rate and duration of the injection, the delay between the injection and the initiation of data acquisition, the duration of data acquisition and whether bolus tracking or a set delay is used. With single-detector CT, protocols are relatively straightforward. A volume of 100 ml of 150 mg ml−1 of iodine injected at a rate of 2.5 ml s−1 after a 25-s delay is recommended for general thoracic work25. Suggested protocols for evaluating the pulmonary arterial tree using single-detector CT use between 120 and 140 ml of 240–300 mg ml−1 of iodine injected at a rate of 3–4 ml s−1 26,27 with either a fixed delay of 20 s28 or the use of automated triggering mechanisms. With advances in CT technology, however, the way contrast medium is delivered has had to be rethought. A CT study acquired using a 16-detector system in < 10 s leaves little room for error, and imaging at peak enhancement requires not only precise timing but careful tailoring of the volume and rate of delivery of contrast medium. One dilemma for fast CT is the chance of contrast medium still being injected when data acquisition is complete. Protocols for CT angiography of the chest using MDCT are still being refined, but it is generally accepted that the faster acquisition times of MDCT require a faster rate of injection, a higher concentration of contrast medium and pos-

The density within each voxel is represented by a Hounsfield unit (HU) value. In the thorax these units encompass a wide range, from aerated lung (approximately −800 HU) to ribs (+700 HU). No single-window setting can depict this wide range of densities on a single image. For this reason, a thoracic CT examination requires viewing in at least two settings in order to demonstrate the lung parenchyma and the soft tissues of the mediastinum. Furthermore, it may be necessary to adjust the window settings to improve the demonstration of a particular structure or abnormality. Preferred window settings for thoracic CT vary between institutions, but some generalizations can be made. For the soft tissues of the mediastinum and chest wall a window width of 300– 500 HU and a centre of +40 HU are appropriate. For the lungs a wide window of approximately 1500 HU or more at a centre of approximately −600 HU is usually satisfactory. The window settings have a profound influence on the visibility and apparent size of normal and abnormal structures. The most accurate representation of an object appears to be achieved if the value of the window level is halfway between the density of the structure to be measured and the density of the surrounding tissue. For example, the diameter of a pulmonary nodule, measured on soft tissue settings appropriate for the mediastinum, will be grossly underestimated31. It is also important to remember that when inappropriate window settings are used, smaller structures (e.g. peripheral pulmonary vessels) are proportionately much more affected than larger structures.

HIGH-RESOLUTION COMPUTED TOMOGRAPHY For the majority of patients being investigated exclusively for suspected interstitial lung disease, interspaced (as opposed to volumetric) high-resolution CT (HRCT) remains an adequate examination and should be used for younger patients. This is because the dose of interspaced HRCT is considerably lower than a volumetric high-resolution acquisition. Even when techniques are optimized for dose, volumetric HRCT of the chest incurs a dose that is at least three times higher than interspaced HRCT, and in certain cases the dose

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increase can be up to 10-fold, particularly if a relatively high milliampere–second setting (170 mAs) is used32.The fundamental components of an HRCT technique include thin collimation, usually 1–2 mm, coupled with a high spatial frequency algorithm reconstruction. Thin collimation improves spatial resolution and consequently enhances the detection of key morphologic features in HRCT interpretation: thickened interlobular septa, ground-glass opacification, small nodules and abnormally thickened or dilated airways. Reducing the section thickness below 1 mm will not yield any significant further improvement in spatial resolution and at the same time will reduce the signal-to-noise ratio of the image. A sharp reconstruction algorithm reduces image smoothing and makes structures visibly sharper, although image noise becomes more obvious33. Images are usually obtained in the supine position from the apices to the lung bases at full inspiration and at 10- or 20-mm intervals. When early interstitial fibrosis is suspected, HRCT is often performed in the prone position to prevent confusion with the increased opacification often seen in the dependent posterobasal segments in the usual supine position (Fig. 11.6). However, there is no advantage in prone CT if there is obvious diffuse lung disease on a contemporary chest radiograph34. Prone CT is mandatory in the evaluation of asbestosis in which subtle parenchymal abnormalities are most frequently seen in the caudal parts of the posterobasal segments (Fig. 11.7)35. The necessity of expiratory CT sections is somewhat controversial. In most patients with clinically significant small airways disease, the mosaic attenuation pattern attributable to small airways disease is apparent on inspiratory images. However, images obtained at end-expiration can certainly accentuate the regional heterogeneity of lung density, thus revealing small or subtle areas of air trapping (Fig. 11.8)36,37.

• TECHNIQUES IN THORACIC IMAGING

ULTRASOUND The main advantages of chest ultrasonography are its bedside availability, absence of radiation and the ease of guided aspiration of pleural fluid and some solid tumours. Visualization of the chest wall requires a high frequency linear probe (5– 7.5 MHz), whereas pleural and pulmonary pathology is better detected with a sector or phased-array probe with a lower frequency (3.5 MHz). Most pleural fluid collections of clinical significance are readily identified on standard chest radiographs, but in the intensive care setting even small effusions may cause respiratory compromise and ultrasound (US) is an effective way of detecting and subsequently guiding aspiration. US is also valuable for identifying septations within loculated collections which may influence the choice of treatment38. With real-time US, the movement of the diaphragm may be observed and the reduced motion of paralysis may be of diagnostic value. US is also a quick and effective way of guiding percutaneous needle biopsy of peripheral lung, pleural or chest wall lesions39, but cannot be used if there is any aerated lung between the ultrasound probe and the lesion. An early study reported a potential use of US in diagnosing chest wall invasion in lung cancer staging (disruption of the pleural line which is normally seen as an echogenic interface), but this technique has not become widely used40.

Endoscopic ultrasonography Endoscopic ultrasonography (EUS) is a unique investigation in which a high-frequency US transducer is incorporated into the tip of an endoscope to provide high-resolution images of the gastrointestinal wall and structures in close proximity to the gastrointestinal tract. Linear echoendoscopes that can image parallel to the long axis of the instrument allow visualization

Figure 11.6 HRCT for suspected interstitial fibrosis. (A) Supine HRCT image of a patient being investigated for suspected interstitial lung disease reveals increased opacification in the posterior aspects of both lower lobes, which completely resolve with the patient prone (B).

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Figure 11.7 HRCT for suspected asbestosis. (A) HRCT image in the supine position demonstrates fine reticulation and increased subpleural density (arrows). (B) These changes (arrows) persist on the prone image and may represent early asbestosis in this patient who had an appropriate asbestos exposure.

Figure 11.8 (A) Inspiratory and (B) end-expiratory HRCT images in a patient with known hypersensitivity pneumonitis. There is evidence of a subtle mosaic attenuation on the inspiratory image but this is made much more conspicuous on the end-expiratory image revealing spared secondary pulmonary lobules.

of a projecting needle, relative to adjacent tissue, making EUSguided aspiration or intervention possible. Transoesophageal EUS-guided real-time fine-needle aspiration (FNA) of mediastinal lymph nodes has become a useful, minimally invasive and safe method for staging the mediastinum41–43. In patients with non-small cell lung cancer (NSCLC) who have enlarged mediastinal nodes on CT, the accuracy of EUS-guided FNA is approximately 96%43. EUS-guided FNA is particularly suited for posterior mediastinal staging, with enlarged lymph nodes in the subcarina, aortopulmonary window, para-oesophageal area and para-aortic area. EUS can also play a significant role in identifying patients with unresectable (N3) NSCLC when adenopathy was not present on CT44. The importance of histological confirmation by EUS–FNA is emphasized as echo characteristics alone are not adequately sensitive to predict malignancy.

MAGNETIC RESONANCE IMAGING General technical considerations of magnetic resonance imaging (MRI) are outlined elsewhere and its specific applications in the chest are described where appropriate in the succeeding chapters. Accumulated evidence has demonstrated that MRI is no substitute for CT in the investigation of most thoracic conditions that require cross-sectional imaging; this is largely due to the relatively poor spatial resolution of MRI, the extremely low proton density of normal lung, the further decrease of signal by strong susceptibility artefacts induced by the multiple air–soft tissue interfaces within the lung, and the consequences of cardiac and respiratory movement. The advent of MDCT has allowed the acquisition of high-resolution thin sections and with this, the ability to produce multiplanar reconstructions. Consequently, MDCT is used for most aspects of thoracic

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imaging, including areas thought previously to be the domain of ‘problem-solving’ MRI. The main indications for MRI in the chest include the evaluation of the heart and great vessels, characterization of mediastinal lesions that are equivocal on CT, evaluation of superior sulcus tumours, particularly if brachial plexus involvement is suspected, and in demonstrating pulmonary embolism if radiation and intravenous contrast medium need to be avoided. This section will summarize the spectrum of MRI techniques that are used in thoracic imaging. Traditional imaging sequences have included T1-weighted spin echo (SE) with or without the use of gadolinium chelates (for the initial detection of abnormalities or the demonstration of anatomy) and T2-weighted fast spin echo (FSE) (for further characterization of abnormalities). Occasionally, a fatsaturation MRI technique (phase-shift gradient-echo imaging or proton-selective fat-saturation imaging) can be useful to detect fat and distinguish it from haemorrhage in the evaluation of mediastinal masses45. MRI is useful in confirming the cystic nature of mediastinal lesions that appear solid on CT (cysts containing nonserous fluid can have high attenuation on CT) as these cysts will have characteristically high signal intensity when imaged with T2-weighted sequences regardless of the nature of the cyst contents. To overcome the problem of respiratory motion, other sequences (fast low-angle shot [FLASH] and half Fourier turbo-spin echo [HASTE]) have been developed that can be acquired in one breath-hold with acquisition times well below 30 s. Additional techniques to compensate for respiratory motion in non-breath-hold MRI have also been evaluated. These include navigator techniques with registration of the diaphragm, reordering of phase encoding (ROPE) and phase encoding and reordering (PEAR). Recently developed 3D gradient-recalled echo (GRE) sequences for volumetric interpolated breath-hold imaging of the lung may introduce new capabilities for MRI of lung morphology with high spatial resolution46. Early studies indicate that images obtained with this technique provide good visualization of lung anatomy with a low prevalence of artefacts47. The introduction of new lymph node-specific contrast agents used in conjunction with MRI is an interesting development. Ultrasmall superparamagnetic iron oxide nanoparticles traverse the vascular endothelium and are phagocytosed by macrophages in normally functioning lymph nodes. This results in a uniform signal loss in T2- and T2*-weighted images, a feature that was first demonstrated in animal models48. Preliminary data in patients with bronchogenic carcinoma have shown a good sensitivity, but a relatively low specificity for the diagnosis of metastatic normal sized lymph nodes49. Currently, the most important clinical application of MRI is in the imaging of the heart and great vessels, and the specific techniques required for this are dealt with in detail in Chapter 22. In summary, pulse sequences used for cardiac and great vessel imaging can generally be divided into dark or black blood, and bright or white blood imaging techniques. In black blood imaging techniques, rapidly flowing blood is black or of low signal intensity. Examples of this technique include conven-

• TECHNIQUES IN THORACIC IMAGING

tional spin-echo, breath-hold FSE or turbo spin-echo (TSE) variants with double inversion recovery pulses to suppress blood signal (HASTE, double IR TSE–FSE).These techniques are typically used for anatomical delineation of the heart, pericardium, mediastinum and great vessels. In bright blood techniques flowing blood is white or of high signal intensity.These are usually GRE sequences (Fig. 11.9). Cine GRE sequences that produce a motion picture loop throughout the cardiac cycle are used for assessment of cardiac function (and can be used to assess relative motion of adjacent structures in the context of masses abutting vessels or the heart). A single slice multiphase or multislice single-phase acquisition can be performed in a short breath-hold period. Examples of this technique include fast low angle shot (TurboFLASH), fast spoiled

Figure 11.9 (A) Black blood T1 spin-echo image and (B) white blood GRE cine image of the heart. Spin-echo imaging is particularly useful for high-definition anatomical imaging of the heart and vessels, whereas the acquisition of cine loops during a GRE sequence is useful for the assessment of valves and regional contractile function of the myocardium. (Courtesy of Dr Sanjay K. Prasad.)

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GRE, turbo field echo and fast field echo. More recently, faster short TE–GRE sequences with completely refocused gradients have been used to provide excellent contrast between myocardium and blood pool (true FISP, balanced fast field echo, FIESTA). For imaging the intrathoracic vessels, contrast-enhanced MR angiography (MRA) is performed using short, breathhold, 3D T1-weighted GRE sequences (Fig. 11.10). Using the T1-shortening effects of gadolinium-based contrast agents, blood appears bright regardless of flow patterns or velocity. Synchronization of image acquisition and arrival of the contrast bolus is crucial to obtain high image quality. Newer sequences that allow near real-time assessment of a gadolinium contrast bolus are now available, and may be useful for assessment of shunts and fistulas. There is also continued interest in the role of MRA for the diagnosis of pulmonary embolism, either by direct demonstration of the intravascular thrombus50,51 or by decreased signal areas representing underperfused lung on gadolinium-enhanced MRI52. Although still largely a research tool, the introduction of hyperpolarized noble gas imaging using either 3He or 129Xe has been used to demonstrate ventilated parts of the lung53 and

Figure 11.10 3D Gadolinium-enhanced MRA of a patient with aortic dissection. The intimal flap (arrows) is clearly delineated. (Courtesy of Dr Sanjay K. Prasad.)

thus enabled the evaluation of structure–function relationships in lung disease54. Diffusion-sensitive MRI techniques allow mapping of the ‘apparent diffusion coefficient’ (ADC) of 3He within lung spaces, where ADC is physically related to local bronchoalveolar dimensions55. ADC values are increased in fibrosis and emphysema, and show good agreement with predicted lung function56; however, these sophisticated techniques are not widely available.

VENTILATION–PERFUSION SCINTIGRAPHY Ventilation–perfusion (V/Q) scintigraphy is a noninvasive technique for the assessment of the distribution of pulmonary blood flow and alveolar ventilation and has primarily been used for the diagnosis of pulmonary embolism. Perfusion scintigraphy is performed following the intravenous injection of 99m Tc-labelled protein microparticles which, because of their size, undergo micro-embolization in the pulmonary vascular bed. The number of particles injected may range from a minimum of 60 000 to a maximum of 700 000, with the recommended average being 200 000. Because of the theoretical possibility of embolization of a medium-sized systemic vessel, microspheres should be used rather than larger macroaggregates in the presence of a known right-to-left shunt. Krypton-81m is in many ways the ideal agent of choice for ventilation imaging but it has a very short half-life and is expensive to produce. Unlike longer-lived radioactive gases, such as 133Xe, 81mKr does not accumulate progressively in regions of lung with a low ventilatory turnover. The lung can be imaged in multiple projections and in each projection, perfusion and ventilation images can be acquired sequentially, or, with the newer digital cameras, simultaneously. Another commonly used agent for ventilation imaging is 133Xe (half-life of 5.3 d). 133Xe has three advantages over 81mKr: it is cheaper, is readily available in comparison to 81mKr which is available from its generator for 1 d only, and it can be used to detect air trapping. Since the energy of 133Xe is less than that of 99mTc, the ventilation images must be acquired before the 99mTc injection. Furthermore, only one projection is available and, with the lower energy of xenon, the images are of poorer resolution. Other agents include 99mTc-diethylenetriaminepentaacetic or 99mTc-technegas. Technegas is an ultrafine aerosol that is considered to behave truly like a gas due to the mean aerodynamic diameter of the particles being between 30 and 90 nm. The small particle size results in efficiency values of up to 20% (efficiency being defined as the ratio between the amount of applied activity and its actual pulmonary deposition) compared to conventional aerosols which show a degree of efficiency between 1 and 3%. Lung scintigraphy remains part of the diagnostic algorithm in the investigation of patients with pulmonary embolism, and guidelines suggest that it may be considered, subject to its availability, as the initial imaging investigation provided the chest radiograph is normal and there is no significant symptomatic concurrent cardiopulmonary disease57. A recent study evaluating ventilation–perfusion lung scintigraphy performed using SPECT technique (as opposed to

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merely using planar acquisitions) has shown that diagnostic accuracy is comparable with MDCT (four-detector system with 1.25-mm effective slice thickness)58. Analogous to developments in the fields of neurology and cardiology, it can be expected that SPECT will replace planar lung scintigraphy in the near future, but lack of availability will mean that this technique is unlikely to be frequently used for patients with suspected pulmonary embolism.

POSITRON EMISSION TOMOGRAPHY Positron emission tomography (PET) was initially used as a research tool for functional studies of the brain and the assessment of cardiac metabolism, but in the past 8 years most of its indications have been in the ambit of assessment of patients with suspected malignancy, particularly those being considered for surgery59. The different applications relevant to lung cancer are listed in Table 11.3, but a discussion of the advantages of PET in the staging of lung cancer is given in Chapter 18. The use of [F-18]fluoro-2-deoxy-glucose (FDG)-PET in oncology is based on its ability to identify the differences between glucose metabolism in various tissues. Neoplastic cells have a much higher rate of glycolysis that non-neoplastic cells. [F 18]FDG, a glucose analogue in which the oxygen molecule in position 2 is replaced by the positron-emitting 18 F, undergoes the same uptake as glucose, but is metabolically trapped and accumulates in neoplastic cells after phosphorylation by hexokinase. To gain a quantitative measure of FDG uptake, attenuationcorrected images are required; this is because the intensity of the photon emission of a lesion is position dependent, and therefore the intensity seen on the nonattenuation corrected whole-body images does not truly reflect the actual FDG uptake. If the images are corrected for photo-attenuation by a ‘transmission’ study which estimates the attenuating characteristics of the patient, quantification of FDG metabolism becomes possible. The use of a transmission study allows the

Table 11.3 INDICATIONS FOR [F-18]FLUORO-2DEOXYGLUCOSE PET IN RESPIRATORY ONCOLOGY Common clinical indications Evaluation of nodules and masses

• TECHNIQUES IN THORACIC IMAGING

Standardized Uptake Value (SUV) to be reported.The SUV of a lesion is a semiquantitative index of glucose utilization that is obtained by normalizing the accumulation of FDG in the lesion to the injected dose and patient body weight60.The criterion for a positive result is either greater uptake in the lesion than in the background mediastinum or a SUV of > 2.561. The most important role of FDG–PET is in the clarification of the nature of an incidental nodule or mass identified on an ‘anatomical’ study62. Based on several prospective studies, FDG–PET has proven to be accurate in differentiating benign from malignant lesions as small as 1 cm with an overall sensitivity of 96% (range 83–100%) and specificity of 79% (range 52–100%). Potential pitfalls in sensitivity are due to the fact that a critical mass of metabolically active malignant cells is required for PET diagnosis; false-negative findings can occur in lesions < 1 cm63 and in lesions with low metabolic activity, e.g. carcinoid tumours64 and bronchioloalveolar cell carcinomas65. Errors in specificity are due to FDG uptake in inflammatory conditions, such as bacterial pneumonia66 and particularly granulomatous diseases such as sarcoidosis67, tuberculosis, or Wegener’s granulomatosis. A further emerging use of PET is in the staging of nodal metastases with studies consistently showing significantly greater accuracy of PET compared with CT for the detection or exclusion of mediastinal nodal disease68. The use of PET will undoubtedly increase as the technique becomes more available and a routine part of the investigative algorithm of patients with suspected lung cancer. Table 11.4 summarizes the indications for PET in the diagnosis and staging of patients with lung cancer. PET may well have a role in the evaluation of other intrathoracic malignancies, particularly in the assessment of response to chemotherapy that may occur before there is any discernible morphological change in the tumour on conventional imaging. Finally, a whole new field—applying PET to molecular biology using new radiopharmaceutical probes—is under investigation. These techniques may allow the evaluation of molecular-targeted lung cancer therapies or even gene therapy.

POSITRON EMISSION TOMOGRAPHY– COMPUTED TOMOGRAPHY PET/CT imaging was introduced in 1998.The concept of combined PET/CT imaging is to supplement metabolic information

Locoregional staging Extrathoracic staging Applications under investigation Radiotherapy planning Evaluation of response post radiotherapy Evaluation of response post (induction) chemotherapy Follow-up and diagnosis of recurrence Molecular applications Early assessment of chemotherapy Assessment of molecular targeted therapy

Table 11.4 INDICATIONS FOR PET IN THE STAGING OF LUNG CANCER All patients who are staged on CT as candidates for surgery: to identify involved intrathoracic lymph nodes and distant metastases Patients who are otherwise surgical candidates but have, on CT, limited (one to two stations) N2/N3 disease of uncertain pathological significance All patients who are candidates for radical radiotherapy To investigate solitary pulmonary nodules in cases in which biopsy is not possible or has failed, depending on nodule size

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from a whole-body PET study with more detailed anatomical information, thereby improving diagnostic accuracy.

Image acquisition Conventional PET employs transmission images for photon attenuation correction using an external radiation source and consequently, a conventional whole-body PET study covering six to eight bed positions requires about 1 h for completion. PET/CT imaging differs in that it utilizes whole-body CT data for attenuation correction. Depending on the number of CT detectors used, attenuation correction is achieved within seconds to slightly over 1 min and thus whole-body imaging times are reduced by 50%. The incremental value of PET/CT over PET alone for staging and restaging of cancer has not been fully established, but preliminary data suggest significant increments in diagnostic and staging accuracy of NSCLC69,70. The latter study demonstrated that tumour staging and nodal staging were significantly more accurate with integrated PET/CT than with PET alone. Moreover, PET/CT provided additional information in 41% of patients, including localization of lymph nodes (n = 9), precise identification of chest wall infiltration (n = 3), correct differentiation between tumour and inflammation (n = 7) and localization of distant metastases (n = 2)70. However, it is important to note that this study did not examine prospectively whether the ‘additional information’ led to significant changes in patient management. More clinical trials with greater patient numbers will be required to firmly establish possible advantages of PET/CT over PET or CT alone for each type of cancer.

REFERENCES 1. Rong X J, Shaw C C, Liu X et al 2000 Comparison of an amorphous silicon/cesium iodide flat-panel digital chest radiography system with screen/film and computed radiography systems—a contrast-detail phantom study. Med Phys 28: 2328–2335 2. Garmer M, Hennigs S P, Jager H J et al 2000 Digital radiography versus conventional radiography in chest imaging: diagnostic performance of a large-area silicon flat-panel detector in a clinical CT-controlled study. Am J Roentgenol 174: 75–80 3. Floyd C E J, Warp R J, Dobbins J T et al 2001 Imaging characteristics of an amorphous silicon flat-panel detector for digital chest radiography. Radiology 218: 683–688 4. Fink C, Hallscheidt P J, Noeldge G et al 2002 Clinical comparative study with a large-area amorphous silicon flat-panel detector: image quality and visibility of anatomic structures on chest radiography. Am J Roentgenol 178: 481–486 5. Bacher K, Smeets P, Bonnarens K et al 2003 Dose reduction in patients undergoing chest imaging: digital amorphous silicon flat-panel detector radiography versus conventional film-screen radiography and phosphorbased computed radiography. Am J Roentgenol 181: 923–929 6. American Thoracic Society 2001 Guidelines for the management of adults with community-acquired pneumonia. Am J Respir Crit Care Med 163: 1730–1754 7. Metersky M L 2005 Is the lateral decubitus radiograph necessary for the management of a parapneumonic pleural effusion? Chest 124: 1129–1132 8. Klingenbeck-Regn K, Schaller S, Flohr T et al 1999 Subsecond multislice computed tomography: basics and applications. Eur J Radiol 31: 110–124

9. Hu H, He H D, Foley W D, et al 2000 Four multidetector-row helical CT: image quality and volume coverage speed. Radiology 215: 55–62 10. McCollough C H, Zink F E 1999 Performance evaluation of a multi-slice CT system. Med Phys 26: 2223–2230 11. Pappas J N, Donnelly L F, Frush DP 2000 Reduced frequency of sedation of young children with multisection helical CT. Radiology 215: 897–899 12. Wormanns D, Kohl G, Klotz E et al 2004 Volumetric measurements of pulmonary nodules at multi-row detector CT: in vivo reproducibility. Eur Radiol 14: 86–92 13. Yi C A, Lee K S, Kim E A et al 2004 Solitary pulmonary nodules: dynamic enhanced multi-detector row CT study and comparison with vascular endothelial growth factor and microvessel density. Radiology 233: 191–199 14. Revel M P, Petrover D, Hernigou A et al 2005 Diagnosing pulmonary embolism with four-detector row helical CT: prospective evaluation of 216 outpatients and inpatients. Radiology 234: 265–273 15. International Electrotechnical Commission 2002 60601-2-44 Amendment 1. Medical Electrical Equipment, part 2-44: Particular requirements for the safety of x-ray equipment for computed tomography. International Electrotechnical Commission, Geneva 16. Flohr T G, Schaller S, Stierstorfer K et al 2005 Multi-detector row CT systems and image-reconstruction techniques. Radiology 235: 756–773 17. Kalra K K, Maher M M, Toth T L et al 2004 Strategies for CT radiation dose optimization. Radiology 230: 619–628 18. Jung K J, Lee K S, Kim S Y et al 2000 Low-dose, volumetric helical CT: image quality, radiation dose, and usefulness for evaluation of bronchiectasis. Invest Radiol 35: 557–563 19. Yi C A, Lee K S, Kim T S et al 2003 Multidetector CT of bronchiectasis: effect of radiation dose on image quality. Am J Roentgenol 181: 501–505 20. Itoh S, Ikeda M, Arahata S et al 2000 Lung cancer screening: minimum tube current required for helical CT. Radiology 215: 175–183 21. Schoepf U J, Becker C R, Obuchowski N A et al 2001 Multi-slice computed tomography as a screening tool for colon cancer, lung cancer and coronary artery disease. Eur Radiol 11: 1975–1985 22. Cody D D, Moxley D M, Krugh K T et al 2004 Strategies for formulating appropriate MDCT techniques when imaging the chest, abdomen, and pelvis in pediatric patients. Am J Roentgenol 182: 849–859 23. Mahesh M, Scatarige J C, Cooper J et al 2001 Dose and pitch relationship for a particular multislice CT scanner. Am J Roentgenol 177: 1273–1275 24. Greess H, Nomayr A, Wolf H et al 2002 Dose reduction in CT examination of children by an attenuation-based on-line modulation of tube current (CARE Dose). Eur Radiol 12: 1571–1576 25. Leung A N 1997 Spiral CT of the thorax in daily practice: optimization of technique. J Thorac Imag 12: 2–10 26. Remy-Jardin M, Remy J, Artaud D et al 1997 Peripheral pulmonary arteries: optimization of the spiral CT acquisition protocol. Radiology 204: 157–163 27. Kuzo R S, Goodman L R 1997 CT evaluation of pulmonary embolism: technique and interpretation. Am J Roentgenol 169: 959–965 28. Hartmann I J, Lo R T, Bakker J et al 2002 Optimal scan delay in spiral CT for the diagnosis of acute pulmonary embolism. J Comput Assist Tomogr 26: 21–25 29. Schoellnast H, Deutschmann H A, Fritz G A et al 2005 MDCT angiography of the pulmonary arteries: Influence of iodine flow concentration on vessel attenuation and visualization. Am J Roentgenol 184: 1935–1939 30. Swensen S J, Viggiano R W, Midthun D E et al 2000 Lung nodule enhancement at CT: multicenter study. Radiology 214: 73–80 31. Harris K M, Adams H, Lloyd D C F et al 1993 The effect on apparent size of simulated pulmonary nodules of using three standard CT window settings. Clin Radiol 47: 241–244 32. Kelly D M, Hasegawa I, Borders R et al 2004 High-resolution CT using MDCT: Comparison of degree of motion artefact between volumetric and axial methods. Am J Roentgenol 182: 757–759 33. Murata K, Khan A, Rojas K A et al 1988 Optimization of computed tomography technique to demonstrate the fine structure of the lung. Invest Radiol 23: 170–175

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34. Volpe J, Storto M L, Lee K et al 1997 High-resolution CT of the lung: determination of the usefulness of CT scans obtained with the patient prone based on plain radiographic findings. Am J Roentgenol 169: 369–374 35. Aberle D R, Gamsu G, Ray C S 1988 High-resolution CT of benign asbestos-related diseases: Clinical and radiographic correlation. Am J Roentgenol 151: 883–891 36. Arakawa H, Webb W R, McCowin M et al 1998 Inhomogeneous lung attenuation at thin-section CT: diagnostic value of expiratory scans. Radiology 206: 89–94 37. Lucidarme O, Coche E, Cluzel P et al 1998 Expiratory CT scans for chronic airway disease: correlation with pulmonary function test results. Am J Roentgenol 170: 301–307 38. Lomas D J, Padley S P G, Flower C D R 1993 The sonographic appearances of pleural fluid. Br J Radiol 66: 619–624 39. Yang P C 1997 Ultrasound-guided transthoracic biopsy of peripheral lung, pleural, and chest-wall lesions. J Thorac Imag 12: 272–284 40. Suzuki N, Saitoh T, Kitamura S 1993 Tumour invasion of the chest wall in lung cancer: diagnosis with US. Radiology 187: 39–42 41. Fritscher-Ravens A, Soehendra N, Schirrow L et al 2000 Role of transesophageal endosonography-guided fine-needle aspiration in the diagnosis of lung cancer. Chest 117: 339–345 42. Bhutani M S, Hawes R H, Hoffman B J 1997 A comparison of the accuracy of echo features during endoscopic ultrasound (EUS) and EUSguided fine-needle aspiration for diagnosis of malignant lymph node invasion. Gastrointest Endosc 45: 474–479 43. Gress F G, Savides T J, Sandler A et al 1997 Endoscopic ultrasonography, fine-needle aspiration biopsy guided by endoscopic ultrasonography, and computed tomography in the preoperative staging of non-smallcell lung cancer: a comparison study. Ann Intern Med 127: 604–612 44. LeBlanc J, Devereaux B M, Imperiale T F et al 2005 Endoscopic ultrasound in non-small cell lung cancer and negative mediastinum on computed tomography. Am J Respir Crit Care Med 171: 177–182 45. Outwater E K, Siegelman E S, Hunt J L 2001 Ovarian teratomas: tumor types and imaging characteristics. RadioGraphics 21: 475–490 46. Semelka R C, Cem B N, Wilber K P et al 2000 Breath-hold 3D gradientecho MR imaging of the lung parenchyma: evaluation of reproducibility of image quality in normals and preliminary observations in patients with disease. J Magn Reson Imaging 11: 195–200 47. Biederer J, Both M, Graessner J et al 2003 Lung morphology: fast MR imaging assessment with a volumetric interpolated breath-hold technique: initial experience with patients. Radiology 226: 242–249 48. Vassallo P, Matei C, Heston W D et al 1994 AMI-227-enhanced MR lymphography: usefulness for differentiating reactive from tumorbearing lymph nodes. Radiology 193: 501–506 49. Pannu H K, Wang K P, Borman T L et al 2000 MR imaging of mediastinal lymph nodes: evaluation using a superparamagnetic contrast agent. J Magn Reson Imag 12: 899–904 50. Meaney J F M, Weg J G, Chenevert T L et al 1997 Diagnosis of pulmonary embolism with magnetic resonance angiography. N Engl J Med 336: 1422–1427 51. Gupta A, Frazer C K, Ferguson J M et al 1999 Acute pulmonary embolism: diagnosis with MR angiography. Radiology 210: 353–359 52. Amundsen T, Kvaerness J, Jones R A et al 1997 Pulmonary embolism: detection with MR perfusion imaging of lung—a feasibility study. Radiology 203: 181–185 53. Kauczor H U, Hofmann D, Kreitner K F et al 1996 Normal and abnormal pulmonary ventilation: visualization at hyperpolarized He-3 MR imaging. Radiology 201: 564–568 54. Eberle B, Markstaller K, Schreiber W G et al 2001 Hyperpolarised gases in magnetic resonance: a new tool for functional imaging of the lung. Swiss Med Wkly 131: 503–599 55. Hanisch G, Schreiber W, Diergarten T et al 2000 Investigation of intrapulmonary diffusion by 3He MRI. Eur Radiol 10 (suppl 1): S345

• TECHNIQUES IN THORACIC IMAGING

56. Kauczor H 2003 Hyperpolarized helium-3 gas magnetic resonance imaging of the lung. Top Magn Reson Imaging 14: 223–230 57. British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group. British Thoracic Society guidelines for the management of suspected acute pulmonary embolism. Thorax 58: 470–483 58. Reinartz P, Wildberger J E, Schaefer W et al 2004 Tomographic imaging in the diagnosis of pulmonary embolism: a comparison between V/Q lung scintigraphy in SPECT technique and multislice spiral CT. J Nucl Med 45: 1501–1508 59. Vansteenkiste J F 2002 Imaging in lung cancer: positron emission tomography scan. Eur Respir J 19 (suppl 35): 49s–60s 60. Meikle S R, Bailey D L, Hooper P K et al 1995 Simultaneous emission and transmission measurements for attenuation correction in wholebody PET. J Nucl Med 36: 1680–1688 61. Patz E F, Lowe V J, Hoffman J M et al 1993 Focal pulmonary abnormalities: evaluation with F-18 fluorodeoxyglucose PET scanning. Radiology 188: 487–490 62. Vansteenkiste J F, Stroobants S G, De Leyn P R et al 1997 Mediastinal lymph node staging with FDG-PET scan in patients with potentially operable non-small cell lung cancer: a prospective analysis of 50 cases. Leuven Lung Cancer Group. Chest 112: 1480–1486 63. Dewan N A, Gupta N C, Redepenning L S et al 1993 Diagnositc efficacy of PET-FDG imaging in solitary pulmonary nodules. Potential role in evaluation and management. Chest 104: 997–1002 64. Erasmus J J, McAdams H P, Patz E F Jr et al 1998 Evaluation of primary pulmonary carcinoid tumors using FDG PET. Am J Roentgenol 170: 1369–1373 65. Kim B T, Kim Y, Lee K S et al 1998 Localized form of bronchioloalveolar carcinoma. FDG PET findings. Am J Roentgenol 170: 935–939 66. Kapucu L O, Meltzer C C, Townsend D W et al 1998 Fluorine-18fluorodeoxyglucose uptake in pneumonia. J Nucl Med 39: 1267–1269 67. Brudin L H, Valind S O, Rhodes C G et al 1994 Fluorine-18 deoxyglucose uptake in sarcoidosis measured with positron emission tomography. Eur J Nucl Med 21: 297–305 68. Steinert H C, Hauser M, Allemann F et al 1997 Non-small cell lung cancer: nodal staging with FDG PET versus CT with correlative lymph node mapping and sampling. Radiology 202: 441–446 69. Cerfolio R J, Ojha B, Bryant A S et al 2004 The accuracy of integrated PET-CT compared with dedicated PET alone for the staging of patients with nonsmall cell lung cancer. Ann Thorac Surg 78: 1017–1023 70. Lardinois D, Weder W, Hany T F et al 2003 Staging of non-smallcell lung cancer with integrated positron-emission tomography and computed tomography. N Engl J Med 348: 2500–2507

SUGGESTED FURTHER READING Flohr T G, Schaller S, Stierstorfer K et al 2005 Multi-detector row CT systems and image-reconstruction techniques. Radiology 235: 756–773 Kalra M K, Maher M M, Toth T L et al 2004 Strategies for CT radiation dose optimization. Radiology 230: 619–628 Kauczor H U, Chen X J, Beek E R J et al 2001 Pulmonary ventilation imaged by magnetic resonance: at the doorstep of clinical application. Eur Respir J 17: 1008–1023 Müller N L 2002 Computed tomography and magnetic resonance imaging: past, present and future. Eur Respir J 19 (suppl 35): 3s–12s Remy-Jardin M, Remy J, Mayo J R et al 2001 CT angiography of the chest. Lippincott, Williams and Wilkins, Philadelphia Schoepf U J (ed) 2004 Multidetector-row CT of the thorax. Springer Verlag, Berlin Schrevens L, Lorent N, Dooms C et al 2004 The role of PET scan in diagnosis, staging and management of non-small cell lung cancer. Oncologist 9: 633–643

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The Normal Chest

12

Simon Padley and Sharyn L. S. MacDonald

• • • • • •

The lungs The central airways The lungs beyond the hila The hila The mediastinum The diaphragm

THE LUNGS Each lung is divided into lobes surrounded by pleura. There are two lobes on the left: the upper and lower, separated by the major (oblique) fissure; and three on the right: the upper, middle and lower lobes separated by the major (oblique) and minor (horizontal) fissures. The fissures are frequently incomplete, particularly medially, containing localized defects which form an alveolar pathway for collateral air drift and the spread of disease. For a fissure to be visualized on conventional radiographs, the X-ray beam has to be tangential to the fissure. In most people, some or all of the minor fissure is seen in the frontal projection, but neither major fissure can be identified. In the lateral view, both the major and minor fissures are often identified, but usually only part of any fissure is seen; in fact, it is very unusual to see both left and right major fissures in their entirety. The major fissures have similar anatomy on the two sides. They run obliquely anteriorly and inferiorly from approximately the fifth thoracic vertebra to pass through the hilum and contact the diaphragm 0–3 cm behind the anterior costophrenic angle. Each major fissure follows a gently curving plane somewhat similar to a propeller blade (Fig. 12.1), with the upper portion facing anteriorly and laterally, and the lower portion facing forward and medially. Owing to the undulating course of the major fissure, either fissure may be seen as two lines on the lateral view. Consequently it may appear to the unwary that a fissure is displaced when it is in fact in its normal position, or both fissures may appear to be in their normal positions when in reality one of them is so displaced that it is no longer visible.

The inferior few centimetres of either or both major fissures may be widened owing to the presence of fat or pleural thickening between the leaves of the pleura. In these circumstances the contact with the diaphragm will often be broadened and lead to a localized loss of silhouette, an appearance referred to as the juxtaphrenic peak. With modern multislice computed tomography (CT), the normal major fissures are frequently visible, but if not clearly defined the position can be inferred from the presence of a relatively avascular zone that forms the outer cortex of the lobe. With high-resolution CT (HRCT), a normal major fissure is seen as a thin line traversing the avascular zone1, although it may be represented as two parallel lines on at least one level in approximately one-third of the population because of an artefact related to cardiac and respiratory motion2. The minor fissure fans out anteriorly and laterally from the right hilum in a horizontal direction to reach the chest wall. On a standard chest radiograph, the minor fissure contacts the chest wall at the axillary portion of the right sixth rib. The fissure curves gently, with its anterior and lateral portion usually curving downwards. Because of the curvature of the major fissure described above, part of the minor fissure may be projected posterior to the right major fissure on the lateral view. On CT the minor fissure position is represented by an oval area of reduced vascularity at the level of the bronchus intermedius (Fig. 12.2). The normal minor fissure is not seen as a line on axial CT imaging but is apparent on multiplanar reformats. In 1% of the population an accessory fissure3 called the ‘azygos lobe fissure’ (Fig. 12.3) is seen. This fissure contains the azygos vein at its lower end and results from failure of normal migration of the azygos vein from the chest wall to its usual position in the tracheobronchial angle and persistence of the invaginated visceral and parietal pleurae.There is no corresponding alteration in the segmental architecture of the lung, so the term ‘lobe’ is a misnomer. The ‘azygos lobe’ may, however, be smaller and therefore less transradiant than corresponding normal lung4. On CT the altered course of the azygos vein can be seen traversing the lung (Fig.12.3B).

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Figure 12.1 The different position and shape of the major fissures (arrows) in the lower and the upper zones is well shown by CT. Note that (A) below the hila, the major fissures bow forward, whereas (B) above the hila, the major fissures bow backward. (The images are high-resolution thin-section [1.5 mm] CT scans.) Sagittal reformats from the (C) right and (D) left lungs demonstrate the detail of fissure anatomy available on this 16-channel CT study.

Figure 12.2 Minor fissure on CT. (A) The minor fissure is apparent as an area of avascularity anterior to the major fissure. In this example the slightly bowed horizontal fissure undulates through the plane of the slice. (B) The position of the minor fissure, in another patient, is indicated by the oval deficiency of vessels in the right mid zone (arrows).

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Figure 12.3 (A) Azygos lobe fissure (curved arrows) and aortic nipple (horizontal straight arrow). The azygos vein in the lower end of the fissure is well seen (lower curved arrow). Note its absence from its usual location in the right tracheobronchial angle (open arrow). The aortic nipple, due to the left superior intercostal vein, is particularly large in this example. (B) CT of the azygos lobe fissure.

Other accessory fissures are occasionally identified3. A minor fissure may separate the lingular segments from the remainder of the upper lobe, similar to the right minor fissure. A horizontally orientated fissure, a superior accessory fissure, may separate the apical segment from the basal segments of either lower lobe. An inferior accessory fissure is sometimes seen in one or other lower lobe, usually the right, separating the medial and anterior basal segments. This fissure runs obliquely upward and medially towards the hilum from the diaphragm. The inferior pulmonary ligaments5 are pleural reflections from the mediastinum which hang down from the hila and are analogous in shape to the peritoneal reflections forming the broad ligament of the uterus. These two layers of pleura may extend down to the diaphragm or may have a free inferior edge. The intersegmental septum of the lower lobe, a septum within the lung immediately beneath the inferior pulmonary ligament, is often visible on CT (Fig. 12.4)6.When the inferior pulmonary ligament reaches the diaphragm it may contain a small amount of fat. This may efface the diaphragm, resulting in a juxtaphrenic peak. Otherwise neither the intersegmental septum nor the inferior pulmonary ligament is visible on plain radiographs.

THE CENTRAL AIRWAYS The trachea is a straight tube that, in children and young adults, passes inferiorly and posteriorly in the midline. In subjects

Figure 12.4 Intersegmental septum deep to the inferior pulmonary ligament shown by CT (arrows).

with unfolding and ectasia of the aorta the trachea may deviate to the right and may also bow forward. In cross-section the trachea is usually round, oval, or oval with a flattened posterior margin. Maximum coronal and sagittal diameters in adults on plain chest radiography are 21 and 23 mm, respectively, for women, and 25 and 27 mm for men7. On CT, which allows precise assessment of diameters and cross-sectional areas without magnification, the mean transverse diameter is 15.2 mm (sd 1.4) for women and 18.2 mm (sd 1.2) for men,

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the lower limit of normal being 12.3 mm for women, and 15.9 mm for men8. The diameters in growing children and young adults have been documented9. Calcification of the cartilage rings of the trachea is a common normal finding after the age of 40 years, increasing in frequency with age. The trachea divides into the two mainstem bronchi at the carina. In children the angles are symmetrical, but in adults the right mainstem bronchus has a steeper angle than the left. The range of angles is wide, and alterations in angle can be diagnosed only by right–left comparisons, not by absolute measurement. The left main bronchus extends up to twice as far as the right main bronchus before giving off its upper lobe division. The lobar and segmental branching pattern is shown in Figure 12.5. There are many variations of the segmental and subsegmental branches10,11. Airways to subsegmental level can be routinely identified on volumetric thin-collimation CT.

THE LUNGS BEYOND THE HILA The usual method of deciding normal lung density in the frontal view is by comparison with equivalent areas on the opposite side. Since this is not possible on the lateral chest radiograph, the detection of subtle densities is more difficult, but the density over the spine should decrease gradually as the eye travels down the spine until the diaphragm is reached. Certain other comparisons can be made, but are less reliable: the density of the high retrosternal areas is approximately equal to that of the area immediately posterior to the left ventricle; the density over the heart is usually similar to that over the shoulders; and, apart from the cardiac fat pads and overlying ribs, there should be no abrupt change in density over the heart shadow. The segmental bronchi divide into smaller and smaller divisions until after 6–20 divisions they become bronchioles and

Figure 12.5 Diagram illustrating the anatomy of the main bronchi and segmental divisions. The nomenclature is that approved by the Thoracic Society. (Courtesy of the Editors of Thorax.)

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no longer contain cartilage in their walls. The bronchioles divide and the last of the purely conducting airways are known as the terminal bronchioles, beyond which lie the alveoli. The walls of the segmental bronchi are invisible on the chest radiograph unless seen end-on, when they may cause ring shadows (Fig.12.6). The acinus, which is 5–6 mm in diameter, comprises respiratory bronchioles, alveolar ducts and alveoli. The acini are grouped together in lobules of three to five acini which, in the lung periphery, are separated by septa and together comprise

the secondary pulmonary lobule.These peripheral interlobular septa, when thickened by disease, are the so-called septal or Kerley B lines. The bronchopulmonary segments are based on the divisions of the bronchi.The boundaries between segments are complex in shape and have been likened to the pieces of a three-dimensional (3D) jigsaw puzzle; there is no septation between them (except in the rare instance of a patient with accessory fissures). Atelectasis or pneumonia may predominate in one or other segment, but rarely conforms precisely to the whole of just one segment, since collateral air drift occurs across the segmental boundary. The position of the segments as seen on standard radiographs is illustrated in Figure 12.7. The pulmonary blood vessels (Fig. 12.8) are responsible for branching linear markings within the lungs both on conventional radiographs and CT. It is not possible to distinguish arteries from veins in the outer two-thirds of the lungs on plain radiographs. Centrally, the orientations of the arteries and veins differ: the lower lobe veins run more horizontally and the lower lobe arteries more vertically. In the upper lobes, the arteries and veins show a similar gently curving vertical orientation, but the upper lobe veins (when not superimposed on the arteries) lie lateral to the arteries and can sometimes be traced to the main venous trunk, the superior pulmonary vein. The diameter of the blood vessels beyond the hilum varies with the position of the patient and with various haemodynamic factors. On plain chest radiographs taken in the upright position, there is a gradual increase in the relative diameter of vessels equivalent in distance from the hilum as the eye travels from apex to base.The differences are abolished when the patient lies supine. These observations correlate

Figure 12.6 Ring shadows (arrows) due to end-on bronchi as a normal finding on chest radiography. The patient has a dual chamber pacing system.

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6 10

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• THE NORMAL CHEST

16

Figure 12.7 Diagrams of position of segments seen on plain frontal and lateral chest radiographs. There is substantial overlap of the projected images of the segments in both views; this overlap is worse in the frontal than the lateral projection. (A) Shows only the segments in the upper lobes and the middle lobe; (B) shows only the segments in the lower lobes; (C,D) show all the segments in the right and left lung, respectively, in the lateral view. H = hila, 1 = apical segment of right upper lobe (RUL), 2 = posterior segment of RUL, 3 = anterior segment of RUL, 4 = lateral segment of right middle lobe (RML), 5 = medial segment of RML, 6 = apical posterior segment of left upper lobe (LUL), 7 = anterior segment of LUL, 8 = superior segment of lingula, 9 = inferior segment of lingula, 10 = apical (superior) segment of right lower lobe (RLL), 11 = medial basal segment of RLL, 12 = anterior basal segment of RLL, 13 = lateral basal segment of RLL, 14 = posterior basal segment of RLL, 15 = apical (superior) segment of left lower lobe (LLL), 16 = anterior basal segment of LLL, 17 = lateral basal segment of LLL, 18 = posterior basal segment of LLL.

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Figure 12.8 Pulmonary angiogram shows appearances in (A) arterial phase and (B) venous phase. Note the difference in arrangement of the central arteries and veins. The peripheral arteries show similar anatomy to the peripheral veins. (C) Coronal maximum intensity projection slab image from a CT pulmonary angiogram demonstrating the combined arterial and venous phase image in a patient with normal circulation.

with physiological studies of perfusion which show that in the erect position there is a gradation of blood flow (the lower zones showing greater blood flow than the upper zones) from apex to base, a difference that is less obvious in the supine patient. While a general statement regarding these differences in zonal blood vessel size can be made, it is difficult to draw conclusions from the size of any particular peripheral pulmonary vessel. Certain measurements have, however, been suggested for upright chest radiographs: 1 The artery and bronchus of the anterior segment of either or both upper lobes are frequently seen end-on.The diameter of the artery is usually much the same as the diameter of the bronchus (4–5 mm). In the authors’ experience, an endon vessel with a diameter of over 1.5 times the diameter of the adjacent bronchus indicates that the vessel is increased in size. 2 Vessels in the first anterior interspace should not exceed 3 mm in diameter. A rich network of lymphatic vessels drains the lung and pleura to the hilar lymph nodes. The sub-pleural lymphatics are found beneath the pleura at the junction of the interlobular septa with the pleura. These vessels connect with each other and with the lymphatic vessels accompanying the veins in the interlobular septa. Lymph then flows to the hilum via deep lymphatic channels that run peribronchially and in the deep septa of the lungs. Under normal circumstances the lymphatic network is invisible radiographically but when thickened the septa are seen as line shadows known as septal or Kerley lines. Thickened interlobular septa correspond to Kerley B lines and thickened deep septa correspond to Kerley A lines. There are a few intrapulmonary lymph nodes, but they are small and cannot be identified on a chest radiograph but may be seen as small, peripherally located ellipsoid nodules on CT12,13.

THE HILA Understanding the normal hilum on plain radiography, CT and magnetic resonance imaging (MRI) requires an appreciation of the anatomy of the major blood vessels (Figs 12.9–12.13). On plain radiograph and CT the densities of the normal hilum are due mainly to blood vessels (Figs 12.10–12.12). Normal lymph nodes cannot be recognized as discrete structures, and the bronchial walls contribute little to the bulk of the hila, being thin and easily recognized for what they are. On MRI (Fig. 12.13), the lack of signal from fast-flowing blood within the vessels or from air in the bronchi means that there is relatively little signal generated from normal hilar structures on standard spin-echo sequences. The only signal will be from slow-flowing blood in the vessels, from the bronchial walls, and from the fat and hilar nodes. Normal lymph nodes of just a few millimeters in size are often evident as discrete structures on submillimeter collimation multislice CT. The major points to remember when viewing the hila are: 1 The transverse diameter of the lower lobe arteries before their segmental divisions can be determined with reasonable accuracy: they measure 9–16 mm on the normal postero-anterior (PA) chest radiograph (Fig. 12.11). 2 The posterior walls of the right main bronchus and its division into the right upper lobe bronchus and bronchus intermedius are outlined by air and appear as a thin stripe on lateral plain radiographs (Fig. 12.14) and on CT (Fig. 12.12).The posterior walls of the equivalent bronchi on the left are rarely visible on the plain radiograph because the left lower lobe artery intervenes between the lung and the bronchial tree. The lung does, in fact, frequently invaginate between the left lower lobe artery and the descending aorta to contact the posterior wall of the left lower lobe bronchus, but this is usually only visible on CT or MRI. 3 The right pulmonary artery passes anterior to the major bronchi, whereas the left pulmonary artery arches superior to the left main bronchus. The central portion of the right

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• THE NORMAL CHEST

Figure 12.9 Diagrams of the relationships between the hilar blood vessels and bronchi. (A) Frontal view. (B) Right posterior oblique view of right hilum. (C) Left posterior oblique view of left hilum. (D) Lateral chest radiograph with major blood vessels drawn in. IPV = inferior pulmonary vein—only one has been drawn in since they are superimposed, LPA = left pulmonary artery, LSPV = left superior pulmonary vein, RPA = right pulmonary artery; RSPV = right superior pulmonary vein. (Diagrams drawn by Ron Ervin and reproduced with permission from Armstrong P (ed) 1983 Critical problems in diagnostic radiology. Lippincott, Philadelphia.)

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Figure 12.10 Normal digital PA chest radiograph demonstrating position and density of the hilar structures. Arrows indicate the hilar points, where the superior pulmonary vein crosses the descending lower lobe artery, the left normally being level with or slightly higher than the right.

Figure 12.11 Frontal view of hila in plain chest radiograph. The measurement points for the diameter of the right lower lobe artery are indicated.

Figure 12.12 CT of normal hila. Two-millimetre collimation images have been obtained through the hilar structures during contrast medium enhancement and displayed on lung windows (L-500, W 1500). (A) Section just below the tracheal carina at the origin of the right upper lobe bronchus, immediately posterior to the upper lobe vein (v). (B) Section through level of right main pulmonary artery (RPA) and bronchus intermedius (curved arrow). Note the tongue of lung that contacts the left main bronchus between the aorta (A) and the left lower lobe artery (straight arrow). Note also that the right lung contacts the posterior wall of the bronchus intermedius as it extends into the azygo-oesophageal recess. (C) Section through the level of the middle lobe bronchus (long arrow) at the point of origin of the bronchus to the superior segment of the right lower lobe (arrow). Note that the middle lobe bronchus separates the right lower lobe artery from the right superior pulmonary vein as it enters the left atrium (LA). The lung contacts the posterior wall of the right lower lobe bronchus as it extends into the azygo-oesophageal recess. (D) Section through the level of the inferior pulmonary veins (arrows). At this level the lower lobe arteries have bilaterally divided into basal segmental divisions and are therefore narrower than 1 cm in diameter.

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5 The pulmonary veins are similar on the two sides.The superior pulmonary vein is the anterior structure in the upper and mid hilum on both sides. Since, however, the central portions of the pulmonary arteries are so differently organized on the two sides, the relationships of the major veins to the arteries differ. On the right the superior pulmonary vein is separated from the central bronchi by the lower division of the right pulmonary artery, whereas on the left the superior pulmonary vein is separated from the pulmonary artery by the bronchial tree.

Figure 12.13 MRI of normal hilum. Note that there is relatively little signal from the hila because there is no signal either from air in the bronchial tree or from fast-flowing blood in the pulmonary artery or vein branches.

Both inferior pulmonary veins travel obliquely anteriorly and superiorly, inferior to the branches of the left lower lobe artery, to enter the left atrium. They are slightly posterior to the plane of the left lower lobe bronchi. They may be seen either end-on or in oblique cross-section in PA, lateral and oblique projections and may, therefore, simulate a mass.

THE MEDIASTINUM The radiographic anatomy of the mediastinum can be described from many points of view, depending on the technique that is under discussion. In this chapter only plain radiographs, CT and MRI will be considered in any detail, CT and MRI being illustrated first because an appreciation of the cross-sectional anatomy of the mediastinum helps in understanding the appearances on plain chest radiographs. The mediastinum is conventionally divided into superior, anterior, middle and posterior compartments. The exact anatomical boundaries of these divisions are unimportant to the radiologist (indeed they vary according to different authors), since they do not provide a clear-cut guide to disease and nor do their boundaries form any barriers to the spread of the disease.

Computed tomography and magnetic resonance imaging

Figure 12.14 Lateral view of the hila showing normal thickness of the posterior wall of the bronchus intermedius (arrow).

hilum consists of a combination of the right pulmonary artery and the superior pulmonary vein. Since these two vessels are immediately adjacent to one another (on the left, the left main bronchus lies between them), they may be responsible for a density that is sufficiently great to be confused with a mass on lateral plain radiographs and even, on occasion, on CT. 4 On lateral chest radiographs the angles between the middle and right lower lobe bronchi on the right, and the upper and lower lobe bronchi on the left, do not contain any large end-on vessels; a rounded shadow of greater than 1 cm in these angles is therefore unlikely to be a normal vessel14.

The blood vessels, trachea and main bronchi make up the bulk of the mediastinum, and the CT/MRI anatomy of these structures is illustrated in Figures 12.12–12.16. The thymus is situated anterior to the aorta and right ventricular outflow tract or pulmonary artery; it is often best appreciated on a section through the aortic arch or great vessels (Fig. 12.17). Before puberty15 the thymus fills in most of the mediastinum in front of the great vessels. During this period of life the gland varies so greatly in size that measurement is of little value in deciding normality. Approximate symmetry is the rule. Also, the thymus fills in the spaces between the great vessels and the anterior chest wall as if moulded by these structures. In adults the thymus is bilobed or triangular in shape. The maximum width and thickness of each lobe decreases with advancing age. Between the ages of 20 and 50, the average thickness as measured by CT decreases from 8–9 mm to 5–6 mm, the maximum thickness of each lobe being up to 15 mm. These diameters are greater on MRI, presumably because MRI demonstrates the thymic tissue even when it is partially replaced by fat. On MRI, sagittal images demonstrate the gland to be 5–7 cm long in its craniocaudad dimension.

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Figure 12.15 CT of normal mediastinum. (A–E) Five 1-cm thick sections have been selected to show the important anatomical features. The level of each section is illustrated in the diagram. A. Ao = ascending aorta, Ao arch = aortic arch, AV = azygos vein, D. Ao = descending aorta, IA = innominate artery, LA = left atrium, LCA = left carotid artery, LIV = left innominate vein, LPA = left pulmonary artery, LSA = left subclavian artery, MPA = main pulmonary artery, N = normal lymph node, OES = oesophagus, RA = right atrium, RIV = right innominate vein, RPA = right pulmonary artery, RVO = right ventricular outflow tract, SPV = superior pulmonary vein, SVC = superior vena cava, T = trachea.

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Figure 12.16 MRI of normal mediastinum and hila. Four sections have been chosen to show the important anatomical features: (A) is just below the tracheal carina; (B) is 1 cm below A; (C) is at the level of the right main pulmonary artery; (D) is at the level of the mid left atrium. A.Ao = ascending aorta, AV = azygos vein, BI = bronchus intermedius, D.Ao = descending aorta, LA = left atrium, LMBr = left main bronchus, LPA = left pulmonary artery; LV = left ventricle, MPA = main pulmonary artery, Oes = oesophagus, RA = right atrium, RMBr = right main bronchus, RSPV = right superior pulmonary vein, SPR = superior pericardial recess, SVC = superior vena cava, Th = thymus.

Figure 12.17 CT of normal thymus (arrows) in a young adult man.

In younger patients, the CT density of the thymus is homogeneous and close to that of other soft tissues, but after puberty the density gradually decreases owing to fatty replacement, so that above 40 years of age the thymus usually has an attenuation value identical to that of fat and is often indistinguishable from the adjacent mediastinal fat, apart from some residual thymic parenchyma which may be visible as streaky or nodular densities within the fat (Fig. 12.18)16,17. On MRI the intensity of the thymus in T1weighted images is similar to that of muscle and appreciably lower than that of mediastinal fat, although, as would be expected, this difference decreases with age. On T2weighted images, the intensity differences are slight and do not vary with age.

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Figure 12.18 Thymic residues (arrows) shown by CT.

Figure 12.19 Diagram showing AJCC–UICC classification of regional lymph nodes.

Lymph nodes are widely distributed in the mediastinum. Ninety-five per cent of normal mediastinal lymph nodes are less than 10 mm in diameter, and the remainder, with few exceptions, are less than 15 mm in diameter18–22. Lymph nodes in the paraspinal areas, in the region of the brachiocephalic veins and in the space behind the diaphragmatic crura are generally smaller, 6 mm or less, whereas nodes in the aortopulmonary window, pretracheal and lower paratracheal spaces, and subcarinal compartment are often 6–10 mm in diameter. Lymph nodes encircle the trachea and main bronchi except where the aorta, pulmonary artery, or oesophagus are in direct contact with the airway.There is no clear division between the various nodes, but they can be categorized according to site.

The nomenclature of mediastinal lymph nodes should accord with the terms agreed by the American Joint Committee on Cancer and the Union International Contre le Cancer (AJCC– UICC) designed for staging carcinoma of the bronchus (Fig. 12.19; Table 12.1)23,24. These terms replaced the previous American Thoracic Society (ATS) classification. The AJCC–UICC classification is based on cross-sectional imaging in that it is directly referable to axial cross-sectional anatomy. The plane tangential to the upper margin of the aortic arch is an important dividing plane with nodes above this level being designated as: ‘highest mediastinal nodes’ (station 1 if they are above the upper rim of the left brachiocephalic vein); ‘right, left and posterior upper paratracheal’ (stations 2R,

Table 12.1 AJCC–UICC CLASSIFICATIONS OF REGIONAL LYMPH NODES 1. Highest mediastinal nodes lie above a horizontal line at the upper rim of the bracheocephalic (left innominate) vein 2. Upper paratracheal nodes lie above a horizontal line drawn tangential to the upper margin of the aortic arch and below the inferior boundary of No1 nodes 3. Prevascular and retrotracheal nodes may be designated 3A and 3P: midline nodes are considered to be ipsilateral 4. Lower paratracheal nodes lie to the right or left of the midline of the trachea between a horizontal line drawn tangential to the upper margin of the aortic arch and a line extending across the right or left main bronchus at the upper margin of the ipsilateral upper lobe bronchus. They are contained within the mediastinal pleural envelope. NB: The left lower paratracheal nodes lie medial to the ligamentum arteriosum 5. Subaortic (aortopulmonary window) nodes lie lateral to the ligamentum arteriosum or the aorta or left pulmonary artery and proximal to the first branch of the left pulmonary artery and lie within the mediastinal pleural envelope 6. Para-aortic nodes (ascending aorta or phrenic) lie anterior and lateral to the ascending aorta and the aortic arch or the innominate artery, beneath a line tangential to the upper margin of the aortic arch 7. Subcarinal nodes lie caudal to the carina of the trachea, but not associated with the lower lobe bronchi or arteries within the lung 8. Para-oesophageal nodes (below carina) lie adjacent to the right or left of the midline, excluding subcarinal nodes 9. Pulmonary ligament nodes lie within the pulmonary ligament, including those against the posterior wall and lower part of the inferior pulmonary vein 10. Hilar nodes lie distal to the mediastinal pleura reflection and the nodes adjacent to the bronchus intermedius on the right 11. Interlobar nodes lie between the lobar bronchi 12. Lobar nodes lie adjacent to the distal lobar bronchi 13. Segmental nodes lie adjacent to the segmental bronchi 14. Subsegmental nodes lie around the subsegmental bronchi NB. Station 1 through 9 nodes lie within the mediastinal pleural envelope, whereas station 10 through 14 nodes lie outside the mediastinal pleura within the visceral pleura.

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2L and 3P, respectively); and ‘prevascular’ if they lie anterior to the arteries to the head and neck (station 3A). The nodes below the plane tangential to the upper margin of the aortic arch include the following: right and left lower paratracheal (stations 4R and 4L); subaortic (aortopulmonary window) nodes (station 5); para-aortic nodes which lie anterior and lateral to the ascending aorta, the aortic arch, or the proximal brachiocephalic artery (station 6); and subcarinal nodes, which lie beneath the main bronchi within the mediastinal pleura (station 7). Low down in the mediastinum are the para-oesophageal (station 8) and pulmonary ligament nodes (station 9). Nodes are also present in the retrocrural areas and cardiophrenic angles. The nodes outside the mediastinal pleura are hilar (station 10), interlobar (station 11), lobar, segmental and subsegmental (stations 12–14); all these nodes are removed at pneumonectomy. The oesophagus is visible on all axial CT and MRI sections from the root of the neck down to the diaphragm. It may contain a small amount of air in approximately 80% of normal people. If there is sufficient mediastinal fat, the entire circumference of the oesophagus can be identified, and if air is present in the lumen, the uniform thickness of the wall can be appreciated. Without air, the collapsed oesophagus appears circular or oval in shape and measures approximately 1 cm in its narrowest diameter. On MRI the signal intensity on T1-weighted images is similar to muscle but on T2-weighted images the oesophagus often shows much higher signal intensity than muscle.

• THE NORMAL CHEST

Ant. junction line IA LCA Paratracheal stripe

SVC

LSA T

Posterior tracheal stripe

Oesophagus Post. junction line

Pleuro-oesophageal line

A

Anterior junction line

Paratracheal stripe

Ao Arch

SVC T

Post. tracheal stripe

B

Oesophagus

Pleuro-oesophageal line

Radiographic appearances Plain chest radiographs provide limited information regarding mediastinal anatomy, since only the interfaces between the lung and the mediastinum are visualized (Fig. 12.20).

Junction lines25,26 When there is only a small amount of fat anterior to the ascending aorta and its major branches, the two lungs may be separated anteriorly by little more than the four intervening layers of pleura. In such patients an anterior junction line is visible on frontal chest radiographs (Fig. 12.21).The line diverges and fades out superiorly and cannot be identified above the level of the clavicles. It descends for a variable distance, usually deviating to the left, but never extending lower than the point where the two lungs separate to envelop the right ventricular outflow tract. The lungs may also come close together behind the oesophagus, forming the posterior junction line (Fig. 12.21). This line, unlike the anterior junction line, separates to envelop the aortic arch. It may reform below the aortic arch where the two lungs occasionally abut behind the oesophagus. Superiorly, the posterior junction line extends to the level of the lung apices where it diverges and disappears, a level appreciably higher than the medial ends of the clavicles. The differences in the superior extent of the anterior and posterior junction lines are related to the sloping boundary between the root of the neck and the thorax.

Oesophagus Azygo-oesophageal line Right paraspinal line

C

Ao Azygos vein Left paraspinal line

Figure 12.20 Diagrams illustrating the mediastinal boundaries and junction lines. The visualization of the junction lines on a plain chest radiograph is variable, depending on how much fat is present in the mediastinum and on how closely the two lungs approximate to one another. (A) Section just above the level of the aortic arch; (B) section through the aortic arch; (C) section through the heart.

The major value of being able to identify the anterior and posterior junction lines is that a mass, or other space-occupying process, in the junctional areas can be excluded if these lines are visible. Since both junction lines are inconsistently seen, however, the lack of visualization of one or both is not a reliable sign of disease.

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Figure 12.22 Right tracheal stripe (straight arrows) and pleurooesophageal line (curved arrows) demonstrated on (A) plain radiograph and (B) unenhanced CT.

Figure 12.21 Anterior junction line (curved arrows) and the supraaortic posterior junction line (straight arrows). Note that the supraaortic posterior junction line goes well above the level of the clavicles and extends down to the top of the aortic arch but then stops, whereas the anterior junction line starts below the clavicles and continues well below the aortic arch.

Right mediastinum above the azygos vein The right superior mediastinal border is formed by the right brachiocephalic (innominate) vein and the superior vena cava. With aortic or brachiocephalic (innominate) artery ectasia or unfolding, either of these veins may be pushed laterally or the mediastinal border may be formed by the aorta or the right brachiocephalic artery. The right paratracheal region can be seen through the right brachiocephalic vein and superior vena cava because the lung contacts the right tracheal wall from the level of the clavicles down to the azygos vein, producing a visible stripe of uniform thickness known as the right paratracheal stripe (Fig.12.22), between the tracheal air column and the lung.This stripe, which should be no more than 5 mm wide, is visible in approximately two-thirds of normal people. It consists of the wall of the trachea and the adjacent mediastinal fat, but no focal bulges due to individual paratracheal lymph nodes can be seen. As with the junction lines, the diagnostic value of this stripe is that its presence excludes a spaceoccupying process in the area where the stripe is visible. The azygos vein is outlined by air in the lung at the lower end of the right paratracheal stripe. The diameter of the azygos vein in the tracheobronchial angle is variable: it may be considered normal when its diameter is 10 mm or less. The nodes immediately beneath the azygos vein are known as azygos nodes and are not recognizable on the normal chest radiograph. The lung posterior to the trachea contacts the right wall of the oesophagus so that a recognizable border may be seen in

the frontal projection. If the oesophagus at this level contains air, then the right wall of the oesophagus is seen as a stripe, the so-called oesophageal–pleural stripe27, curving superiorly and laterally behind the tracheal air column (Fig. 12.22). In summary, on a frontal radiograph three interfaces are potentially recognizable in the right mediastinum above the azygos vein: the superior vena cava border, the right wall of the trachea, and the right wall of the oesophagus.

Left mediastinum above the aortic arch The mediastinal shadow to the left of the trachea above the aortic arch is of low density and is caused by the left carotid and left subclavian arteries together with the left brachiocephalic (innominate) and jugular veins. The usual appearance on the frontal projection is a gently curving border formed by the left subclavian artery, which fades out where the artery enters the neck. A separate interface may occasionally be discernible for the left carotid artery or left brachiocephalic vein. The outer margin of the left tracheal wall is virtually never outlined, because the lung is separated from the trachea by the aorta and other vessels listed above.

Trachea and retrotracheal area in the lateral view The air column in the trachea can be seen throughout its length as it descends obliquely inferiorly and posteriorly. The course of the trachea on a normal lateral view is straight, or bowed anteriorly in patients with aortic unfolding, with no visible indentation from adjacent vessels. Small indentations into the air column of the trachea from tracheal cartilage rings may be apparent on the lateral view. The carina cannot be identified on the lateral view (though the right main bronchus is often mistaken for it). Its anterior wall is visible in a minority of patients, but the posterior wall is usually seen because lung often passes behind the trachea, thereby permitting visualization of the posterior tracheal (stripe) band28.The thickness of this stripe is 2–3 mm, provided it is formed solely by the tracheal wall and pleura (Fig. 12.23). If a large amount

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Figure 12.23 Lateral view of trachea and major bronchi. (A) In this example, the posterior wall of the trachea is outlined by lung posterior to it (arrow). (B) In this example, the collapsed oesophagus is between the lung and the trachea (arrow).

of air is present in the oesophagus, the posterior tracheal band may be much thicker, since it then comprises the combined thicknesses of the posterior tracheal wall and the anterior oesophageal wall. Alternatively, the lung may be separated from the trachea by the full width of a collapsed oesophagus, leading to a band of density measuring 10 mm or more (Fig. 12.23).

Supra-aortic mediastinum on the lateral view A variable proportion of the aortic arch and its major branches is visible on the lateral view, depending largely on the degree of aortic unfolding. The brachiocephalic (innominate) artery is the only branch vessel that is recognizable with any frequency. It arises anterior to the tracheal air column; usually the origin is unclear but, after a variable length, the posterior wall can be seen as a gently S-shaped interface as it crosses the tracheal air column. The left and right brachiocephalic (innominate) veins are also sometimes visible on the lateral view. The left brachiocephalic vein is seen as an extrapleural bulge behind the manubrium in a small proportion of normal people (Fig. 12.24).

Figure 12.24 Bulge behind manubrium representing normal left innominate (brachiocephalic) vein (arrow).

Right middle mediastinal border below the azygos arch Below the azygos arch, the right lower lobe makes contact with the right wall of the oesophagus and the azygos vein as it ascends next to the oesophagus. This portion of the lung is known as the azygo-oesophageal recess, and the interface is known as the azygo-oesophageal line (Fig. 12.25). The shape of the azygos arch varies considerably in different subjects and therefore the shape of the upper portion of the azygo-oesophageal line varies accordingly. The upper few centimetres of the azygo-oesophageal line are, however, always straight or concave toward the lung, so that a convex shape suggests the

presence of a subcarinal mass or left atrial enlargement. The azygo-oesophageal line can be traced down to the posterior costophrenic angle in normal subjects.

Left cardiac border below the aortic arch This left cardiac border is formed by the main pulmonary artery and heart. The pleura smoothing the angle between the mid-portion of the aortic arch and the main and left pulmonary artery, the so-called aortic–pulmonary mediastinal stripe29, is the lateral extent of the aortopulmonary

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Figure 12.25 Azygo-oesophageal line (arrows).

window. Because the aortopulmonary window is a sensitive place to look for lymph node enlargement, Blank and Castellino30 investigated the variable shape of this pleural reflection, as illustrated in Figure 12.26. A small ‘nipple’ may occasionally be seen projecting laterally from the aortic knuckle owing to the presence of the left superior intercostal vein31,32 (see Fig. 12.3A). The vein, which is formed by the junction of the left first to fourth intercostal veins, arches forward around the aorta just below the origin of the left subclavian artery to enter the left brachiocephalic vein. This normal nipple should not be misinterpreted as adenopathy projecting from the aortopulmonary window. The interface between the lung and the left wall of the aorta can almost invariably be followed down to the level of the diaphragm, though contact with the proximal portion of the left pulmonary artery may silhouette a small portion of the interface.The shape varies with the degree of aortic unfolding. Though the lung invaginates between the heart and aorta to contact the left wall of the oesophagus, the interface with the oesophagus may be seen as a line if air is present within the lumen of the oesophagus.

Paraspinal lines Although lymph nodes and intercostal veins occupy the space between the spine and the lung, they cannot normally be recognized individually. In individuals with little fat, the interfaces, known as the paraspinal lines, may closely reflect the

Figure 12.26 Patterns of pleural reflection along the left border of the great vessels and heart. The heavy line indicates the visible pleural interface. (Adapted from Blank N, Castellino R A 1972 Patterns of pleural reflections of the left superior mediastinum: normal anatomy and distortions produced by adenopathy. Radiology 102: 585–589, with permission from the Radiological Society of North America).

undulations of the lateral spinal ligaments, but the more fat there is, the more these undulations are smoothed out. The thickness of the left paravertebral space is usually greater than that of the right and can be more than 10 mm in obese subjects. Aortic unfolding contributes to the thickness of the left paraspinal line; as the aorta moves posteriorly and laterally, it strips the pleura from its otherwise close contact with the profiled portions of the spine.

Retrosternal line The band-like opacity simulating pleural or extrapleural disease is often seen along the lower third of the anterior chest wall on a lateral chest radiograph (Fig. 12.27)33. This density is due to mediastinal fat and to the differing anterior extent of the left and right lungs. The left lung does not contact the most anterior portion of the left thoracic cavity at these levels because the heart occupies the space. The band-like opacity is therefore accounted for by the normal heart and mediastinum, rather than by disease.

THE DIAPHRAGM The diaphragm consists of a large dome-shaped central tendon surrounded by a sheet of striated muscle which is attached to ribs 7 to 12 and to the xiphisternum. The two diaphragmatic crura, which arise from the upper three lumbar vertebrae, arch superiorly and anteriorly to form the margins of the aortic

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Figure 12.28 Right phrenic nerve as it passes over the surface of the right hemidiaphragm (arrows).

Figure 12.27 Retrosternal stripe (arrowheads) and inferior vena cava in lateral projection (arrow).

and oesophageal hiatuses. The median arcuate ligament connecting the two crura forms the anterior margin of the aortic hiatus, and the crura themselves form its lateral boundary. The oesophageal hiatus lies anterior to the aortic hiatus, and anterior to that lies the hiatus for the inferior vena cava, which is situated within the central tendon immediately beneath the right atrium. In most individuals, the diaphragm has a smooth domed shape, but a scalloped outline is also common. The angle of contact with the chest wall is acute and sharp, but blunting of this angle can be normal in athletes, because they can depress their diaphragm to a remarkable degree on deep inspiration. The normal right hemidiaphragm is found at about the level of the anterior portion of the sixth rib, with a range of approximately one interspace above or below this level34. In most people, the right hemidiaphragm is 1.5–2.5 cm higher than the left, but the two hemidiaphragms are at the same level in some 9% of the population. In a few normal individuals the left hemidiaphragm is up to 1 cm higher than the right. The normal excursion of the diaphragm is usually between 1.5 and 2.5 cm, though greater degrees of movement are not uncommon. Transabdominal ultrasound, which is capable of providing accurate real-time measurement of movement, shows a considerable normal range of between 2.0 and 8.6 cm, the mean excursion of the right hemidiaphragm on deep inspiration being 53 mm (sd 16.4) and that of the left being 46 mm (sd 12.4)35. Incomplete muscularization, known as eventration, is also common. An eventration is composed of a thin membranous sheet replacing what should be muscle. Usually it is partial, involving one-half to one-third of the hemidiaphragm. The lack of muscle manifests itself radiographically as elevation of the affected portion of the diaphragm, and the usual appear-

ance is one of a smooth hump on the contour of the diaphragm.Total eventration of a hemidiaphragm, which is much more common on the left than the right, results in elevation of the whole hemidiaphragm; on fluoroscopy hemidiaphragm movement is poor, absent, or paradoxical, and severe cases of congenital eventration cannot be distinguished from acquired paralysis of the phrenic nerve. A linear density arising from the lateral wall of the inferior vena cava (Fig. 12.28) is often seen coursing over the surface of the right hemidiaphragm.This line represents pleura and an envelope of fat investing the phrenic nerve, according to Berkman et al36, or the inferior phrenic artery and vein, according to Ujita et al37.

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10. Jardin M, Remy J 1986 Segmental bronchovascular anatomy of the lower lobes: CT analysis. Am J Roentgenol 147: 457–468 11. Lee K S, Bae W K, Lee B H et al 1991 Bronchovascular anatomy of the upper lobes: evaluation with thin section CT. Radiology 181: 765–772 12. Oshiro Y, Kusumoto M, Moriyama N et al 2002 Intrapulmonary lymph nodes: thin-section CT features of 19 nodules. J Comput Assist Tomogr 26: 553–557 13. Hyodo T, Kanazawa S, Dendo S et al 2004 Intrapulmonary lymph nodes: thin-section CT findings, pathological findings, and CT differential diagnosis from pulmonary metastatic nodules. Acta Med Okayama 58: 235–240 14. Park C-K, Webb W R, Klein J S 1991 Inferior hilar window. Radiology 178: 163–168 15. Mendelson D S 2001 Imaging of the thymus. Chest Surg Clin North Am 11: 269–293 16. Dixon A K, Hilton C J, Williams C T 1981 Computed tomography and histological correlation of the thymic remnant. Clin Radiol 32: 255–257 17. Moore A V, Korobkin M, Olanow W et al 1983 Age-related changes in the thymus gland: CT-pathologic correlation. Am J Roentgenol 141: 241–246 18. Genereux G P, Howie J L 1984 Normal mediastinal lymph node size and number: CT and anatomic study. Am J Roentgenol 142: 1095–1100 19. Glazer G M, Gross B H, Quint L E et al 1985 Normal mediastinal lymph nodes: number and size according to American Thoracic Society mapping. Am J Roentgenol 144: 261–265 20. Schynder P A, Gamsu G 1982 CT of the pretracheal retrocaval space. Am J Roentgenol 136: 303–308 21. Ingram C E, Belli A M, Lewards M D et al 1989 Normal lymph node size in the mediastinum: a retrospective study in two patient groups. Clin Radiol 40: 355–339 22. Murray J G, O’Driscoll M, Curtin J J 1995 Mediastinal lymph node size in an Asian population. Br J Radiol 68: 348–350 23. Mountain C F, Dresler C M 1997 Regional lymph node classification for lung cancer staging. Chest 111: 1718–1723

24. Cymbalista M, Waysberg A, Zacharias C et al 1999 CT demonstration of the 1996 AJCC–UICC regional lymph node classification of lung cancer staging. Radiographics 19: 900 25. Proto A V, Simmons J D, Zylak C J 1983 The anterior junction anatomy. CRC Crit Rev Diagn Imaging 19: 111–173 26. Proto A V, Simmons J D, Zylak C J 1983 The posterior junction anatomy. CRC Crit Rev Diagn Imaging 20: 121–173 27. Cimmino C V 1981 The oesophageal–pleural stripe: an update. Radiology 140: 607–613 28. Bachman A L, Teixidor H S 1975 The posterior tracheal band: a reflection of local mediastinal abnormality. Br J Radiol 48: 352–359 29. Keats T E 1975 The aortic–pulmonary mediastinal stripe. Am J Roentgenol 116: 107–109 30. Blank N, Castellino R A 1972 Patterns of pleural reflections of the left superior mediastinum: normal anatomy and distortions produced by adenopathy. Radiology 102: 585–589 31. Lane E J, Heitzman E R, Dinn W M 1976 The radiology of the superior intercostal veins. Radiology 120: 263–267 32. Abiru H, Ashizawa K, Hashmi R et al 2005 Normal radiographic anatomy of thoracic structures: analysis of 1000 chest radiographs in Japanese population. Br J Radiol 78: 398–404 33. Whalen J P, Meyers M A, Oliphant M et al 1973 The retrosternal line. Am J Roentgenol 117: 861–872 34. Lennon E A, Simon G 1965 The height of the diaphragm in the chest radiograph of normal adults. Br J Radiol 38: 937–943 35. Houston J G, Morris A D, Howie C A et al 1992 Quantitative assessment of diaphragmatic movement: a reproducible method using ultrasound. Clin Radiol 46: 405–407 36. Berkman Y M, Davis S D, Kazam E 1989 Right phrenic nerve: anatomy, CT appearance, and differentiation from the pulmonary ligament. Radiology 173: 43–46 37. Ujita M, Ojiri H, Arizumi M et al 1993 Appearance of the inferior phrenic artery and vein on CT scans of the chest: a CT and cadaveric study. Am J Roentgenol 160: 745–747

CHAPTER

The Chest Wall, Pleura, Diaphragm and Intervention

13

John A. Verschakelen

The chest wall • Soft tissues • Bony structures The pleura • Pleural effusion

• Pneumothorax • Pleural thickening and fibrothorax • Pleural calcification • Pleural tumours The diaphragm

THE CHEST WALL Although there is a wide variety of tissues and structures that make up the chest wall, based on their radiographic presentation, its components can be grouped into two major parts: the soft tissues and the bony structures.

SOFT TISSUES On the chest radiograph the soft tissues present as areas of increased density that in part project next to the bony chest wall and in part overlay the different components of the chest. Abnormalities of the soft tissues will present as an abnormal increase or decrease in density often combined with the appearance of an abnormal contour or the disappearance of a normal contour. Because of better density resolution and multiplanar reformatting, computed tomography (CT) can better demonstrate the different tissues of the chest wall. CT has the advantage over magnetic resonance imaging (MRI) of higher spatial resolution and the ability to better identify bony structures. MRI, however, yields greater soft tissue contrast which can be important1,2. Multiplanar imaging and three-dimensional (3D) reformation can be performed with both techniques.

Ultrasound may also be used to examine the chest wall. In general it provides less detailed and comprehensive information but it usually enables the lesion to be localized, allows a distinction to be made between cystic and solid lesions, and enables guided aspiration/biopsy to be performed under imaging control.

Breasts On the female chest radiograph it is mandatory to check that both breasts are present. Unilateral radical mastectomy is usually easy to detect because it generates a unilateral mid/lower zone transradiancy and an abnormally straight anterior axillary fold that passes upwards and inwards towards the mid clavicle (Fig. 13.1). Bilateral radical mastectomy is more difficult to identify, but an overall increase in basal transradiancy and axillary fold abnormalities should provide adequate clues. Surgical interventions short of radical mastectomy may be impossible to detect, but close attention to the relative transradiancy of the breast regions and to the breast contours may provide suggestive findings. Nipple shadows can mimic intrapulmonary nodules. A putative nipple should be checked for compatible size (5– 15 mm), shape and location—its relation to the breast outline in a woman or the pectoralis opacity in a man.

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Figure 13.1 Left mastectomy. The left hemithorax is more transradiant than the right.

Muscles On the chest radiograph the pectoralis major produces a broad, band-like opacity extending downwards and medially from the axilla. Unilateral absence or hypoplasia of the pectoralis major results in a unilateral transradiancy and an abnormal anterior axillary fold as seen with mastectomy. In Poland’s syndrome these changes are accompanied by ipsilateral hand and arm anomalies (particularly syndactyly) with or without absence of pectoralis minor, rib anomalies, and hypoplasia of breast and nipple.

Soft tissue calcification Soft tissue calcification may occur in the chest wall, and clues to its site and nature are provided by its morphology distribution and the clinical history. Possible causes to consider include granulomatous lymph nodes, parasites (Taenia solium and Dracunculus medinensis), calcinosis universalis, childhood dermatomyositis, tuberculosis (spine, ribs, or soft tissues) and bone neoplasms. Ossification is rare and most commonly seen in fibrodysplasia ossificans progressiva.

Subcutaneous emphysema Subcutaneous emphysema of the chest wall is not uncommon following surgery, pleural drain placement, trauma, or in cases of spontaneous or acquired pneumomediastinum. Air dissects along tissue planes and between muscle bundles, giving an overall pattern of linear transradiancies which can significantly interfere with the interpretation of the underlying structures. In this way diagnosis of pneumothorax can become very difficult. In case of doubt CT can be performed.

Soft tissue tumours A soft tissue tumour of the chest wall gives rise to an opacity. Malignant and inflammatory lesions cause bony destruction and

benign ones result in rib separation and notch-like remodelling from pressure erosion. The most common benign chest wall tumour is a lipoma, but a variety of other mesenchymal tumours occur, including neurofibromas (focal or plexiform), neurilemmomas, haemangiomas and lymphangiomas (cystic hygromas). On CT, lipomas are well-demarcated homogeneous masses of low density (−90 to −150 HU).They contain few, if any, other soft tissue components; the presence of the latter in a fatty tumour suggests a liposarcoma. MRI features are also characteristic, with high signal on T1-weighted images, intermediate signal on T2-weighted images, and low signal with fat suppression1,2. Neurofibromas on CT characteristically have a lower density than muscle both before and after intravenous contrast medium. On MRI, neurofibromas give low to intermediate signal on T1-weighted images but high signal on T2-weighted images and marked contrast enhancement after gadolinium, which allows clear delineation of their extent. Haemangiomas are uncommon lesions that occasionally show phlebolithic calcification on plain radiography. Findings on CT include phleboliths, bone remodeling, and an enhancing mass. MRI is the best investigation for delineating their extent. Lesions give an intermediate signal on T1-weighted images and a high signal on T2-weighted images, accompanied by inhomogeneities generated by vessels, soft tissue, and elements derived from haemorrhage1,2. Lymphangiomas on CT have the features of a fluid-filled cyst with or without septation. On MRI they have the features of a cyst with low protein content. Malignant primary tumours arising in the soft tissues of the chest wall are unusual, the most common being lipo- or fibrosarcomas. Secondary tumours of the chest wall are common, particularly when due to local spread (carcinoma of the breast and lung, lymphoma) (Fig. 13.2); see bronchial carcinoma and Pancoast’s tumour, below.

BONY STRUCTURES Although depicting bone abnormalities is not the primary goal of a chest radiograph, the bony structures that are, as a result of the technique, often only partially visible should be carefully examined. CT, when indicated, is better at demonstrating congenital or acquired remodelling or complicated fractures; multidetector 2D or 3D reformations can be helpful.

Ribs There are normally 12 pairs of ribs. Cervical ribs occur in 1–2% of the population and are commonly bilateral, though often asymmetrical. Congenital abnormalities of modelling may be confined to one or two ribs or be generalized. One or a few upper ribs are commonly bifid, splayed, fused, or hypoplastic. Usually occurring in isolation, these anomalies are occasionally part of a syndrome (e.g. basal cell naevus syndrome) or associated with other anomalies (e.g. Sprengel’s deformity). With acquired remodelling, abnormalities tend to be focal, affecting one or many ribs. Such acquired changes may follow

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Figure 13.2 Invasive malignant T-cell lymphoma. (A) High-resolution chest wall ultrasound image through the intercostal space showing echoic cortical rib and consecutive echo void behind. Within the intercostal space hypo-echoic tumour tissue (arrowheads) is seen invading the posterior chest wall. (B) Same patient, transverse contrast-enhanced CT. Enhancing peripheral tumour tissue is widely invading the posterior chest wall. Exact definition of invasive tissue is impaired owing to low soft tissue contrast resolution in CT. (C) Same patient, sagittal T1-weighted MRI pre- (left) and post- (right) contrast medium nicely display the widespread invasion of the posterior chest wall by enhancing tumour tissue. There is already invasion of two ribs, including cortical rib destruction (arrowheads). The central nonenhancement of the tumour is due to necrosis. (Courtesy of Dr R. Bittner.)

fracture, surgery, osteomyelitis and empyema drainage, or result from external pressure (rib notching). The two main causes of rib notching are coarctation of the aorta and neurofibromatosis Type I. Ribs may fracture and the callus formed can sometimes mimic an intrapulmonary opacity. Destructive rib lesions occur most commonly in osteomyelitis or neoplastic disease. The former is uncommon and may be haematogenous (e.g. staphylococcal or tuberculous) or caused by direct spread from lung and pleural space (e.g. in actinomycosis). Bronchial carcinoma, including Pancoast’s tumour, commonly spreads from lung to rib. In this latter condition MRI can be performed to study the extent of the disease, especially the relationship between the tumour and the plexus brachialis in case of a Pancoast’s tumour3 (Fig. 13.3). Multidetector CT (MDCT) can also play an important role especially because it can better evaluate the invasion in the bony cortex of the ribs4 (Fig. 13.3D). Also, 3D image reconstruction methods can be used in selected cases to clarify a complex relationship between the tumour invading the chest wall and vascular structures of the thoracic inlet. Various primary and secondary tumours can affect ribs, causing localized lesions. Benign primary tumours are infrequent, and of these, the cartilaginous tumours (chondromas, osteochondromas) are the most common. They are predominantly anterior and may show characteristic cartilaginous calcification. Other lesions that broadly fall into this category include fibrous dysplasia, histiocytosis X, haemangioma and aneurysmal bone cyst1 (Fig. 13.4). The most common malignant rib tumours are metastatic deposits and myeloma. Primary malignant tumours are rare, chondrosarcomas being the least uncommon. Other malignancies that occur occasionally include lymphoma, osteosarcoma and round-cell tumours.

Sternum This is well displayed in a lateral chest radiograph but is inconspicuous in the frontal projection, in which only the manubrial margins are sometimes visible, giving rise to confusing shadows that may mimic mediastinal widening. Various sternal deformities are described, and the most important radiologically is the depressed sternum (funnel chest, pectus excavatum) in which there is approximation of the lower half of the sternum and the spine (Fig. 13.5). This may be an isolated abnormality or it may be associated with other disorders such as Marfan’s syndrome or congenital heart disease (particularly atrial septal defect [ASD]). The radiological signs on a postero-anterior (PA) chest radiograph consist of a shift of the heart to the left, straightening of the left heart border with prominence of the main pulmonary artery segment, loss of the descending aortic interface, and an increased opacity in the right cardiophrenic angle, often accompanied by a loss of clarity of the right heart border which simulates right middle lobe disease. The diagnosis can be suspected on a PA radiograph from the steep inferior slope of the anterior ribs and undue clarity of the lower dorsal spine seen through the heart. Pigeon chest (pectus carinatum) represents the reverse deformity and may be congenital or acquired. Neoplasms of the sternum are usually malignant (myeloma, chondrosarcoma, lymphoma or metastatic carcinoma), the most common benign tumour being a chondroma. Non-neoplastic processes that may affect the sternum include osteomyelitis, histiocytosis X, Paget’s disease, fibrous dysplasia, osteitis fibrosa cystica and intersternocostoclavicular hyperostosis. CT is the best investigation for imaging the sternum because it eliminates overlapping structures, detects bony destruction, allows imaging of adjacent soft tissues (the parasternal–internal mammary zone), and has good contrast resolution superior to that of conventional radiography or tomography.

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Figure 13.3 Pancoast’s tumour. (A,B) MRI. (A) Coronal and (B) sagittal image. Large tumour in the left upper lobe invading the soft tissues and displacing the vascular structures anteriorly (arrows). The brachial plexus has also been invaded (arrowheads). (C,D) CT (different patient). (C) Coronal and (D) sagittal image bone window setting. Large tumour in the left upper lobe invading the soft tissues, displacing and invading the left subclavian artery and invading a rib (arrow).

Clavicles The medial clavicular ends are important landmarks used together with the spine in assessing rotation on a radiograph. The joints at both ends are synovial but only the acromioclavicular joint can be assessed with confidence on a chest radiograph. It may be eroded in any synovitis, particularly rheumatoid arthritis, and is also commonly fuzzy and illdefined in hyperparathyroidism and rickets. Neoplasms of the clavicle are usually malignant (myeloma or metastatic). Other

primary tumours and tumour-like lesions include osteosarcoma, Ewing’s sarcoma, post-radiation sarcoma, aneurysmal bone cyst, histiocytosis X and intersternocostoclavicular hyperostosis. Either CT or MRI is required to provide a full evaluation of the medial clavicular ends.

Spine Kyphoscoliosis makes assessment of the chest radiograph difficult and CT is often necessary to evaluate possible thoracic disease.

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Figure 13.4 Fibrous dysplasia in a rib; chest radiograph detail of the left lung. Compared with the other ribs the ninth rib shows an increase in density and is slightly broadened.

Figure 13.5 Depressed sternum. (A) PA chest radiograph. The depressed sternum displaces the heart to the left and rotates it so that the left heart border adopts a straight configuration. The right heart border becomes ill-defined and is bounded by a hazy opacity, simulating collapse of the right middle lobe. The ribs show their characteristic configuration—horizontal posteriorly and steeply oblique anteriorly. The posterior displacement of the sternum is better demonstrated on (B) the lateral chest radiograph and (C) the axial CT.

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THE PLEURA The chest radiograph is still the most important and widely used means of demonstrating and following the progress of pleural disease, though ultrasound, CT and MRI can play a significant role in a number of specific situations. Pleural disease is manifest by the accumulation of fluid or air in the pleural space, by pleural thickening (with or without calcification), or by the presence of a pleural mass.

and left effusions with pancreatitis, pericarditis, oesophageal rupture and aortic dissection. Massive effusions are most commonly due to malignant disease, particularly metastases (lung or breast), but may also occur in heart failure, cirrhosis, tuberculosis, empyema and trauma.

PLEURAL EFFUSION

Free pleural fluid A small amount of free fluid may be undetectable on an erect PA chest radiograph as it tends initially to collect under the lower lobes. Such small subpulmonary effusions can be demonstrated by ultrasound or CT. An alternative technique, the lateral decubitus chest radiograph has largely been replaced by these newer techniques6. As the amount of effusion increases, the posterior and then the lateral costophrenic angles become blunted, by which time a 200–500 ml effusion is present. Following this the classical signs develop, viz homogeneous opacification of the lower chest with obliteration of the costophrenic angle and the hemidiaphragm. The superior margin of the opacity is concave to the lung and is higher laterally than medially. Above and medial to the meniscus there is a hazy increase in opacity owing to the presence of fluid posterior and anterior to the lungs (Fig. 13.6). Massive effusions cause dense opacification of the hemithorax with contralateral mediastinal shift (Fig. 13.7). Absence of mediastinal shift with a large effusion raises the strong possibility of obstructive collapse of the ipsilateral lung or extensive pleural

A number of different types of fluid may accumulate in the pleural space, the most common being transudate, exudate (thin or thick), blood and chyle. Occasionally effusions are highly specific, not falling into any of the above categories and containing, for example, bile, cerebrospinal fluid, or iatrogenic fluids. All types of pleural effusion are radiographically identical, though historical, clinical and other radiological features may help limit the diagnostic possibilities. Sometimes, also CT and MRI can help to specify the diagnosis. Bilateral pleural effusions tend to be transudates because they develop secondary to generalized changes that affect both pleural cavities equally—a rise in capillary pressure or a fall in blood proteins, etc. Some bilateral effusions are exudates, however, and this is seen with metastatic disease, lymphoma, pulmonary embolism, rheumatoid disease, systemic lupus erythematosus (SLE), post-cardiac injury syndrome, myxoedema and some ascites-related effusions. Right-sided effusions are typically associated with ascites, heart failure and liver abscess,

Imaging pleural effusion5 Chest radiograph

Figure 13.6 Bilateral pleural effusion. (A) Erect and (B) supine chest radiograph. The pleural effusion obscures the diaphragm and both costophrenic angles. It has a curvilinear upper margin concave to lung and is higher laterally than medially. This is opposite to the findings on the supine chest radiograph where the pleural effusion is hardly visible as a hazy opacity affecting the lower part of the thorax. Note also that the costophrenic angles are not obscured and that the vascular opacities are preserved in the overlying lung.

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Figure 13.7 Massive pleural effusion with mediastinal shift to the left. (A) Chest radiograph and (B) CT coronal reconstruction. A massive effusion displaces the mediastinum to the left. CT shows the important pleural effusion together with the enhanced atelectatic left lung. Note also the depression of the right hemidiaphragm (arrows).

malignancy, such as may be seen with mesothelioma or metastatic carcinoma (Table 13.1). Large effusions sometimes cause diaphragmatic inversion, particularly on the left where the diaphragm lacks the support of the liver7. Although pleural fluid collects initially under the lung, it is unusual for it to remain localized in this site once its volume exceeds 200–300 ml.This does happen occasionally, however, and may be suspected from an erect PA and lateral radiograph. On a PA radiograph this subpulmonary effusion7 presents as a ‘high hemidiaphragm’ with an unusual contour that peaks more laterally than usual, has a straight medial segment and falls away rapidly to the costophrenic angle laterally, which may or may not be blunted. Ultrasound or CT will confirm the diagnosis (see Fig. 13.20). Loculated (encysted, encapsulated) pleural fluid Fluid can loculate between visceral pleural layers in fissures or between visceral and parietal layers, usually against the chest wall. It is unusual for this to happen without some additional radiographic clue to the presence of pleural disease (Fig. 13.8). Both ultrasound and CT can be used to distinguish loculated fluid from solid lesions.

Table 13.1

CAUSES OF OPACIFICATION OF A HEMITHORAX

Pleural effusion Consolidation Collapse Massive tumour Fibrothorax Combination of above lesions Pneumonectomy Lung agenesis

Pleural effusion in the supine patient In the supine patient, pleural fluid layers out posteriorly and the meniscus effect, present from front to back, is not appreciated because of the projection. The main radiographic finding is a hazy opacity like a veil affecting the whole or the lower part of the hemithorax, with preserved vascular opacities in the overlying lung (see Fig. 13.6B). Additional signs include haziness of the diaphragmatic margin, blunting of the costophrenic angle, a pleural cap to the lung apex, thickening of the minor fissure and widening of the paraspinal interface.

Ultrasound6,8 Pleural fluid, especially when it is a transudate, is commonly echo-free and marginated on its deep aspect by a highly echogenic line at the fluid–lung interface. Exudative and haemorrhagic effusions may be echogenic and are often accompanied by pleural thickening. The pattern of echoes may be homogeneous, complex or septated. Features that help distinguish a fluid from a solid echogenic lesion include changes in shape with breathing, the presence of septa and fibrous strands, and movement of components induced by breathing (Fig. 13.9). Occasionally, in the absence of such features, some echogenic fluid pleural effusions are indistinguishable from solid ones.6 Ultrasound has a number of important roles in the evaluation and management of pleural fluid. It can be used to distinguish between pleural fluid, solid pleural (or extrapleural) lesions, and peripheral lung lesions. In peripheral lung lesions, the presence of fluid bronchograms and vessels on Doppler examination will positively identify consolidation. In addition, pleural lesions characteristically make an obtuse angle with the chest wall, whereas with intrapulmonary lesions the angle is often acute.This ability of ultrasound to distinguish pulmonary lesions (collapse, consolidation, abscess) from pleural effusion

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Figure 13.8 Encapsulated fluid on (A) PA and (B) lateral chest radiographs. Pleural fluid is encapsulated in the major fissure and against the anterior chest wall. These encysted fluid collections can mimic a lung tumour.

extent and location of the latter. Accurate localization of such loculated effusions is useful before drainage. CT distinguishes between parenchymal lung disease and pleural disease, a distinction that is often facilitated by a bolus of intravenous contrast medium. CT can characterize the morphology of pleural thickening that often accompanies a pleural effusion, distinguishing between malignant thickening (nodular, with focal masses) and benign thickening, which is typically uniform. CT can also identify any underlying lung disease that might have provoked an effusion and it facilitates percutaneous aspiration and biopsy (Fig. 13.10).

Figure 13.9 Ultrasound of an empyema. The pleural fluid is separated by septa (arrows). Although the pleural fluid is echo-free in part, some areas return echoes owing to the turbid nature of the empyema fluid.

is particularly useful when it comes to the evaluation of the opaque hemithorax. Ultrasound can also be used to identify small amounts of pleural fluid, or pleural fluid in unusual locations, as with a subpulmonary effusion (see Fig. 13.20). Ultrasound is widely used to localize pleural fluid for aspiration and identify any solid components to allow guided biopsy. Furthermore, ultrasound may identify the cause of an effusion when it lies inside or even outside the chest (e.g. subphrenic abscess, metastasis).

Computed tomography6,9 CT is very sensitive in detecting pleural fluid and can distinguish between free and loculated fluid, identifying the

Figure 13.10 CT of malignant pleural disease. In this right pleural effusion CT identifies the extensive and irregular pleural thickening characteristic of a malignant process (pleural metastases). Note also the primary tumour in the right breast.

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A pleural effusion appears on CT as a dependent sickleshaped opacity with a lower CT number than that of any adjacent pleural thickening or mass. CT numbers do not allow a distinction between transudate and exudate. However, parietal pleural thickening at contrast-enhanced CT almost always indicates the presence of pleural exudates. The higher density of clotted blood in a haemothorax is sometimes apparent.The fat-containing chylothorax does not have a lower CT number than normal, because of its protein content. Loculated effusions have a lenticular configuration with smooth margins and they displace the adjacent parenchyma.

Magnetic resonance imaging6 MRI has a limited role in the evaluation of pleural effusion. Pleural fluid has a low signal on T1-weighted sequences and a high signal on T2-weighted images, with a tendency for exudates to give a higher signal than transudates on T2-weighted sequences. In addition, complex exudates have greater signal intensity than simple exudates. It may also be possible to differentiate transudates from exudates using triple echo-pulse sequence, and benign from malignant changes using high-resolution MRI.10 Chylous effusion can cause high signal intensity on T1-weighted images similar to subcutaneous fat. In the subacute and chronic stage, haematomas show bright signal intensity on T1-weighted images, surrounded by a dark rim caused by haemosiderin.

Some specific pleural effusions Exudates and transudates Pleural effusion is common in heart failure and tends to be more frequent and larger on the right. All types of pericardial disease may be associated with pleural effusion which is predominantly left sided. Pleural effusion is a characteristic finding in the post-cardiac injury syndrome, seen in about 80% of patients. It may be bilateral or unilateral and is commonly accompanied by consolidation and pericardial effusion. Pulmonary embolism is commonly associated with pleural effusion which is seen in 25–50% of cases. A number of drugs have been described as causing pleural effusions. The most common agents are cytotoxics (methotrexate, procarbazine, mitomycin, busulphan, bleomycin and interleukin-2), nitrofurantoin, antimigraine drugs (ergotamine, methysergide), amiodarone, propylthiouracil, bromocriptine and gonadotropins. With a number of these agents pleural thickening is more common than a pleural effusion. Pleural effusion is also a recognized complication of hepatic cirrhosis. The principal mechanism of its production is the transdiaphragmatic passage of ascites, though other factors such as hypoalbuminaemia may contribute in a small number of cases. Both acute and chronic pancreatitis are associated with pleural effusions which have high amylase levels. In acute pancreatitis, exudative and often blood-stained effusions form in 15% of patients, particularly on the left side where the diaphragm is closely related to the pancreatic tail. Associated elevation of the hemidiaphragm and basal lung consolidation are common. In chronic pancreatitis, effusions tend to be large and recurrent and patients present with dyspnoea, unlike effusions in acute

• THE CHEST WALL, PLEURA, DIAPHRAGM AND INTERVENTION

pancreatitis in which abdominal symptoms predominate. The pathogenesis of pleural effusion in chronic pancreatitis is fistula formation following ductal rupture. Pleural effusion is common with subphrenic abscess and occurs in about 80% of patients. The effusion is often accompanied by basal lung collapse and consolidation, an elevated hemidiaphragm and a subdiaphragmatic air–fluid level. Pleural effusion may occur in a number of renal conditions. Exudative effusions may be seen in uraemia and are often accompanied by pericarditis. Effusions can be large or small and are often unilateral, behaving in a rather indolent fashion. In common with other hypoproteinaemic states, bilateral effusions develop in about 20% of patients with nephrotic syndrome. Peritoneal dialysis can produce pleural effusions by the direct transdiaphragmatic passage of fluid, as occurs with cirrhotic ascites. In common with other ascites-related effusions they are predominantly right sided, but these effusions have a diagnostically high level of glucose. Patients with acquired immune deficiency syndrome are at risk for a variety of pleural infections and neoplasms that can be associated with pleural effusion. These effusions are most frequently caused by pneumonic infections but can also be the result of non-Hodgkin’s lymphoma. Empyema is a suppurative exudate usually parapneumonic. Less commonly it is caused by transdiaphragmatic extension of a liver abscess or by bronchopleural fistula (Fig. 13.11).

Bronchopleural fistula Bronchopleural fistula differs from a pneumothorax in that the communication with the pleural space is via airways rather than distal air spaces. It occurs in two main settings, following partial or complete lung resection and in association with necrotizing infections.

Figure 13.11 Empyema. An enhanced CT shows a fluid collection in the right pleural space. The pleura is thickened but smooth and enhancing. The empyema followed pneumonia. Soft tissue medially is collapsed and consolidated lung. Note the oedema of the extrapleural fat.

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Chylothorax Chylous effusions are commonly milky because they contain triglycerides in the form of chylomicrons. Chylous and non-chylous pleural effusions are indistinguishable on the chest radiograph. In addition, despite its high fat content, the increased protein level of a chylothorax gives it an attenuation on CT similar to that of other pleural effusions. Chylous effusion can cause high signal intensity on T1-weighted images similar to subcutaneous fat. Chyle collects in the pleural space following rupture of the thoracic duct or seepage from collaterals. Rarely, it crosses the diaphragm from the abdomen in the presence of chylous ascites.

Haemothorax On the plain chest radiograph an acute haemothorax is indistinguishable from other pleural fluid collections. Once the blood clots there is a tendency for loculation and occasionally a fibrin body will form. Pleural thickening and calcification are recognized sequelae. On CT a haemothorax may show areas of hyperdensity, and in the subacute or chronic stage it will appear on MRI as a high signal on T1- and T2-weighted images, possibly with a low signal rim caused by haemosiderin. The most common cause of haemothorax is trauma, but it is seen in a number of other conditions, including ruptured aortic aneurysm, pneumothorax, extramedullary haemopoiesis and coagulopathies.

Table 13.2

CAUSES OF ADULT PNEUMOTHORAX

Spontaneous, primary Spontaneous, secondary Airflow obstruction

Asthma Chronic obstructive pulmonary disease Cystic fibrosis

Pulmonary infection

Cavitary pneumonia Tuberculosis Fungal disease AIDS Pneumatocoele

Pulmonary infarction Neoplasm Diffuse lung disease

Metastatic sarcoma Histiocytosis X Lymphangioleiomyomatosis Fibrosing alveolitis Other diffuse fibroses

Hereditable disorders of fibrous connective tissue

Marfan’s syndrome

Endometriosis (catamenial pneumothorax)

Traumatic, noniatrogenic Ruptured oesophagus/trachea Closed chest trauma (± rib fracture) Penetrating chest trauma

PNEUMOTHORAX

Traumatic, iatrogenic Thoracotomy/thoracocentesis

Air in the pleural space is a pneumothorax. When air and liquid are present the nomenclature depends on their relative volumes and the type of liquid. Small amounts of liquid are disregarded and the condition is still called a pneumothorax; otherwise the prefix hydro-, haemo-, pyo- or chylo- is added, depending on the nature of the liquid.

Primary spontaneous pneumothorax Iatrogenic causes apart, the most common type of pneumothorax in the adult is the so-called primary spontaneous pneumothorax (PSP). A pneumothorax occurring without an obvious precipitating event is spontaneous, and if the patient has essentially normal lungs it is in addition primary. PSP occurs predominantly in young adults (65% are between 20 and 40 years of age) and it is five times more common in men than women. Untreated, at least one-third of patients will have a recurrence, most commonly within a few years and on the ipsilateral side. PSP is nearly always caused by the rupture of an apical pleural bleb. Although not detectable on interval chest radiographs, one taken at the time of the pneumothorax will show one or more blebs projecting from the apical lung margin in 20% of patients; such abnormal apical airspaces are much more commonly shown by interval CT.11

Secondary spontaneous pneumothorax A large number of conditions predispose to pneumothorax (Table 13.2). In a number of these disorders pneumothorax occurs frequently.

Percutaneous biopsy Tracheostomy Central venous catheterization

Diagnosis The diagnosis of pneumothorax is made with the chest radiograph, which also detects complications and predisposing conditions and helps in management5 (Fig. 13.12).

Typical signs These are seen on erect radiographs in which the pleural air rises to the lung apex. Under these conditions the visceral pleural line at the apex becomes separated from the chest wall by a transradiant zone devoid of vessels. Though this sounds a straightforward sign to assess, difficulties of interpretation can arise with avascular lung apices, as in bullous disease and when linear shadows are created by clothing or dressing artefacts, tubes and skin folds. Skin folds cause problems particularly in neonates and in old people radiographed slumped against a cassette in the AP projection (Fig. 13.13) Features that help identify artefacts and skin folds include extension of the ‘pneumothorax’ line beyond the margin of the chest cavity, laterally located vessels, and an orientation of a line that is inconsistent with the edge of a slightly collapsed lung. In addition, the margin of skin folds tends to be much wider than the normally thin visceral pleural line. In indeterminate circumstances a repeat

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Figure 13.13 Skin folds mimicking a right pneumothorax (arrows). The laterally located blood vessels, the wide margin of the lines, and the orientation of the lines that is inconsistent with the edge of a slightly collapsed lung help to differentiate them from a real pneumothorax.

chest wall at the apex or laterally. Signs that suggest a pneumothorax under these conditions are12,13 (Fig. 13.14): • ipsilateral transradiancy, either generalized or hypochondrial • a deep, finger-like costophrenic sulcus laterally • a visible anterior costophrenic recess seen as an oblique line or interface in the hypochondrium; when the recess is manifest as an interface it mimics the adjacent diaphragm (‘double diaphragm sign’) • a transradiant band parallel to the diaphragm and/or mediastinum with undue clarity of the mediastinal border • visualization of the undersurface of the heart, and of the cardiac fat pads as rounded opacities suggesting masses • diaphragm depression.

Figure 13.12 Left primary spontaneous pneumothorax. Chest radiograph (A) at deep inspiration and (B) at deep expiration. The left lung has partially collapsed and an area of extreme low density without vascular markings becomes visible. The pneumothorax is accentuated on the chest radiograph at suspended deep expiration (B).

chest radiograph, an expiratory radiograph (see Fig. 13.12B) or one taken with the patient decubitus may clarify the situation. Should doubt still remain, then CT is particularly helpful in distinguishing between bullae and a pneumothorax.

In a patient who cannot stand, the presence of a pneumothorax can be confirmed with a lateral decubitus view or a supine decubitus projection with the cassette placed dorsolaterally at 45 degrees and the X-ray tube angled perpendicular to the cassette. When the pleural space is partly obliterated a pneumothorax may be loculated, and must be differentiated from other localized transradiancies. These include cysts, bullae, pneumatocoeles, pneumomediastinum and local emphysema. These cannot always be differentiated by plain radiographs, but can be by CT.

Atypical signs

Complications Haemopneumothorax

These arise when the patient is supine or the pleural space partly obliterated. In the supine position, pleural air rises and collects anteriorly, particularly medially and basally, and may not extend far enough posteriorly to separate lung from the

This is a common complication of traumatic pneumothorax. Small amounts of serous or bloody fluid may also occur with a spontaneous pneumothorax but only 2% of individuals develop a clinically significant haemothorax in these circumstances.

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Figure 13.14 Supine pneumothorax. Portable chest radiograph (A) before and (B) immediately after development of a pneumothorax. There is an increase of transradiancy at the left lung base, the costophrenic sulcus laterally is more pronounced, and the diaphragm is slightly depressed.

Blood may clot in the pleural space, producing a mass which can mimic a pleural tumour.

Tension pneumothorax This life-threatening complication is present when intrapleural pressure becomes positive relative to atmospheric pressure for a significant part of the respiratory cycle. Tension has an adverse effect on gas exchange and cardiovascular performance, causing a rapid deterioration in the patient’s clinical condition. The diagnosis is usually made clinically and treatment instituted without a radiograph. Should a chest radiograph be taken, it will show contralateral mediastinal shift and ipsilateral diaphragm depression. Mild degrees of contralateral mediastinal shift are not unusual with a nontension pneumothorax because of the negative pressure in the normal pleural space. Moderate or gross mediastinal shift, however, should be taken as indicating tension, particularly if the ipsilateral hemidiaphragm is depressed.This latter sign is the more reliable and is almost invariably present with significant tension.

Pyopneumothorax This unusual complication is seen most commonly following necrotizing pneumonia or oesophageal perforation.

Adhesions These generate straight band shadows extending from the lung margin to the chest wall. They limit collapse but at the same time may account for continued air leakage from the lung surface, and if they tear they may bleed. They can be identified with CT.

Re-expansion oedema This unusual complication is sometimes seen following the rapid therapeutic re-expansion of a lung that has been markedly collapsed for several days or more. Oedema comes on within hours of drainage, may progress for a day or two and clears within a week. It usually causes only mild morbidity.

PLEURAL THICKENING AND FIBROTHORAX5 Pleural thickening is common and usually represents the organized end stage of various active processes such as infective and noninfective inflammation (including asbestos exposure and pneumothorax) and haemothorax. When generalized and gross, it is termed a fibrothorax and may cause significant ventilatory impairment. Radiologically, pleural thickening gives fixed shadowing of water density, most commonly located in the dependent parts of the pleural cavity. Viewed en profile, it appears as a band of soft tissue density up to approximately 10-mm thick, more or less parallel to the chest wall and with a sharp lung interface. En face, it causes ill-defined, veil-like shadowing. Blunting of the costophrenic angle, often with tenting of the diaphragm, is a common finding. On ultrasound, benign pleural thickening produces an homogeneous echogenic layer just inside the chest wall. It is not reliably detected unless it is 1 cm or more thick. CT on the other hand is very sensitive at detecting pleural thickening, which is most easily assessed on the inside of the ribs, where there should normally be no

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soft tissue opacity. In chronic conditions pleural thickening is commonly accompanied by thickening of the normally inconspicuous fatty layer that lies immediately outside the parietal pleura, a feature that can be appreciated on CT. Fibrous pleural thickening is common in the apical pleural cupola. This may be secondary to tuberculosis or represent apical cap. Caps are age-related changes of unknown aetiology. Sometimes they have a scalloped contour or are associated with a tenting towards the lung. They are as commonly unilateral as bilateral. Caps should be distinguished from the companion shadows of the upper ribs, from extrapleural linear fat deposition and most importantly from a Pancoast’s tumour. Companion shadows of the ribs are usually smoothly bordered towards the lung apex while extrapleural fat is usually bilateral, symmetrical, and also located along the lateral chest wall. Caps may be indistinguishable from Pancoast’s tumour on the chest radiograph. In case of doubt CT or MR should be performed. Fibrous pleural thickening can be induced by asbestos exposure14 (Fig. 13.15). This thickening can be diffuse or is more often multifocal. These pleural plaques can undergo

• THE CHEST WALL, PLEURA, DIAPHRAGM AND INTERVENTION

hyaline transformation, calcify, or ossify. They are most commonly found along the lower thorax and on the diaphragmatic pleura. On CT, they appear as circumscribed areas of pleural thickening separated from the underlying rib and extrapleural soft tissues by a thin layer of fat. Because of their higher density they can easily be differentiated from circumscribed increase of extrapleural fat, as sometimes seen in obese patients. Diffuse pleural thickening is also a manifestation of asbestos exposure. The radiographic definition of diffuse pleural thickening or fibrothorax is somewhat arbitrary. It has been suggested to consider as fibrothorax a smooth uninterrupted pleural density that extends over at least one-quarter of the chest wall. On CT fibrothorax has been defined as a pleural thickening which extends more than 8 cm in the craniocaudal direction, 5 cm laterally and with a thickness of more than 3 mm. Common causes of fibrothorax are empyema, tuberculosis and haemorrhagic effusion. Asbestos exposure-related fibrothorax is less common than pleural plaques and is usually the sequel of a benign exudative effusion. CT may be helpful

Figure 13.15 (A–D) Pleural plaques caused by asbestos exposure. Pleural plaques are most commonly found along the lower thorax, on the diaphragmatic pleura and, when involvement is extensive, also along the lateral and anterior thorax (arrows). They can partially or completely calcify or ossify.

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to find the aetiology of the fibrothorax. Extensive calcification favours previous tuberculosis or empyema5 (Fig. 13.16). Asbestos exposure-related fibrothorax is usually bilateral and rarely calcified. Generalized, postinflammatory pleural thickening must be distinguished from diffuse pleural malignancy caused by mesothelioma, metastatic disease (particularly adenocarcinoma), lymphoma and leukaemia. Mesothelioma and adenocarcinoma cause diffuse pleural thickening which is often lobulated, and may surround the whole lung and extend into and along fissures. These features are frequently obscured by an effusion. The most useful signs on CT that indicate malignant as opposed to benign pleural thickening are circumferential thickening, nodularity, parietal thickening of more than 1 cm, and involvement of the mediastinal pleura5 (see Figs 13.18, 13.19). MRI signal intensity seems to be a valuable additional feature for differentiating benign from malignant disease, especially since MRI is often able to demonstrate the tumour extension into the chest wall. Signal hypointensity with long TR sequences is a reliable predictive sign of benign pleural disease15.

PLEURAL CALCIFICATION Pleural calcification is most commonly seen following asbestos exposure, empyema (usually tuberculous) and haemothorax (Fig. 13.16). In the last two conditions, calcification is irregular, resembles a plaque or sheet, and is contained within thickened pleura. It may occur anywhere but is most common in the lower posterior half of the chest and is usually unilateral, unlike that found in silicosis, particularly of the asbestos-related type, where calcification occurs as more discrete collections within plaques and is usually bilateral.

PLEURAL TUMOURS Localized pleural tumours16 These are relatively uncommon, the most common being a localized fibrous tumour (localized mesothelioma) (Fig.

13.17). These lesions most commonly present in middle age, about half the patients being asymptomatic. Hypertropic osteoarthropathy is a well-recognized complication (10–30% of patients) and uncommonly the tumour produces hypoglycaemia. Microscopically two-thirds are benign and one-third is malignant.The plain radiographic findings are of a pleurallybased, well-demarcated, rounded and often slightly lobulated mass (2–20-cm diameter) which may, because of pedunculation, show marked positional variation with changes in posture and respiration. Pleural fibromas usually make an obtuse angle with the chest wall and may reach enormous sizes. Occasionally they may arise in a fissure. CT findings are similar to those observed on plain radiography: a mobile mass, often heterogeneous because of necrosis, haemorrhage, frequently enhancing after contrast medium administration, and rarely calcified. Malignant types are usually larger than 10 cm and may invade the chest wall. Typically these tumours show low signal intensity on both T1- and T2-weighted images, although tumours with intermediate to high signal intensity have been described.17 Lipomas are asymptomatic benign tumours that are usually discovered incidentally on chest radiographs as sharply defined pleural masses. Diagnosis is easy with CT because this examination can delineate the pleural origin and the fatty composition. This fatty density is homogeneous. When heterogeneous and when also soft tissue attenuation components are found, a liposarcoma should be suspected. Pleural lipomas have high signal intensity on T1-weighted images. On T2-weighted images signal is moderately bright. Diagnosis of pleural extension of bronchogenic carcinoma on a chest radiograph is very difficult.The only reliable indicator is rib destruction.With CT and MRI also diagnosis can be difficult. Features such as a large contact (> 3 cm) between the mass and the pleura, an obtuse angle between the tumour and the chest wall, an associated pleural thickening and the presence of pleural tags usually considered as signs of chest wall invasion also occur in benign lesions. The accuracy of CT can be increased by performing 2D and 3D reconstructions.

Figure 13.16 Pleural calcification. (A,B) On the chest radiograph an extensive sheet-like calcification of the right pleura with additional pleural thickening (old tuberculous empyema) is seen. (C) CT demonstrates the extent and thickness of the pleural calcification (arrow).

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Figure 13.17 Benign pleural fibroma. (A) Frontal and (B) lateral radiographs show a small well-demarcated, homogeneous, slightly lobulated mass (arrows). (C) CT shows that the mass is pleural based, sharply defined, and slightly enhancing.

In cases where tumour invasion is obvious, 2D sagittal or coronal reconstructions can be helpful in ascertaining the extent of the mass. MRI has a slight advantage over CT in the evaluation of chest wall and pleura invasion. Before spiral CT, MRI was considered better for studying superior sulcus tumours and their extension to the chest wall (see Fig. 13.3). However, studies have shown that spiral CT and MRI showed comparable sensitivity but that spiral CT had higher specificity. CT is superior in the detection of pleural calcifications and osseous destruction (see Fig. 13.3D). MDCT can also be used in selected cases to clarify a complex relationship between tumour invading the chest wall and vascular structures of the thoracic inlet. Pleural metastases are the most common pleural neoplasms. They are usually an adenocarcinoma with sites of origin including the ovary, stomach, breast and lung. Pleural metastatic disease can present as a solitary mass but more often multiple pleural locations are seen (Fig. 13.18). Pleural metastases are very often accompanied by pleural effusion, which can be the only finding on a chest radiograph. CT, MRI and ultrasound are more sensitive to demonstrate pleural metastasis as the cause of the pleural effusion.9

On CT malignant mesothelioma presents as a nodular soft tissue mass sometimes with hypodense areas corresponding with necrosis. Metastatic enlargement of hilar and mediastinal nodes is seen in up to 50% of patients. Malignant mesothelioma has a minimally increased signal on T1 and a moderately increased signal on T2. MRI may be superior to CT in determining extent of disease because it allows better evaluation of the relationship of the tumour to the structures of the chest wall, mediastinum and diaphragm. However,

Diffuse pleural tumours Diffuse tumoural thickening of the pleura can be caused by malignant mesothelioma or by pleural metastasis. Both entities are usually indistinguishable with imaging. Diffuse malignant mesothelioma is a rare primary neoplasm and its development is strongly related to asbestos exposure. It presents on a chest radiograph as an irregular and nodular pleural thickening with or without associated pleural effusion. Tumour extension into the interlobular fissures, accompanying pleural effusion, and invasion into the chest wall are better appreciated with CT (Fig. 13.19).

Figure 13.18 Malignant pleural thickening caused by metastatic disease. Malignant pleural thickening was caused by pleural metastases. Note the compression on the right hemidiaphragm and the extension of the tumour into the liver (arrows).

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lesion is adjacent to major cardiovascular structures, such as the aorta.21

Ultrasound Ultrasound is well suited for interventional procedures in the pleura. Because of the development of high-resolution, highfrequency probes with special biopsy ports, ultrasound guided biopsy of small pleural lesions has become possible22. Ultrasound is particularly indicated to guide percutaneous aspiration and catheter drainage of a pleural fluid or air collection, even in small amounts. Advantages of this technique include real-time visualization during needle placement, absence of ionizing radiation, and in the case of biopsy of a mass, the ability to target non-necrotic portions for sampling20. In addition, ultrasound is a safe and convenient method of guiding interventional procedures at the bedside of the patient and obviates the need to transport patients on life support devices to the radiology department. A disadvantage is that ultrasound is limited by attenuation of the beam as it transverses air-filled lung or pleura.

Computed tomography

Figure 13.19 Malignant mesothelioma. (A, B: axial and coronal CT) Diffuse lobulated and nodular thickening of the pleura with tumour extension into the lobar fissure (arrows). Note the metastatic enlargement of some hilar and mediastinal lymph nodes.

in most cases CT and MRI provide similar information. Ultrasound may be a supplementary method for biopsy and surgery planning.18,19

Pleural interventions Fluoroscopy Uni- or bi-planar fluoroscopy was the first imaging technique used to guide percutaneous pleural interventions. The technique is widely available, allows real-time control of the procedure, and gives an overview of the thorax. In addition, the technique is familiar to most investigators.20 However, fluoroscopy is not suitable for every lesion. Small lesions may be difficult or impossible to identify. Some lesions may be superimposed on or not separable from normal thoracic structures. Another important limitation is that biopsy or drainage using fluoroscopic guidance may not be advisable if the

Major advantages of CT over fluoroscopy are its multiplanar capabilities and its exquisite anatomical detail. CT is particularly useful for sampling lesions visible in only a single radiographic projection or when great imaging detail is required for the interventional procedure. The administration of intravenous contrast medium is mandatory for the identification of tissue necrosis, fluid content, and identification of normal and abnormal vascular structures. CT allows for determination of an optimal cutaneous entry point for the biopsy needle or for tube placement. Disadvantages of CT guided interventional procedures include greater patient discomfort lying on the CT table and greater expense than with fluoroscopically guided biopsies. A disadvantage compared to ultrasound is the fact that this technique also requires ionizing radiation. However, the introduction of CT continuous imaging, also called CT fluoroscopy, has improved the ease of performing interventional thoracic procedures because it allows real-time visualization of the lesion and of the progression of the needle or tube23. Compared with conventional spiral CT, there is also a markedly decreased patient radiation dose because the procedure can be shortened.

Magnetic resonance imaging Although MRI is often used for guidance of interventional procedures, little experience has been gained in thoracic or pleural interventions24. This technique combines the absence of ionizing radiation with good anatomical detail and has become possible with the introduction of non-ferromagnetic MRI compatible biopsy needles. Major disadvantages, however, include high cost, limited availability, the length of the procedure and the lack of real-time control.

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THE DIAPHRAGM The diaphragm is only seen because there is air-containing lung adjacent to it superiorly. It is 2–3-mm thick, but this will only be appreciated if there is air immediately beneath it, as with a pneumoperitoneum. Localized loss of clarity occurs when the diaphragm is not tangential to the X-ray beam, but usually indicates adjacent pulmonary or pleural disease, e.g. the costophrenic or costovertebral angles are obliterated by pleural fluid, and much of the diaphragmatic outline may be obliterated by basal pneumonia. Each hemidiaphragm is normally represented on the PA radiograph by a smooth, curved line which is convex upwards. The lateral attachment of the diaphragm to the ribs is represented by the lateral costophrenic recess, a sharply-defined acute angle. When the diaphragm is flat, as in emphysema, the most lateral muscle slips extend slightly upwards and may be seen as digitations. The costophrenic angle then becomes less acute, or even obtuse, and the appearance may simulate a small pleural effusion. Medially, the diaphragm meets the heart at the cardiophrenic angle. This is higher than the costophrenic angle and unlike the latter is often ill-defined owing to the presence of fat. On the right, this may simulate disease in the middle lobe, and on the left, disease in the lower lobe or lingula. Prominent fat pads at the cardiophrenic angles are an occasional cause of overestimation of the transverse cardiac diameter, particularly if the film is underexposed. On correctly exposed radiographs, the relatively low radio-opacity of the fat pad enables it to be distinguished from the cardiac apex. On the lateral radiograph each dome makes an acute angle with the ribs posteriorly to form the posterior costophrenic recesses. The latter lie considerably lower than the highest part of each leaf—a point of great importance, as localized pulmonary or pleural disease adjacent to the posterior aspect of the diaphragm will often not be recognized on the PA radiograph, on which only the highest anterior portion of the diaphragmatic dome is represented. The right hemidiaphragm makes an upward curve as it extends anteriorly to the sternum. This part of its attachment is often poorly defined because of adjacent fat. Localization of disease requires the correct identification of each leaf on the lateral radiographs. The left diaphragm is obscured anteriorly by the heart and usually has an air-distended gastric fundus beneath it; whichever leaf is nearer the film is related to the ribs least magnified by the diverging beam.

Height In most people the diaphragm in the mid lung field lies at the level of the fifth or sixth anterior rib interspace. It may lie at a lower level in normal young individuals, particularly those of an asthenic build and at a slightly higher level in the obese, the elderly and young infants. In over 90% of normal people the right hemidiaphragm is higher than the left. This difference in height on the PA film is usually about 15 mm, but may be as much as 30 mm. Depression of the diaphragm occurs in emphysema and in acute severe asthma, but flattening only occurs in emphysema.

Inversion of the diaphragm is sometimes seen with a tension pneumothorax and with large basal bullae. It is also a common accompaniment of pleural effusions.Table 13.3 shows the most common causes of bilateral symmetrical elevation of the diaphragm. Elevation of a single hemidiaphragm is usually secondary to adjacent pleural, pulmonary or subphrenic disease, or to phrenic nerve palsy (Table 13.4). A minor degree of diaphragmatic elevation is a common accompaniment of pleurisy, lower lobe pneumonia and pulmonary thromboembolism. In the latter there may be no visible change in the affected lung. Upper abdominal inflammatory processes and rib fractures may also cause a high diaphragm. A high hemidiaphragm may be mimicked by a subpulmonary pleural effusion (Fig. 13.20), a large well-defined tumour adjacent to the dome, or by combined middle and lower lobe collapse.

Eventration In eventration a part of the normal diaphragmatic muscle is replaced by a thin layer of connective tissue and a few scattered muscle fibres25. The unbroken continuity differentiates it

Table 13.3 CAUSES OF BILATERAL SYMMETRICAL ELEVATION OF THE DIAPHRAGM Supine position Poor inspiration Obesity Pregnancy Abdominal distension (ascites, intestinal obstruction, abdominal mass) Diffuse pulmonary fibrosis Lymphangitis carcinomatosa Disseminated lupus erythematosus Bilateral basal pulmonary emboli Painful conditions (after abdominal surgery) Bilateral diaphragmatic paralysis

Table 13.4 CAUSES OF UNILATERAL ELEVATION OF THE DIAPHRAGM Posture—lateral decubitus position (dependent side) Gaseous distension of stomach or colon Dorsal scoliosis Pulmonary hypoplasia Pulmonary collapse Phrenic nerve palsy Eventration Pneumonia or pleurisy Pulmonary thromboembolism Rib fracture and other painful conditions Subphrenic infection Subphrenic mass

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Figure 13.20 Subpulmonary pleural effusion. On the (A) erect PA and (B) lateral radiograph the effusion simulates a high hemidiaphragm. (C) Ultrasound and (D) CT clearly show that the effusion is located above the diaphragm. Arrows = diaphragmatic area.

from diaphragmatic hernia. Some authors consider eventration to be a congenital anomaly resulting from failure of muscularization of part or all of the diaphragmatic leaf. Most authors, however, also include within the definition elevation occurring as a result of acquired paralysis with atrophy of the diaphragmatic muscle; an inclusion justified by the fact that many adults with surgically proven eventration have previously had normal chest radiographs. Total eventration shows a marked left-sided predominance, for which there is no acceptable explanation. Although eventration is a recognized cause of respiratory distress in the newborn, it is not usually associated with symptoms in the adult. Localized forms of the condition are relatively common, particularly in the elderly, and predominantly affect the right hemidiaphragm at its anteromedial aspect (Fig. 13.21). The distinction between a localized eventration and a small diaphragmatic hernia or a mass arising from the lung,

pleura, or diaphragm is best made using CT or MRI. The various causes of focal elevation or bulging of a diaphragm are given in Table 13.5.

Movement and paralysis Unequal excursion of the two hemidiaphragms occurs in approximately 80% of normal people. However, this inequality of diaphragmatic excursion is less than 10 mm in most people. While normal young adults can move the diaphragm over at least 30 mm, this range is greatly reduced in the elderly. As the chest radiograph is exposed at the end of a full inspiration, any severe unilateral limitation of diaphragmatic movement will be apparent on this static examination. Diaphragmatic movement is, however, better assessed by fluoroscopy, which should, ideally, be performed in both the AP and lateral projections with the patient erect and supine. The

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Figure 13.21 Focal eventration. (A) PA chest radiograph reveals a soft tissue opacity arising from the diaphragm. (B) CT shows the presence of fat and liver under the elevated part of the diaphragm.

latter position is useful as the range of movement is usually greater than it is in the erect position. With the patient in the lateral position, any inequality of movement of the two leaves is readily assessed and localized restriction of movement identified better26. Restriction of diaphragmatic movement occurs secondary to disease of the phrenic nerve and secondary to inflammatory and painful conditions adjacent to the diaphragm, such as lower lobe pneumonia and subphrenic infection. Phrenic palsy is most commonly secondary to involvement of the phrenic nerve by tumour—usually a bronchial carcinoma. Phrenic nerve paresis may be caused by trauma (road accidents, birth injury, brachial plexus block and phrenic crush), irradiation and a variety of neurological conditions such as poliomyelitis, herpes zoster, and cervical disc degeneration. The recognition of phrenic paresis depends upon finding a high hemidiaphragm which exhibits absent, restricted, or paradoxical movement.The latter is particularly well demonstrated by sniffing. Diaphragmatic motion can also be examined with ultrasound26. Especially in patients who cannot come to the fluoroscopy room, bedside ultrasound is very useful. This technique has also a high accuracy to discover absent and paradoxical diaphragmatic

Table 13.5 CAUSES OF FOCAL ELEVATION (BULGE) OF THE DIAPHRAGM Partial eventration Diaphragmatic hernia Diaphragmatic tumour Pleural tumour Pulmonary tumour Focal diaphragmatic dysfunction Focal diaphragmatic adhesions

motion. In addition measurement of diaphragmatic thickness can be helpful to confirm diaphragmatic paralysis, since a paralysed diaphragm does not thicken during inspiration. An important mimic of phrenic paresis is eventration (usually left sided, see above). In a significant small number of patients in whom there is little doubt that a phrenic paresis exists, no cause can be discovered. In this ‘idiopathic’ group the right leaf is more commonly affected than the left and it has been suggested that the palsy may be a legacy of previous viral neuritis. Weakness or paralysis of both hemidiaphragms is most commonly seen in association with chronic neuromuscular disease and causes severe clinical disability. Bilateral paralysis may not be recognized by fluoroscopic examination, for passive descent of the diaphragm may occur with inspiration.

Diaphragmatic hernias Intrathoracic herniation of abdominal contents occurs through congenital defects in the muscle, through traumatic tears or, most commonly, through acquired areas of weakness at the central oesophageal hiatus. Congenital hernias presenting in childhood are discussed elsewhere. When the defect is small it may not come to attention until adulthood, when it usually presents as an incidental abnormality on the chest radiograph. Bochdalek defects through the pleuroperitoneal canal occur along the posterior aspect of the diaphragm and the hernia usually contains retroperitoneal fat or a portion of kidney or spleen27 (Fig. 13.22). The majority occur on the left. A well-defined, dome-shaped, soft tissue opacity is seen midway between the spine and lateral chest wall on the frontal view and above the posterior costophrenic recess on the lateral view. It may appear to ‘come and go’ on serial PA radiographs because of varying degrees of inspiration and differences in transdiaphragmatic pressure. It has been shown that asymptomatic small Bochdalek hernias are present in 6% of otherwise

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Figure 13.22 Bochdalek hernia. (A) Lateral chest radiograph shows a focal bulge on the diaphragmatic contour just above the posterior costophrenic recess (arrows). (B) CT shows a fatty mass abutting the defect in the posteromedial aspect of the left hemidiaphragm (arrowheads).

normal adults.These hernias appear on a lateral radiograph as a focal bulge centred approximately 4–5 cm anterior to the posterior diaphragmatic insertion. On CT and MRI the diagnosis can be made when a soft tissue or fatty mass is seen protruding through a small defect in the posteromedial aspect of either hemidiaphragm. A Morgagni hernia presents in adulthood as an anterior opacity at the right cardiophrenic angle. It frequently contains omentum and may contain gut. Its smooth, welldefined margin and soft tissue radiodensity usually allow its differentiation from the much more common fat pad collection at this site. It is more difficult to differentiate from a low-lying pericardial cyst. Morgagni hernias containing gut can be diagnosed using barium but the diagnosis is more simply established by means of CT or MRI. Hernias through the oesophageal hiatus are extremely common, particularly in the elderly in whom they may be an incidental finding on CT.

Diaphragmatic trauma Because diaphragmatic rupture is often associated with thoracic or abdominal injuries that require surgical treatment, many cases are diagnosed during surgery28. If surgery is not indicated, diaphragmatic tear can be missed, especially when it is small and when there is no herniation of abdominal structures to the chest. That is why suspicion is needed in all cases of trauma to the lower chest, but also in patients with severe pelvic trauma. The chest X-ray should be evaluated carefully. Special attention has to be given to small changes in the diaphragm or to basal lung atelectasis or consolidation. If possible, the post-traumatic thorax should always be compared with previous chest X-rays. The diagnostic tools are different in the acute and latent phase. In the acute phase surgical procedures are often necessary and if the patient has severe injuries bedside examinations, such as chest X-ray and ultrasound, should be relied upon (Fig. 13.23). In the latent phase barium studies, spiral CT and MRI can give additional diagnostic information.

Figure 13.23 Traumatic diaphragmatic rupture. (A) Ultrasound and (B) CT show traumatic laceration of the liver and herniation of liver tissue into the fluid-filled pleural space.

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In the acute phase the chest X-ray is normal in about onequarter of cases. In some cases gas and fluid shadows are seen in the thorax. Sometimes there is only a localized density in close relationship to the diaphragm, or an alteration in the diaphragmatic shape. The position of a nasogastric tube can help to localize the gastric fundus, but does not tell anything about the position of the diaphragm, which is essential in the diagnosis of a diaphragmatic tear. A follow-up X-ray of an acutely injured patient showing progressive opacification of one thorax side by a gas-filled structure is strongly suggestive for diaphragmatic rupture (Fig. 13.24). Barium studies can be very helpful in making the correct diagnosis, when an extrinsic narrowing occurs on the border of the stomach or bowel at the point where they pass the

• THE CHEST WALL, PLEURA, DIAPHRAGM AND INTERVENTION

diaphragmatic tear. However, since barium studies cannot be used in emergency situations, they are predominantly indicated in the latent phase and eventually in the obstructive phase. Pneumoperitoneum can be established by bringing a small amount of air into the abdominal cavity. If air shifts through the diaphragmatic tear and a pneumothorax occurs, the test is diagnostic for diaphragmatic rupture. However, no shift of air will occur when the tear is closed by adhesions or by the herniated organs themselves. In this case the exact position of the diaphragm can be visualized since it is delineated by the subdiaphragmatic air. Ultrasound can be diagnostic if both the diaphragm and the herniated organs can be visualized. Examination of the right hemidiaphragm is facilitated by the presence of the liver,

Figure 13.24 Traumatic rupture of the diaphragm diagnosed 2 months after the trauma. (A) Detail of the left hemithorax. The supine chest radiograph immediately after the trauma shows multiple rib fractures, a pleural effusion and a poorly-defined opacity at the left lung base. (B) One month after the trauma the chest radiograph is normal but (C) 2 months later a large gas-filled structure corresponding with the air-containing stomach is seen in the left hemithorax suggesting rupture and herniation. (D) CT confirmed the diagnosis of diaphragmatic rupture and shows the herniated stomach (S).

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Figure 13.25 Primary malignant tumour of the diaphragm. (A) PA chest radiograph shows a small focal bulge of the diaphragm in combination with a small pleural effusion. (B) CT and (C) MRI show an irregular mass with central necrosis in continuity with the right hemidiaphragm (arrows).

acting as an acoustic window. However, this technique is limited by the often minimal visualization of the diaphragm itself, the tenderness over the upper abdomen and the presence of gas in herniated bowel. The MDCT diagnosis of diaphragmatic rupture is largely based on the fact that abdominal organs are seen in the pleural space outside the diaphragm. However, the identification of the diaphragm on standard CT images can be very difficult; multiplanar CT reconstructions can help to show the defect directly. The more usual CT signs of diaphragmatic rupture include29,30: discontinuity of the diaphragm with direct visualization of the diaphragmatic injury; herniation of abdominal organs with liver, bowel or stomach in contact with the posterior ribs (‘dependent viscera sign’); thickening of the crus (‘thick crus sign’); constriction of the stomach or bowel (‘collar sign’); active arterial extravasation of contrast material near the diaphragm; and, in the case of a penetrating diaphragmatic injury, depiction of a missile or puncturing instrument trajectory. Because it is in most cases difficult to perform an MRI examination during the acute phase, this technique is more valuable in the latent phase. It allows both a static and a dynamic view of the diaphragm. However, as in CT, the parts of the diaphragm in contact with the liver and spleen are not visible.

Neoplasms of the diaphragm Primary tumours of the diaphragm are rare (Fig. 13.25). Both benign and malignant varieties are mostly derived from muscle, fibrous tissue, blood vessels, or fat. They are usually well defined and on the right may mimic an elevated diaphragm or local eventration. Calcification has been described in lipomas. Malignant tumours may present as a pleural effusion. Secondary invasion of the diaphragm by malignant tumours of the lung, pleura, stomach, or pancreas may occur. Imaging with CT or MRI is particularly helpful in such patients.

REFERENCES 1. Kuhlman J E, Bouchardy L, Fishman E K et al 1994 CT and MR imaging evaluation of chest wall disorders. RadioGraphics 14: 571–595 2. Fortier M, Mayo J R, Swensen S J et al 1994 MR imaging of the chest wall lesions. Radiographics 14: 597–606

3. Takasugi J E, Rapoport S, Shaw C 1989 Superior sulcus tumors: the role of imaging. J Thorac Imaging 4: 41–48 4. Deschildre F, Petyt L, Remy-Jardin M et al 1994 Evaluation de la TDM par balayage spirale volumique (BSV) vs IRM dans le bilan d’extension pariétal des masses thoraciques. Rev Im Med 6(S): 188 5. Müller N L 1993 Imaging the pleura. Radiology 186: 297 6. McLoud T C, Flower C D R 1991 Imaging the pleura: sonography CT, and MR imaging. Am J Roentgenol 156: 1145–1153. 7. Fleischner F G 1963 Atypical arrangement of free pleural effusion. Radiol Clin North Am 1: 347–362 8. Lomas D J, Padley S G, Flower C D R 1993 The sonographic appearances of pleural fluid. Br J Radiol 66: 619–624 9. McLoud T C 1998 CT and MR in pleural disease. Clin Chest Med 19: 261–276 10. Bittner R C, Schnoy N, Schonfeld N et al 1995 High-resolution magnetic resonance tomography (HR-MRT) of the pleura and thoracic wall: normal findings and pathological changes. Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 162: 296–303 11. Lesur O, Delorme N, Fromaget J M et al 1990 Computed tomography in the etiologic assessment of idiopathic spontaneous pneumothorax. Chest 98: 341–347 12. Gordon R 1980 The deep sulcus sign. Radiology 136: 25–27 13. Rhea J T, vanSonnenberg E, McLoud T C 1979 Basilar pneumothorax in the supine adult. Radiology 133: 593–595 14. Aberle D R, Gamsu G, Ray C S 1988 High resolution CT of benign asbestos-related diseases: clinical and radiographic correlation. Am J Roentgenol 151: 883 15. Falaschi F, Battolla L, Maschalchi M et al 1996 Usefulness of MR signal intensity in distinguishing benign from malignant pleural disease. Am J Roentgenol 166: 963–968 16. England D M, Hochholzer L, McCarthy M J 1989 Localized benign and malignant fibrous tumors of the pleura. A clinicopathologic review of 223 cases. Am J Surg Pathol 13: 640–658 17. Kinoshita T, Ishii K, Miyasato S 1997 Localized pleural mesothelioma: CT and MR findings. Magn Reson Imaging 15: 377–379 18. Layer G, Schmitteckert H, Steudel A et al 1999 MRT, CT and sonography in the preoperative assessment of the primary tumor spread in malignant pleural mesothelioma. RoFo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 170: 365–370 19. Rusch V W, Godwin J D, Shuman W P 1988 The role of computed tomography scanning in the initial assessment and the follow-up of malignant pleural mesothelioma. J Thorac Cardiovasc Surg 96: 171 20. Klein J S, Zarka M 1997 Transthoracic needle biopsy: an overview. J Thorac Imaging 12: 232–249 21. vanSonnenberg E, Casola G, Ho M et al 1988 Difficult thoracic lesions: CT-guided biopsy experience in 150 cases. Radiology 167: 457–461 22. Ikezoe J, Morimoto S, Kozuka T 1991 Sonographically guided needle biopsy of thoracic lesions. Semin Intervent Radiol 8: 15–22

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23. White C S, Meyer C A, Templeton P A 2000 CT fluoroscopy for thoracic interventional procedures. Radiol Clin North Am 38: 303–322 24. Buecker A, Adam G, Neuerburg J M et al 1998 MR-guided biopsy using a T2-weighted single-shot zoom imaging sequence (local look technique). J Magn Reson Imaging 8: 955–959 25. Deslauriers J 1988 Eventration of the diaphragm. Chest Surg Clin North Am 8: 315–330 26. Houston J G, Fleet M, Cowan M D et al 1995 Comparison of ultrasound with fluoroscopy in the assessment of suspected hemidiaphragmatic movement abnormality. Clin Radiol 50: 95–98

• THE CHEST WALL, PLEURA, DIAPHRAGM AND INTERVENTION

27. Demartini W J, House A J S 1980 Partial Bochdalek herniation: computerized tomographic evaluation. Chest 77: 702–704 28. Shah R, Sabanathan S, Mearns J A et al 1995 Traumatic rupture of diaphragm. Ann Thorac Surg 60: 1444–1449 29. Bergin D, Ennis R, Keogh C et al 2001 The “dependent viscera” sign in CT diagnosis of blunt traumatic diaphragmatic rupture. Am J Roentgenol 177: 1137–1140 30. Leung J C, Nance M L, Schwab C W et al 1999 Thickening of the diaphragm: a new computed tomography sign of diaphragm injury. J Thorac Imaging 14: 126–129

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CHAPTER

The Mediastinum, Including the Pericardium*

14

Sharyn L. S. MacDonald and Simon Padley

Mediastinal diseases • Mediastinal masses • Other mediastinal lesions The pericardium • Normal anatomy

• Imaging pericardial disease • Developmental anomalies • Acquired pericardial disease

MEDIASTINAL DISEASES MEDIASTINAL MASSES Incidence The true incidence of mediastinal masses is difficult to ascertain because most surgical series are biased towards patients requiring surgery and therefore do not include all aneurysms, intrathoracic goitres, or lymph node masses in patients with established diagnoses such as lymphoma or sarcoidosis. In adult surgical series1–3, the most frequent tumours are of neurogenic (17–23%) or thymic (20–25%) origin, or are neoplastic disorders of lymph nodes (10–20%). Developmental cysts, thyroid masses, and germ-cell tumours constitute the next most frequent group (approximately 10% each). In children, neuroblastoma/ganglioneuroma, foregut cysts and germ-cell tumours account for over three-quarters of cases, whereas thymoma and thyroid masses are rare. Mediastinal masses are conventionally divided by location into anterior, middle, or posterior mediastinal compartments. This division into compartments is for descriptive convenience only, since it is not based on anatomical boundaries that limit spread; nor do radiologists in general use these terms in the way they are defined by anatomists. Localization of a mass to one of these compartments is a useful step towards reaching the most appropriate diagnosis or differential diagnosis; the age of the patient and such characteristics as the presence of calcification, fat, fluid, or soft tissue within the mass, invasion of the mediastinal fat (indicating malignant rather that

benign disease) and contrast enhancement characteristics on computed tomography (CT) and magnetic resonance imaging (MRI) are important in narrowing the differential diagnosis, which is considered later in this chapter.

Imaging techniques Mediastinal masses are often incidentally detected on chest radiograph. Despite diagnostic limitations the chest radiograph is also important for detecting and localizing mediastinal masses when suspected clinically.

Computed tomography Computed tomography is the most useful investigation for localizing, characterizing and demonstrating the extent of a mediastinal mass and its relationship to adjacent structures. Multidetector CT (MDCT) following intravenous contrast medium with multiplanar reformats provides an excellent assessment of mediastinal structures, including vessels, and has largely obviated the need to proceed to MRI for imaging in the coronal and sagittal planes. CT may also be used to guide biopsy, plan resection and follow response to therapy.

Magnetic resonance imaging Magnetic resonance imaging remains useful for imaging suspected neurogenic tumours, for demonstrating intraspinal extension of a mediastinal mass and for further evaluating the relationship of a mass to the heart, pericardium and larger intrathoracic vessels. MRI may have advantages over

*The section on the pericardium is adapted from Chapter 42 by Anna Rozenshtein, Lawrence M. Boxt, Kathleen Reagan and Robert M. Steiner from the fourth edition of this textbook.

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contrast-enhanced CT for distinguishing between solid tissue and adjacent vessels (fast flowing blood in vessels results in a signal void on spin-echo sequences) and may be useful for confirming that a mass is cystic. Unlike CT, MRI is not sensitive to the presence of calcification.

Ultrasound Ultrasound of the mediastinum, including echocardiography and endoscopic ultrasound, may be of use in selected patients, in particular for distinguishing cystic from solid mediastinal masses and for distinguishing cardiac from paracardiac masses. Ultrasound may also be used to guide mediastinal biopsy.

Radionuclide examinations Radionuclide examinations have a limited role in the assessment of mediastinal masses. Positron emission tomography (PET) and PET–CT using [F-18]2-deoxy-d-glucose (18F-FDG) has proven useful in the evaluation of mediastinal lymph node involvement in lung cancer and lymphoma4,5. Radionuclide examinations may also be useful in the imaging of thyroid masses, neuroendocrine tumours and phaechromocytomas.

Thyroid masses Most thyroid masses (Fig. 14.1) in the mediastinum represent downward extensions of either a multinodular colloid goitre or, occasionally, an adenoma or carcinoma. Intrathoracic thyroid masses usually have a well-defined outline, which may be spherical or lobular. Rounded or irregular, well-defined areas of calcification may be seen in benign areas, whereas amorphous cloud-like calcification is occasionally seen within carcinomas. Almost all intrathoracic thyroid masses displace the trachea, which may also be substantially narrowed. The direction of displacement depends on the location of the mass. Thyroid

masses are most commonly anterior and lateral to the trachea. Posteriorly placed masses often separate the trachea and the oesophagus, and such separation by a localized mass rising into the neck is virtually diagnostic of a thyroid mass. Radionuclide imaging with 123I or 131I demonstrates the presence of thyroid tissue within the mediastinum in almost all intrathoracic goitres. Although radionuclide imaging is a sensitive and specific method of determining the thyroid nature of an intrathoracic mass, CT is more useful as the initial investigation because it provides more information should the mass prove to be something other than a thyroid lesion and is almost as specific as nuclear medicine in diagnosing a thyroid origin. CT optimally demonstrates the shape, size and position of the mass (Fig. 14.2)6,7. It is usually possible to diagnose a thyroid origin by noting a well-defined mass in the paratracheal or retrotracheal region, almost invariably being continuous with the thyroid gland in the neck. Another useful sign is that normal thyroid tissue within the mass shows a higher attenuation value than muscle on images obtained both before and after contrast medium. Focal areas of calcification are frequently identified and rounded, focal, nonenhancing low density areas are common. It is not possible to distinguish between a benign and malignant mass on CT unless the tumour has clearly spread beyond the thyroid gland. It should, however, be noted that multiple masses are a feature of benign multinodular goitre, though carcinoma can develop in multinodular goitre. MRI of intrathoracic goitre, like CT, can identify cystic and solid components, and can show haemorrhage to advantage, but will not reliably demonstrate calcification.

Parathyroid masses The parathyroid glands may migrate into the chest during fetal development. Mediastinal parathyroid tumours causing hyperparathyroidism are most commonly located in or around

Figure 14.1 Intrathoracic thyroid mass on (A) AP and (B) lateral radiographs. This benign multinodular goitre is predominantly posterior to the trachea with components to either side, resulting in forward displacement and narrowing of the trachea.

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otherwise normal gland, may lie within a thymoma, or may follow thymic irradiation for Hodgkin’s disease10.

Thymomas

Figure 14.2 Intrathoracic extension of thyroid on coronal image from multidetector CT. Contrast medium has been administered. The thyroid demonstrates heterogeneous contrast enhancement, and is mainly of greater attenuation than skeletal muscle. There are flecks of calcification in the gland.

the thymus. They are small and almost never visible on plain radiographs. They are probably best detected using ultrasound (Fig. 14.3) and if not readily apparent, by subsequent 99m Tc-sestamibi imaging with CT or MRI only in selected cases8,9.

Thymic tumours Tumours that arise within the thymus include thymoma, lymphoma, thymic carcinoid, germ-cell tumour/teratoma and thymolipoma. Thymic cysts are another cause of a thymic mass (Fig. 14.4). They may be simple cysts and occur in an

Figure 14.3 High-resolution ultrasound of the left lobe of the thyroid (LLT) anterior to a parathyroid adenoma (white arrows). There is a small area of cystic degeneration within the posterior aspect of the adenoma. Black arrows indicate the common carotid artery.

Thymomas are the most common tumour of the thymus in adults, and the most common primary tumour of the anterior mediastinum in adults. The average age at diagnosis is approximately 50 years, earlier in those who present with myasthenia gravis. Thymomas are rare under 20 years of age and extremely unusual below the age of 15. Up to 50% of patients with thymoma have myasthenia gravis, and approximately 10–20% of patients with myasthenia gravis have a thymoma. A variety of other syndromes are seen in patients with thymoma, including hypogammaglobulinaemia and red cell aplasia11,12. Most thymomas (90%) arise in the upper anterior mediastinum. The mass is usually anterior to the ascending aorta, lying above the right ventricular outflow tract and pulmonary artery (Fig. 14.5). A few are situated more inferiorly, projecting from the left or right heart border, or lying close to the cardiophrenic angles. They are usually spherical or oval in shape and may show lobulated borders. They may contain one or more cysts and a few are predominantly cystic (Fig. 14.6). Calcification, punctate or curvilinear, may be seen (Fig. 14.7). All of these features are best demonstrated using CT13,14, which is the most sensitive technique for the detection of thymoma in patients with myasthenia gravis15. The diagnosis depends on identifying a focal swelling rather than applying a specific measurement. Thymomas as small as 1.5– 2.0 cm in diameter are readily identified over the age of 40, largely because the rest of the thymus is atropic. Before age 40, and particularly before 30, diagnosing a small thymoma can be difficult, because the normal gland is variable in size and in myasthenia gravis the associated hyperplasia may cause a bulky gland. In these circumstances a useful rule is that thymoma usually gives rise to an asymmetrical focal swelling. Fortunately, thymoma is so infrequent in children that the potentially difficult problem of finding a thymoma in a child with myasthenia gravis rarely arises. Thymomas usually show homogeneous density and uniform enhancement after contrast medium and may occasionally be cystic. Invasion of the mediastinal fat and adjacent pleura may be identified with invasive thymomas (Fig. 14.8), and while CT shows such invasion to advantage it cannot reliably diagnose invasive thymoma if the tumour is still confined to the thymus16. Remote pleural metastases resulting from transpleural spread are a feature of invasive thymomas, and therefore the whole of the pleural cavity should be carefully examined16 (Fig. 14.8). MRI, in general, provides similar information to CT, though it can be useful to show mediastinal spread when there is doubt on the latter. On T1-weighted images, thymomas have a signal intensity similar to that of muscle and the adjacent normal thymic tissue. On T2-weighted images, the signal intensity increases and may make it difficult to distinguish a thymoma from adjacent mediastinal fat. Heterogeneity of signal intensity caused by septation, cystic change and haemorrhage is common16.

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Figure 14.4 Thymic cyst producing an anterior mediastinal mass on (A) AP and (B) lateral chest radiographs, filling in the normal retrosternal window and widening the mediastinum. (C) The cystic nature is best demonstrated by CT.

Figure 14.5 Thymic enlargement on (A) PA and (B) lateral radiographs of a patient with a malignant thymic mass. The lateral view demonstrates pleural metastases posteriorly (arrows). (C) CT confirms the anterior position of the primary tumour suspected from the filling of the retrosternal window apparent on the lateral radiograph (B).

Thymic carcinomas Thymic carcinomas are aggressive locally invasive malignancies that have frequently metastasized to regional lymph nodes and distant sites at presentation. They are typically large, heterogeneous masses, containing areas of necrosis and calcification and demonstrating evidence of invasion of adjacent structures, in particular the mediastinum, pericardium and pleura17,18.

Thymic lymphoma Thymic lymphoma is usually part of generalized disease, but isolated involvement is very occasionally encountered. It is most commonly associated with Hodgkin’s disease. The imaging features are the same as those of thymoma. Figure 14.6 Cyst formation in a thymoma demonstrated on CT in a patient with myasthenia gravis. The wall is irregular and enhances following administration of intravenous contrast medium.

Thymic carcinoid Thymic carcinoid is histologically distinct from thymoma. A noteworthy feature is that these tumours may secrete

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Figure 14.7 Thymoma presenting on a chest radiograph obtained before orthopaedic surgery in an otherwise asymptomatic elderly female patient. There is a large anterior mediastinal mass (A) with coarse calcification visible on (B) the lateral view and (C) contrast-enhanced CT.

Figure 14.8 Invasive thymoma in a young man. (A) Shows a lobular anterior mediastinal mass associated with a pleural effusion. (B) Image obtained through the lower chest demonstrates mixed soft tissue (arrows) and fluid attenuation owing to transpleural spread of tumour.

adrenocorticotropic hormones in sufficient quantities for the patient to present with Cushing’s syndrome. The plain radiograph and CT features of thymic carcinoid are indistinguishable from those of thymoma.

Thymolipomas Thymolipomas are rare tumours composed of a mixture of mature fat and normal-looking or involuted thymic tissue.The age range is 3–60 years. Individual cases have been reported in association with a variety of conditions, including myasthenia gravis, aplastic anaemia, Graves’ disease and hypogammaglobulinaemia. Thymolipomas can grow to a very large size before discovery and, being soft, mould themselves to the adjacent mediastinum and diaphragm, and may mimic cardiomegaly or lobar collapse19. CT/MRI show the fatty nature of the mass, with islands of thymus and fibrous septa running through the lesion19,20.

Thymic hyperplasia The most common association of thymic hyperplasia is myasthenia gravis, but thymic hyperplasia is also seen in other conditions, notably thyrotoxicosis. Thymic hyperplasia is rarely severe enough to cause visible enlargement of the thymus, but when it does, both lobes are enlarged, usually uniformly, though on occasion thymic hyperplasia may mimic a thymic mass. The thymus may atrophy due to stress or as a consequence of steroid or antineoplastic drug therapy21,22.The gland usually returns to its original size on recovery or cessation of treatment, but it may become larger than its previous normal size in the phenomenon known as rebound thymic hyperplasia. It may then be difficult to distinguish between thymic rebound and thymic involvement by neoplasm. The diagnosis depends on a known reason for thymic rebound, the absence of clinical

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features to indicate tumour recurrence and the presence of an enlarged, normally-shaped thymus22,23.

Germ-cell tumours of the mediastinum Germ-cell tumours of the mediastinum are believed to be derived from primitive germ-cell elements left behind after embryonal cell migration. The mediastinum is the most common extragonadal site for these tumours, almost all of which arise in the anterior mediastinum, within, or in intimate contact with, the thymus. Mediastinal germ-cell tumours include mature teratoma (benign) and a number of malignant forms, chiefly seminoma, malignant teratoma, embryonal carcinoma, choriocarcinoma, endodermal sinus tumour and tumours with mixtures of these cell types24. Malignant germ-cell tumours secrete human chorionic gonadotrophin and α-fetoprotein, which can be used as markers to diagnose and monitor the tumour.

Mature teratomas Mature teratomas are the most common mediastinal germcell tumour2; most are cystic. Mature teratomas are found at all ages, particularly in adolescents and young adults, with women slightly outnumbering men25,26. They are usually asymptomatic and diagnosed incidentally on chest radiography or CT, but may give rise to cough, dyspnoea, or chest pain if they compress the bronchial tree or superior vena cava, or if they rupture into the mediastinum or lung. They are frequently large and may be huge, occupying much of one hemithorax. The lesions are usually stable, but haemorrhage or infection may lead to a rapid increase in size. On chest radiograph or CT most mature teratomas present as a well-defined, rounded or lobulated mass, localized to the anterior mediastinum. Fat and calcification may occasionally be identified on chest radiograph. CT appearances are variable, combinations of fat, fluid, soft tissue components and calcification may be seen25 (Fig. 14.9). The presence of fat, either as focal collections or fluid fat, is a very helpful diagnostic feature

favouring mature (benign) cystic teratoma over the other causes of anterior mediastinal mass. MRI provides similar information to CT, although it may not detect calcification.

Malignant germ-cell tumours Malignant germ-cell tumours are usually seen in young adults and are much more common in men (>90%) than women. Seminoma is the most common form27. They are more commonly more symptomatic than mature teratoma, usually due to mass effect or invasion of adjacent structures. The plain radiographic findings are similar except that the malignant tumours are more often lobular in outline, fat density is not seen and visible calcification is rare. Because they are malignant tumours, they grow rapidly and metastasize readily to the lungs, bones, or pleura. CT shows a lobular, asymmetrical mass.The adjacent mediastinal fat planes may be obliterated, and the tumours are either of homogeneous soft tissue density or show multiple areas of contrast enhancement interspersed with rounded areas of decreased attenuation due to necrosis and haemorrhage28,29. MRI provides similar information to CT (Fig. 14.10).

Mediastinal lymphadenopathy Lymph node calcification Extensive lymph node calcification is common following tuberculosis and fungal infection, and is occasionally seen with other infections. It may also be encountered in a variety of other conditions, notably sarcoidosis, silicosis and amyloidosis. Although it may be seen in lymph node metastases from calcifying primary malignancies, such as osteosarcoma, chondrosarcoma and mucinous colorectal and ovarian tumours, lymph node calcification is rare in metastatic neoplasm. It is virtually unknown in untreated lymphoma though it is occasionally seen in nodes involved by Hodgkin’s disease following therapy. CT demonstrates more calcification than plain radiographic techniques. Calcification is not usually visible on MRI. Two

Figure 14.9 Teratoma in a young man undergoing an immigration chest radiograph. (A) There are no specific features on the plain radiograph to indicate the nature of the mass. (B) CT demonstrates that the opacity visible on the chest radiograph is well defined and contains soft tissue and fat densities.

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with inflammatory disorders, particularly tuberculosis, fungal disease32, sarcoidosis and neoplasm. When striking, it points particularly to the diagnosis of metastatic neoplasm from a highly vascular primary tumour, such as melanoma, renal and thyroid carcinoma, carcinoid tumour, or leiomyoma/sarcoma. A rare cause of strikingly uniform contrast enhancement is Castleman’s disease. A low-density centre with rim enhancement of the enlarged node is a useful pointer towards the diagnosis of tuberculous infection31 (Fig. 14.12).

Lymph node enlargement Figure 14.10 Malignant germ-cell tumour in a 25 year old man presenting with chest pain, dyspnoea, malaise and features of pericardial tamponade. The CT shows a lobular asymmetrical mass with low attenuation areas corresponding to necrotic tumour intersected by neoplastic septation.

common patterns of calcification are coarse, irregularly-distributed clumps within the node and homogeneous calcification of the whole node. A strikingly foamy appearance is seen with Pneumocystis jiroveci (previously P. carinii) infection in acquired deficiency syndrome (AIDS) patients30 and in some cases of metastatic mucinous neoplasms. Sometimes there is a ring of calcification at the periphery of the node—so-called ‘eggshell calcification’, which is a particular feature of sarcoidosis and of prolonged dust exposure in coal and metal mines.

Low attenuation nodes On CT, areas of low attenuation within enlarged nodes, corresponding to necrosis (Fig. 14.11), may be seen in a variety of conditions, particularly tuberculosis31 and occasionally in fungal disease32, infections in immunocompromised patients, metastatic neoplasm (notably from testicular tumours33) and lymphoma34. Attenuation values below that of water are seen in fatty replacement of inflammatory nodes and have also been described in Whipple’s disease35.

When mediastinal or hilar nodes are greater than 2 cm in their short axis diameter, the enlargement is likely to be due to metastatic carcinoma, malignant lymphoma, sarcoidosis, tuberculosis, or fungal infection. With lesser degrees of enlargement the differential diagnosis broadens to include lymph node hyperplasia and pneumoconiosis. Widespread moderate mediastinal lymph node enlargement is a frequent accompaniment of chronic diffuse lung disease and bronchiectasis. Normal sized nodes are demonstrable at CT/MRI, but are not visible on plain chest radiographs or on conventional tomography. The ease with which enlarged nodes can be recognized using plain radiography varies according to their location. Nodes in the right paratracheal group are readily identified: they show uniform or lobular widening of the right paratracheal stripe. Enlarged azygos nodes displace the azygos vein laterally and enlarge the shadow that normally represents just the azygos vein to over 10 mm in its short axis diameter. If the lymph nodes beneath the aortic arch become large enough to project beyond the aortopulmonary window they cause a local bulge in the angle between the aortic arch and the main pulmonary artery. Hilar lymph node enlargement causes enlargement and/or lobulation of the outline of the hilar shadows (Fig. 14.13).The diagnosis of lymph node enlargement on

Contrast-enhanced CT Contrast enhancement of enlarged nodes, when moderate in degree, is non-specific, being seen

Figure 14.11 Low attenuation lymph node enlargement. There is necrosis within malignant right hilar and subcarinal nodes which have arisen from the primary tumour in the right lung.

Figure 14.12 Tuberculous lymphadenopathy. Following contrast enhancement there is rim enhancement and central low attenuation due to caseation (arrows).

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normally concave toward the lung, flattens or becomes convex towards the lung, an appearance that may be confused with left atrial enlargement. Posterior mediastinal lymph node enlargement causes localized displacement of the paraspinal and paraoesophageal lines. Lymph nodes elsewhere in the mediastinum are only recognizable on plain radiographs when substantially enlarged (Fig.14.14). CT is an excellent method for detecting mediastinal lymph node enlargement (Figs 14.15–14.17). It is usually easy to distinguish between the normal vascular structures and enlarged lymph nodes using contrast-enhanced CT, although without excellent opacification of the left atrium it may, on occasion, be difficult to distinguish enlarged subcarinal lymph nodes from a normal or enlarged left atrium. The short axis measurement provides the most representative guide to true size, since long axis measurements vary to a significant degree according to the orientation of the lymph node within the CT section. In the assessment of lymph node enlargement, MRI provides essentially the same information as CT, although its use is limited to selected cases due to longer acquisition times and relatively limited spatial resolution (which may make measurement of individual nodes difficult). Figure 14.13 Sarcoidosis producing symmetrical bilateral hilar lymph node enlargement.

plain radiography depends on the recognition of the edge of a round or oval hilar mass, an analysis that requires a detailed understanding of the normal anatomy of the hilar blood vessels. Subcarinal lymph node enlargement widens the carinal angle and displaces the azygo-oesophageal line, so that the subcarinal portion of the azygo-oesophageal line, which is

Sarcoidosis Sarcoidosis is the most common cause of intrathoracic lymph node enlargement, the hilar nodes being enlarged in almost all cases36. Additionally, tracheobronchial, aortopulmonary and subcarinal nodes are enlarged in over half the patients37. Anterior mediastinal nodes occasionally increase in size, but posterior mediastinal node enlargement is very unusual and it is seldom that either is seen in isolation. The important diagnostic feature of lymphadenopathy in sarcoidosis is its symmetry (Fig. 14.13).

Figure 14.14 Massively enlarged lymph nodes. (A,B) Massive anterior mediastinal lymphadenopathy due to malignant lymphoma. There are huge lobulated swellings in the upper anterior mediastinum which are easily seen in both projections. (C) Massive anterior mediastinal nodal enlargement secondary to Hodgkin’s disease demonstrated by CT. There is marked compression and distortion of the mediastinal structures and bilateral small pleural fluid reactions.

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Malignant lymphoma and leukaemia

Figure 14.15 Right paratracheal lymph node enlargement (arrows) due to sarcoidosis.

Malignant lymphoma often involves mediastinal and hilar lymph nodes, multiple nodal groups usually being involved, particularly in Hodgkin’s disease. Lymph node enlargement is seen in a higher proportion of patients with Hodgkin’s than non-Hodgkin’s lymphoma. Any intrathoracic nodal group may be enlarged and the possible combinations are legion, but the following generalizations regarding plain radiograph, CT and MRI findings can be made38,39. 1 The anterior mediastinal and paratracheal nodes are the groups most frequently involved, the tracheobronchial and subcarinal nodes also being enlarged in many cases. In most cases, the lymphadenopathy is bilateral but asymmetrical. Hodgkin’s disease, particularly the nodular sclerosing form, has a propensity to involve the anterior mediastinal and paratracheal nodes (Fig. 14.14). 2 Hilar node enlargement is rare without accompanying mediastinal node enlargement, particularly in Hodgkin’s disease. 3 The posterior mediastinal nodes are infrequently involved— the enlarged nodes are often low down in the mediastinum and contiguous retroperitoneal disease is likely. 4 The paracardiac nodes are rarely involved but become important as sites of recurrent disease because they may not be included in the initial radiation therapy fields40.

Lymph node enlargement is also seen occasionally with leukaemia, the pattern being the same as with lymphoma. The lymph node enlargement in both lymphoma and leukaemia may resolve remarkably rapidly with therapy (Fig. 14.18).

Figure 14.16 Malignant mediastinal lymph node enlargement due to metastases from a small cell carcinoma of the lung.

Tuberculosis and histoplasmosis Lymph node enlargement due to tuberculous or fungal infection may affect any of the nodal groups in the hila or mediastinum. One or more lymph nodes may be visibly enlarged and an associated area of pulmonary consolidation may or may not be present. Occasionally, widespread massive mediastinal and hilar node enlargement is seen. With healing, the nodes usually become smaller, often returning to normal size. Dense calcification is frequent both in nodes that stay enlarged and in those that shrink. The enlarged nodes, together with surrounding fibrosis, may compress the superior vena cava or pulmonary veins and cause obstruction. Rim enhancement with a low density centre may be seen with tuberculosis on contrast-enhanced CT examination31 (see Fig. 14.12). Metastatic carcinoma Mediastinal lymph node metastases from bronchial carcinoma are discussed in Chapter 18. Metastases may also occur from extrathoracic primary carcinomas. In one large series, half the cases of mediastinal lymph node enlargement from extrathoracic primary carcinomas arose from tumours of the genitourinary tract, particularly the kidney and testis41. Other major sources are head and neck tumours and breast carcinomas.

Figure 14.17 Metastatic malignant teratoma involving mediastinal nodes and directly invading the lumen of the superior vena cava (arrow), where it is outlined by intravenous contrast medium.

Reactive hyperplasia in nodes draining infection or neoplasm may cause mild nodal enlargement that is recognizable on CT but rarely so with plain radiograph techniques. Castleman’s disease is a specific type of lymph node hyperplasia of uncertain aetiology which can cause substantial lymph node enlargement

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Figure 14.18 (A,B) Acute lymphocytic leukaemia in a 9-year-old boy showing rapid resolution of massive mediastinal adenopathy following chemotherapy. The two radiographs were taken 7 d apart.

in many sites in the body. When seen within the thorax, the enlarged nodes are usually situated in the middle or posterior mediastinum. The lymph node mass is often localized to one area, can be huge, and may be very vascular. The nodes may calcify and may show striking contrast enhancement on both CT and MRI42,43.

Foregut duplication cysts ‘Foregut duplication cyst’ is a useful term that covers various congenital cysts derived from the embryological foregut, including bronchogenic, enteric and neurenteric cysts.

Bronchogenic cysts Bronchogenic cysts are usually solitary asymptomatic mediastinal masses which may present at any age. Typically they have

a thin fibrous capsule, are lined with respiratory epithelium and contain cartilage.The cyst contents usually consist of thick mucoid material. Most are located adjacent to the trachea or main bronchi44. The cysts can grow very large without causing symptoms, but they may compress surrounding structures, particularly the airways and give rise to symptoms. In rare cases they become infected or haemorrhage occurs into the cyst; these complications may be life-threatening, particularly in infants and young children. On chest radiography nonmalignant mediastinal cysts present as spherical or oval masses with smooth outlines projecting from either side of the mediastinum (Fig. 14.19). Most are unilocular and do not have a lobulated outline, though lobulation may be seen. They usually contact the carina or

Figure 14.19 Oesophageal duplication cyst on (A) chest radiography and (B) CT. This case shows the typical features of a well-defined spherical mass projecting from the mediastinum.

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main bronchi, but may be seen anywhere along the course of the trachea and larger airways, and frequently project into the middle and/or posterior mediastinum. Calcification of the wall or of the cyst contents is rare. When located in the subcarinal area, these cysts may closely resemble an enlarged left atrium. Foregut duplication cysts frequently push the carina forward and the oesophagus backward—displacements that are almost never seen with other masses (the exceptions being thyroid masses and an aberrant left pulmonary artery). CT is an excellent method of demonstrating the size, shape and position of a bronchogenic cyst (Fig. 14.20). In some cases, it may demonstrate a thin-walled mass, with contents of uniform CT attenuation close to that of water (0 HU), thereby effectively making the diagnosis of a fluid-filled cyst45. In other cases, the CT attenuation is similar to soft tissue and therefore to tumour, in which case the differential diagnosis becomes wider (Fig. 14.20). Rarely, the cyst may show uniformly high density, probably due to a high protein content, or very high density indicating a very high calcium content (milk of calcium) within the fluid46. MRI shows the expected features of a fluid-filled cyst.

Oesophageal duplication cysts Oesophageal duplication cysts are uncommon44. They usually present first in childhood, but may not present until adulthood: initial presentation up to the age of 61 has been reported. They are distinguished from bronchogenic cysts pathologically by the presence of smooth muscle in the walls and contain mucosa resembling that of the oesophagus, stomach, or small intestine. Many are clinically silent and are first discovered as an asymptomatic mass on an imaging examination of the chest, but they may cause dysphagia, pain, or other symptoms due to the compression of adjacent structures. A duplication cyst may become infected or ectopic gastric mucosa within the cyst may cause haemorrhage or perforation. The imaging features of oesophageal duplication cysts

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(see Fig. 14.19) on CT and MRI are identical to those of bronchogenic cysts (see Fig. 14.20) except that in the former the wall of the lesion may be thicker, the mass may assume a more tubular shape, and it may be in more intimate contact with the oesophagus44. Due to their close proximity to the oesophageal wall, barium swallow will show the features of extrinsic or intramural compression.

Neurenteric cysts Neurenteric cysts result from incomplete separation of the foregut from the notochord in early embryonic life. The cyst wall contains both gastrointestinal and neural elements with an enteric epithelial lining. There is usually a fibrous connection to the spine or an intraspinal component. Communication with the subarachnoid space or the gastrointestinal tract may be present, but communication with the oesophageal lumen is rare. There are typically associated vertebral body anomalies such as butterfly or hemivertebra. These cysts frequently produce pain and are often found early in life. Radiologically44, a neurenteric cyst is a well-defined, round, oval or lobulated mass in the posterior mediastinum between the oesophagus (which is usually displaced) and the spine. Appearances on CT and MRI are similar to those of other foregut duplication cysts, with MRI being the investigation of choice for demonstrating the extent of intraspinal involvement44.

Mediastinal pancreatic pseudocyst On rare occasions, a pancreatic pseudocyst extends into the mediastinum. Most patients are adults and have the clinical features of chronic pancreatitis; in children, the usual cause of the pseudocyst is trauma. On imaging examinations, most patients have left-sided or bilateral pleural effusions. The mediastinal component of the pseudocyst is almost always in the posterior mediastinum adjacent to the oesophagus, having gained access to the chest via the oesophageal or aortic hiatus47. CT is the optimal method of demonstrating these

Figure 14.20 Bronchogenic cyst. (A) Bronchogenic cyst in right paratracheal area in a young asymptomatic man. (B) In this instance the CT attenuation was almost the same as that of the other soft tissue structures and it was not possible to predict the cystic nature of the mass. The cyst was surgically removed.

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thin-walled cysts, which show continuity with the pancreas and any peripancreatic fluid collections.

Neurogenic tumours Neurogenic tumours are the most common tumours to arise in the posterior mediastinum, and most neurogenic tumours occur in this location44. Most neurogenic tumours in adults are benign and are discovered as asymptomatic masses on chest radiography, though some, particularly the malignant lesions, cause chest pain.They can be classified as tumours arising from peripheral nerves, including neurofibroma, neurilemmoma (schwannoma) and malignant tumours of nerve sheath origin (neurogenic sarcomas), or as tumours arising from sympathetic ganglia. MRI is the best investigation for these tumours48.

Peripheral nerve tumours Peripheral nerve tumours typically originate in an intercostal nerve in the paravertebral region. Radiologically, the benign tumours (neurofibromas and schwannomas) present as welldefined round or oval posterior mediastinal masses. Pressure deformity causing a smooth, scalloped indentation on the adjacent ribs, vertebral bodies, pedicles, or transverse processes is common, particularly with the larger lesions44,49 (Fig. 14.21). The scalloped cortex is usually preserved and is often thickened.These bone changes are diagnostic of a neurogenic lesion, the only differential diagnosis being that of a lateral thoracic meningocele. The rib spaces and the intervertebral foramina may be widened by the tumour44,49. On CT the tumours may be homogeneous or heterogeneous, usually enhancing heterogeneously after intravenous contrast medium50. Punctate foci of calcification may be seen. On MRI neurofibroma and neurilemmoma have variable T1-weighted signal intensity that may be similar to spinal cord (Fig. 14.22). They may have

Figure 14.22 Neurofibroma in left paravertebral region. This coronal T1-weighted, spin-echo image demonstrates the tumour well and shows that it does not enter the spinal canal or encroach significantly on the adjacent foramina.

characteristic high signal intensity peripherally and low signal intensity centrally (target sign) on T2-weighted images51, and enhance uniformly after gadolinium. Ten per cent of paravertebral neurofibroma and neurilemmoma extend into the spinal canal and appear as dumb-bell-shaped masses with widening of the affected neural foramen52. Malignant tumours of nerve sheath origin are rare neoplasms, typically occurring in the third to fifth decades, although they may occur earlier in patients with neurofibromatosis Type 1. Radiologically the masses are usually larger than 5 cm in diameter44. Although MRI cannot reliably differentiate benign from malignant neurogenic tumours, sudden change in size of a pre-existing mass, the development of heterogeneous signal intensity (caused by haemorrhage and necrosis), or infiltration of adjacent mediastinum or chest wall are cause for concern48.

Sympathetic ganglion tumours

Figure 14.21 Neurofibrosarcoma showing widening and pressure deformity of adjacent ribs. It was not possible to predict the malignant nature of this tumour from the plain radiographs. A benign neurofibroma would have had identical features.

Sympathetic ganglion tumours are rare neoplasms forming a continuum ranging from benign ganglioneuroma to malignant neuroblastoma, with ganglioneuroblastoma being an intermediate form44. Ganglioneuromas are benign neoplasms usually occurring in children and young adults. Ganglioneuroblastomas exhibit variable degrees of malignancy and usually occur in children53. Neuroblastomas are highly malignant tumours that typically occur in children younger than 5 years of age53. The posterior mediastinum is the most common extra-abdominal location of a neuroblastoma. Ganglioneuromas and ganglioneuroblastomas usually arise from the sympathetic ganglia in the posterior mediastinum and therefore usually present radiologically as well-defined elliptical masses, with a vertical orientation, extending over the anterolateral aspect of three to five vertebral bodies44,54. Calcification occurs in approximately 25%. CT appearance is variable44. On MRI ganglioneuromas and ganglioneuroblastomas

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are usually of homogeneous intermediate signal intensity on T1- and T2-weighted images. Neuroblastomas are typically more heterogeneous due to areas of haemorrhage, necrosis, cystic degeneration and calcium. They may be locally invasive and have a tendency to cross the midline48.

Mediastinal paragangliomas Intrathoracic paragangliomas are of two types: chemodectomas or phaeochromocytomas (functioning paragangliomas), either of which may be benign or malignant. Almost all intrathoracic chemodectomas are in a location close to the aortic arch and are classified as aortic body tumours. Other mediastinal chemodectomas are very rare55.They are usually single, but multicentric cases are reported. Fewer than 2% of phaeochromocytomas occur in the chest. Most intrathoracic phaeochromocytomas are found in the posterior mediastinum or closely related to the heart, particularly in the wall of the left atrium or the interatrial septum. Approximately one-third of mediastinal phaeochromocytomas are nonfunctioning and asymptomatic, the remainder presenting with the symptoms, signs and laboratory findings of overproduction of catecholamines. The various paragangliomas have similar appearances on chest radiography, CT and MRI. They form rounded, soft tissue masses, which are usually very vascular and therefore enhance intensely on CT56. On MRI, phaeochromocytomas usually show a signal intensity similar to muscle on T1-weighted images and very high signal intensity on T2weighted images57. MRI is particularly useful for demonstrating intracardiac phaeochromocytomas. Radio-iodine MIBG (meta-iodobenzylguanidine) and somatostatin receptor scintigraphy both show increased activity in paragangliomas, and are useful techniques for identifying extra-adrenal phaeochromocytomas57,58.

Lateral thoracic meningocele Lateral thoracic meningoceles are protrusions of the spinal meninges through an intervertebral foramen. Like neurofibromas, they are commonly associated with neurofibromatosis59. They are rare lesions that present as an asymptomatic mass, often with pressure deformity of the adjacent bone, indistinguishable on plain radiographs from neurofibromas. CT and MRI can both indicate the correct diagnosis by showing the mass to be fluid filled rather than solid44. If necessary, the diagnosis can be established by CT with intrathecal contrast medium demonstrating flow into the lesion.

Extramedullary haematopoiesis Extramedullary haematopoiesis is a rare phenomenon caused by compensatory expansion of bone marrow in various anaemias, particularly congenital haemolytic anaemias. The mass itself almost never causes symptoms. Radiographically, extramedullary haematopoietic tissue typically produces one or more smooth, lobular or spherical masses in the paravertebral gutter, usually in the lower thorax (Fig. 14.23).The bones may be normal or may show an altered lacelike trabecular pattern due to marrow expansion. The masses are usually of homogeneous soft tissue attenuation on CT, although occasionally,

Figure 14.23 Extramedullary haematopoiesis showing smooth pleurally-based masses and altered bone texture in this patient with thalassaemia. There is also a small right pleural effusion.

a fatty component may be visible60. Usually the masses are bilateral and reasonably symmetrical.

Mesenchymal tumours and tumour-like conditions Lymphangiomas (cystic hygromas) Lymphangiomas (cystic hygromas) are focal mass-like congenital malformations of the lymphatic system comprising complex lymph channels or cystic spaces containing clear or strawcoloured fluid. Lymphangiomas can occur in any part of the mediastinum, but are most common in the anterior or superior mediastinum. Mediastinal lymphangiomas may on occasion be wholly confined to the mediastinum but they are more frequently an extension from a lymphangioma in the neck. Most cervicomediastinal lymphangiomas present in early life as a neck mass, whereas the purely mediastinal lymphangiomas usually present in older children and adults as an asymptomatic mediastinal mass. Typically they appear as cystic masses, with the attenuation of the contents close to that of water on CT61.

Fatty tumours of the mediastinum Fatty tumours of the mediastinum are rare. On chest radiography, regardless of whether they are benign or malignant, fatty tumours are seen as well-defined round or oval mediastinal masses. Benign lipomas are soft and do not, therefore, compress surrounding structures unless they are very large. On CT they show uniform fat attenuation apart from a few strands of soft tissue62. Mediastinal liposarcomas are malignant fat-containing tumours.They often occur in the anterior mediastinum where the fat appears heterogeneous on CT. In contradistinction to benign lipomas, they usually contain large areas of soft tissue density material. Lipoblastoma, a benign tumour of childhood, contains fat and soft tissue63,64. Occasionally, the amount of fat attenuation is relatively small. Angiolipoma and myelolipoma are both benign tumours which may show a combination of soft tissue and fat attenuation on CT and therefore can be indistinguishable from liposarcoma65,66. Other mesenchymal tumours, such as benign and malignant fibrous tumours and haemangiomas, may occur anywhere in the mediastinum.

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Herniation of abdominal fat Herniation of omental and perigastric fat is a common cause of a localized fatty mass in the mediastinum.The fat may herniate through the oesophageal hiatus, the foramen of Morgagni, or the foramen of Bochdalek. Such herniations are usually readily diagnosed because of their characteristic locations. On CT or MRI, appearances consistent with fat eliminate confusion with other mediastinal masses64.

Mediastinal lipomatosis Relatively large collections of fat are often present in the cardiophrenic angles, particularly in obese subjects. These cardiophrenic fat pads may resemble a mass. Massive collections of fat throughout the mediastinum may be seen in so-called ‘mediastinal lipomatosis’, a phenomenon seen particularly in Cushing’s disease, in patients on steroid therapy and in obese subjects. When the fat deposits are extensive and symmetrical, the diagnosis is usually obvious. Localized masses may also be seen and CT is helpful in these cases since it can clearly demonstrate fat attenuation throughout the mass.

Sternal and spinal disease Disorders of the stern um and spine may give rise to anterior and posterior mediastinal masses, respectively. The conditions that are particularly likely to do so are paravertebral abscess, myeloma, metastasis, traumatic haematoma, lymphoma, and primary tumours (Figs 14.24–14.26).

Aortic aneurysms and aortic arch anomalies

Figure 14.25 Sternal destruction due to a radiation-induced sarcoma following treatment for breast carcinoma many years previously. Note the thickening of the overlying skin (arrows), the radical mastectomy and pleural effusion.

Prevascular masses Almost all masses anterior to the ascending aorta and the head and neck vessels are: 1 thyroid masses 2 thymic masses 3 germ-cell tumours/cystic teratomas 4 lymphadenopathy.

The differential diagnosis of a mediastinal mass depends on the age of the patient, the location, shape, size and characteristics of the lesion, and on the number of masses present. Location in particular is important in the differential diagnosis. This is best assessed with cross-sectional imaging, in particular CT.

Thyroid masses can usually be specifically diagnosed or excluded because of their contiguity with the thyroid gland in the neck and their high CT attenuation. In addition, many show cystic areas of attenuation close to water, as well as one or more areas of discrete calcification. Almost all masses located superiorly in the anterior mediastinum which cause focal deviation of the trachea are likely to be thyroid in origin. Thymic masses and germ-cell tumours/cystic teratomas can be thought of together, as most arise within the thymus. Clinical and laboratory features may help distinguish between

Figure 14.24 Sternal metastatic deposit. CT demonstration of bone destruction by a soft tissue mass in a patient with an adenocarcinoma of unknown primary.

Figure 14.26 Sternal destruction due to direct extension from mediastinal lymphoma. Note the soft tissue swelling and obliteration of fat planes in the right-sided pectoral muscles owing to soft tissue involvement.

These important causes of mediastinal masses are discussed in Chapter 27.

Differential diagnosis of mediastinal masses

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the two, e.g. myasthenia gravis is associated with thymoma, whereas elevated human chorionic gonadotrophin levels are seen with malignant germ-cell tumours. Fat, fluid, or teeth within an anterior mediastinal mass are pathognomonic of cystic teratoma. Rarer causes of prevascular masses are parathyroid adenoma, lymphangioma (cystic hygroma), pericardial cyst, aortic body chemodectoma, lipoma/liposarcoma or other mesenchymal tumours, or aneurysms. Many of these masses have features that permit a specific diagnosis to be made: parathyroid adenomas are usually associated with hyperparathyroidism; lymphangiomas almost always have broad contact with the root of the neck and show numerous areas of nonenhancing, water or near-water attenuation on CT; lipomas show uniform fat attenuation, apart from a few soft tissue strands; liposarcomas show an unusual mixture of fat interspersed by irregular strands or masses of soft tissue attenuation; aneurysms should be recognized by luminal enhancement; pericardial cysts are, in general, of uniform water attenuation with a thin wall of uniform thickness, and need only be considered when the mass in question is in contact with the pericardium. Mesenchymal tumours such as fibrosarcomas or haemangiomas have no distinguishing features.

Paracardiac masses The likely diagnoses for paracardiac masses in direct contact with the diaphragm are pericardial cyst, diaphragmatic hernia, fat pad or lymphadenopathy. If the mass is separated from the diaphragm, the likely differential diagnosis widens to include germ-cell, mesenchymal and pericardial tumours, cystic teratomas and thymic masses. Approximately 20% of thymomas are found in a paracardiac location, though contact with the diaphragm is very unusual. Lack of connection with the diaphragm eliminates the possibility of a diaphragmatic hernia.

Masses in the paratracheal, subcarinal and paraoesophageal regions These three regions are contained within a common fascial sheath which continues into the neck. The likely possibilities for a mass in these locations are lymphadenopathy, intrathoracic thyroid mass, developmental foregut cyst, oesophageal tumour, hiatus hernia, paraspinal mass encroaching on the middle mediastinum and aortic aneurysm. Aneurysms are readily diagnosed on CT by observing contrast enhancement of the lumen.The nature of other masses can often be predicted with reasonable certainty: nonvascular masses in the aortopulmonary window or deep to the azygos vein are almost invariably enlarged lymph nodes; bronchogenic cysts can be diagnosed with confidence if the criteria of a thin wall and contents exhibiting uniform water attenuation are met; and splitting of the trachea from the oesophagus is a characteristic shared only by thyroid masses, bronchogenic cysts, oesophageal tumours and an aberrant origin of the left pulmonary artery. Patients with oesophageal carcinoma (the most common oesophageal tumour) nearly always present with dysphagia when the tumour mass is still relatively small, whereas a leiomyoma or other mesenchymal tumour of the oesophagus may occasionally present first as an asymptomatic mediastinal mass. The intimate

• THE MEDIASTINUM, INCLUDING THE PERICARDIUM

relationship with the oesophagus usually leads to a barium swallow examination. Hiatus hernia is an exceedingly common cause of enlargement of the mediastinum in the region of the lower oesophagus and plain radiography is so characteristic that a barium swallow is rarely required for diagnosis.

Paravertebral masses Neurogenic lesions and neoplastic lymphadenopathy dominate the differential diagnosis for paravertebral masses. The less common causes of paravertebral masses include: extramedullary haematopoiesis; pancreatic pseudocyst; mesenchymal tumours such as lipoma, fibroma and haemangioma; and lesions arising from the oesophagus, pharynx, spine, or aorta. The oesophageal or pharyngeal lesions that may project posteriorly include leiomyoma, foregut duplication cyst, and congenital or acquired diverticula of the oesophagus. The spinal origin of masses such as paraspinal abscess, primary or metastatic tumours of the vertebral body, or haematoma from trauma to the spine, are usually readily diagnosed by observing corresponding changes in the spine.Aneurysms of the descending aorta that truly mimic a mediastinal mass are uncommon, as the majority of large aneurysms in this location are obvious dilatations of the descending aorta and have curvilinear calcification in their wall. An aneurysm is readily diagnosed on CT when opacification of its lumen can be demonstrated.

OTHER MEDIASTINAL LESIONS Acute mediastinitis Acute infection of the mediastinum is rare. Oesophageal perforation, either iatrogenic or from swallowed objects, is the most frequent cause. Forceful vomiting may tear the oesophageal wall (Boerhaave’s syndrome) and if the tear is deep enough, air, alimentary juices and food may leak into the mediastinum causing acute mediastinitis. Such tears are almost invariably just above the gastro-oesophageal junction. Other causes of acute mediastinal infection are leakage from the oesophagus into the mediastinum through a necrotic neoplasm, and extension of infection from the neck, retroperitoneum, or adjacent intrathoracic or chest wall structures into the mediastinum. Clinically, the patients are often very ill with an abrupt onset of high fever, tachycardia and chest pain. The chest radiograph may show widening and lack of clarity of the mediastinal outline adjacent to the oesophagus. Streaks or round collections of air may be seen within the mediastinum, and there may even be one or more mediastinal air–fluid levels. Pleural effusions are frequent and are usually confined to, or greatest on, the left. Lower lobe pneumonia or atelectasis often complicate the radiographic picture. A swallow using nonionic contrast medium may show the site of perforation, with extravasation into the mediastinum. CT shows obliteration of the normal mediastinal fat planes and gas bubbles may be identified within the mediastinum (Fig. 14.27). In advanced cases there may be walledoff discrete fluid or air–fluid collections indicating abscess formation. There may be an associated empyema, subphrenic or pericardial collection. When acute mediastinitis

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Figure 14.27 Abscess formation. (A) Abscess in anterior mediastinum demonstrated on CT. (B) This coronal reformat of an axial CT dataset demonstrates a tuberculous mediastinal abscess and associated lung changes in a different patient.

is suspected following sternotomy, CT shows the extent of inflammation and any drainable mediastinal or pericardial fluid collections67. Distinguishing a retrosternal haematoma from reactive granulation tissue or cellulitis is difficult, as is distinguishing osteomyelitis from the direct effects of the surgical incision68. It should be remembered that substernal fluid collections and dots of air are normal in the first 20 d following sternotomy. Therefore, before gas-forming infections can be diagnosed, the air collections must appear de novo or must progressively increase in the absence of any other explanation69.

Fibrosing mediastinitis Fibrosing mediastinitis (sclerosing mediastinitis or mediastinal fibrosis) is a disorder that results in proliferation of fibrous tissue and collagen within the mediastinum. It is usually due to

previous infection from histoplasmosis or tuberculosis70. The fibrosis is usually maximal in the upper mediastinum but may extend to the lung roots. The most common clinical consequences are obstruction to the superior vena cava and, occasionally, obstruction to the central pulmonary arteries or veins. Other causes of fibrosing mediastinitis include idiopathic (similar to retoperitoneal fibrosis/peri-aortitis), autoimmune disease, radiation therapy and drugs (in particular methysergide). The chest radiograph is non-specific and often underestimates the extent of mediastinal disease. In fibrosing mediastinitis due to previous tuberculous or fungal infection, the chest radiograph may show calcification of mediastinal or hilar lymph nodes. CT typically shows an infiltrative, often extensively calcified, hilar or mediastinal process (Fig. 14.28), which may be relatively focal when disease is due to previous histoplasmosis or tuberculosis, and more diffuse in the idiopathic form71. Airway

Figure 14.28 Mediastinitis. (A) Fibrosing mediastinitis. There is confluent soft tissue infiltration throughout the mediastinum without evidence of a discrete mass. Note the marked narrowing of the superior vena cava (SVC). The patient had clinical evidence of SVC compression and a history of previous radiotherapy for lymphoma, diagnosed by surgical biopsy through a median sternotomy. This original biopsy, 30 years previously, had been complicated by post-operative infection. (B) Tracheal narrowing from mediastinal fibrosis of unknown cause in a different patient. The trachea (arrow) is markedly narrowed and distorted and lies within the fibrotic scarring. The more posterior oesophagus is relatively dilated and gas filled.

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narrowing (Fig. 14.28), vascular encasement and obstruction may also be seen. MRI provides similar information to CT, with the fibrosis appearing as heterogeneous signal intensity on T1and T2-weighted imaging72, but lacks sensitivity for detection of calcification, which is an important feature for differentiating fibrosing mediastinitis from other infiltrative disorders of the mediastinum, such as lymphoma and metastatic carcinoma.

Mediastinal haemorrhage Mediastinal haemorrhage is most commonly due to trauma to the arteries and veins within the mediastinum, with other causes including rupture of an aneurysm, aortic dissection and complications of central venous catheterization. Radiologically haemorrhage produces an increase in the mediastinal diameter which is maximal at the point of bleeding73. Blood may track through the mediastinum, frequently running over the apex of the left lung to produce a smooth and well-defined apical cap. When haemorrhage is severe blood may rupture into the pleural cavity or dissect into lung along peribronchovascular sheaths, resulting in a radiographic pattern resembling interstitial oedema. On unenhanced CT, acute haemorrhage may appear of relative high attenuation. The appearance of mediastinal haematoma on MRI varies with the age of the haemorrhage.

Mediastinal emphysema Air may enter the mediastinum from a perforation of the pharynx, oesophagus, or major airways. In many instances, however, a pneumomediastinum is the result of an air leak from a tear in a small intrapulmonary airway, the air dissecting through the lung via the hilum into the mediastinum. Asthma is the most common precipitating cause. In other cases the leak is probably related to abrupt changes in intrathoracic pressure such as those associated with vomiting. Occasionally, air tracks into the mediastinum from retroperitoneal air collections. The presence of a pneumomediastinum is, in itself, of little significance (though it may be responsible for substernal chest pain), but the condition causing the air leak (particularly bronchial, oesophageal, or pharyngeal perforation) may be of great significance to the patient. On imaging the condition is recognized as streaky translucencies within the mediastinum that are usually most obvious adjacent to the left heart border, aortic knuckle, main pulmonary artery and adjacent left hilum (Fig. 14.29). The air dissects through

Figure 14.29 Mediastinal emphysema in a patient with Pneumocystis jiroveci (formerly carinii) pneumonia. The air has tracked through the mediastinum into the neck and chest wall.

the perivascular areolar tissues and may track up into the neck, supraclavicular areas and axillae, as well as down into the retroperitoneum. It may also track extraserosally on either side of the diaphragm, which will occasionally be seen as a continuous line of transradiancy known as the ‘continuous diaphragm sign’74. The differential diagnosis of a pneumomediastinum on chest radiograph includes a medially placed pneumothorax and a ‘Mach effect’ due to the abrupt change in density between the lung and the adjacent heart and mediastinum. It is easy to appreciate why a medial pneumothorax can be mistaken for a pneumomediastinum, since in both instances there is a linear collection of air bounded on its lateral side by a thin line of pleura. Deciding whether the line is mediastinal parietal pleura or visceral pleura can be difficult; the distinction often depends on recognizing the full extent of the air and looking carefully for a pneumothorax lying against the chest wall, or looking for evidence of air elsewhere in the mediastinum. Pneumomediastinum is easy to diagnose on CT as streaks or rounded collections of air surrounding the vessels and other structures within the mediastinum.

THE PERICARDIUM NORMAL ANATOMY The pericardium is a fibrous bag consisting of the (inner) visceral pericardium, the (outer) parietal pericardium, and the 20–60-ml cavity between them (Fig. 14.30). Beneath the visceral pericardium is either myocardium or epicardial fat. The visceral pericardium extends for short distances along the pulmonary veins, the superior vena cava below the azygos vein, the inferior vena cava, and the ascending aorta to

a point 20–30 mm above the aortic root and the main pulmonary artery as far as its bifurcation. It then reflects upon itself to become the parietal pericardium. The reflection of the two pericardial layers around the great arteries and veins forms the two ‘appendages’ or diverticula of the pericardium. The arterial mesocardium is an anterior extension of all layers of the pericardium around the ascending aorta and pulmonary trunk. It lies obliquely in the coronal plane and is higher on the right, over the ascending aorta, than on the

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Superior vena cava

Transverse pericardial sinus

Ascending aorta Pulmonary trunk

Left pulmonary veins Right pulmonary veins Oblique pericardial sinus Inferior vena cava

Diaphragm

Pericardium (cut edge)

Diaphragmatic part of pericardium

A Figure 14.30 The normal pericardium. (A) Drawing of the reflections of the normal pericardial sac. (B) The normal pericardium on narrow-section CT is demonstrated as a thin (1–2 mm) soft tissue density line separated from the cardiac muscle by the epicardial fat (arrows).

left, over the pulmonary trunk. The arterial mesocardium is divided into an anterior compartment (the pre-aortic recess), lying between the ascending aorta and pulmonary trunk, and another compartment behind the ascending aorta immediately above the right pulmonary artery (the retroaortic recess) (Fig. 14.31). Posterior and lateral to the heart, the extraparenchymal pulmonary veins and the superior and inferior venae cavae are enveloped by the venous mesocardium, which has the shape of an inverted U. Beneath the apex of the U is the space between the pulmonary veins and the left atrium—the oblique sinus. The arterial and venous

mesocardia are connected by the transverse sinus. This space is limited anteriorly by the aorta and pulmonary arteries, and posteriorly by the superior vena cava and left atrium. It forms a communication, at the base of the heart, between the right and left sides of the pericardial cavity. The pericardium is considered to support the heart and cardiac function in three major ways: it contains the heart and limits its motion within the middle mediastinum; it acts as a protective membrane to shield the heart from local inflammatory disease; and it limits excessive acute dilatation of the cardiac chambers in response to increased preload75.

Figure 14.31 Contrast-enhanced CT demonstrating normal pericardial recesses. (A) The retro-aortic recess appears as a crescentic structure closely apposed to the posterior wall of the aorta (arrows). It is characteristically of slightly lower attenuation than the unenhanced blood pool. In this example of a patient in mild cardiac failure there is slightly more fluid than is usually seen. (B) Pericardial fluid in the anterior compartment (pre-aortic recess) (arrows).

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On the lateral chest radiograph the normal pericardium may be seen as a 1–2-mm thick curved stripe anterior to the heart, set between more radiolucent mediastinal fat anteriorly and epicardial fat posteriorly. The visceral pericardium is normally very thin and is therefore not visualized separately by any imaging modality. The combination of the visceral pericardium and the small layer of physiological pericardial fluid constitutes the normal pericardium routinely visualized on CT and MRI as a 1–2-mm thick layer76,77 (Fig. 14.30B), which can appear focally thicker at the sites of its major attachments. Although the pericardium is readily visualized overlying the right atrium and right ventricle in most individuals, it is often not visible over the lateral and inferior walls of the left ventricle. It is essential to appreciate the anatomical extent and location of the pericardial recesses78 since they are frequently seen on both CT79,80 and MRI and may be confused with aortic dissection, adenopathy, a mediastinal mass, or thymus.

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collections and masses. Limitations of MRI include its inability to reliably depict calcification, relatively longer data acquisition times, and greater demands on the patient with regard to cooperation with breath-holding. Additionally, arrhythmias, which commonly occur in association with pericardial disease, may detrimentally affect image acquisition and quality.

DEVELOPMENTAL ANOMALIES Congenital absence of the pericardium

Computed tomography is the best investigation for localizing, characterizing and demonstrating the extent of a collection or mass in the acute setting. Multidetector CT (MDCT) with multiplanar reformats, particularly if ECG gated, provides excellent motion-free assessment of the pericardium. MDCT has the advantage of speed and generally greater availability and accessibility. It is highly sensitive for the detection of pericardial calcification, an important finding in constrictive pericarditis. Pericardial assessment with CT may be limited by motion artefact if not ECG gated; additionally, differentiating pericardial fluid from thickening may occasionally be difficult on CT.

Compromise of the vascular supply to the pleuropericardial membrane during embryological development is associated with congenital defects in the pericardium. Pericardial deficiency is associated with congenital anomalies of the heart and lungs, including atrial septal defect, tetralogy of Fallot, patent ductus arteriosus, bronchogenic cysts and pulmonary sequestration81. The defects vary in size from small communications between the pleural and pericardial cavities to complete (bilateral) absence of the pericardium. The most common form is complete absence of the left pericardium, with preservation of the pericardium on the right. Bilateral and isolated right-sided lesions are very rare. Pericardial defects are frequently associated with large defects in the parietal pleura, through which the left lung can herniate and surround the intrapericardial vascular structures82,83. Complete absence of the pericardium is usually asymptomatic, whereas partial or localized absence of the pericardium may be complicated by herniation and entrapment of a cardiac chamber, in particular the left atrial appendage in left-sided defects. Chest radiograph findings are frequently subtle and nonspecific82,83. When present, chest radiograph findings in complete absence of the left pericardium include displacement of the heart into the left chest and interposition of lung between the aorta and pulmonary artery, as well as between the left hemidiaphragm and cardiac silhouette. Both the medial and lateral borders of the main pulmonary artery may be visualized more clearly due to absence of the anterior pericardial reflection between the aorta and the pulmonary artery. Due to leftward displacement and rotation, the right cardiac border may not be seen. In partial pericardial defects, varying degrees of prominence of the pulmonary artery and/or left atrial appendage may be seen, while the heart retains its normal position in the thorax82 (Figs 14.32, 14.33). A definitive diagnosis of absence of the pericardium can be obtained with either CT or MRI.

Magnetic resonance imaging

Pericardial cysts and diverticula

Magnetic resonance imaging can provide a comprehensive assessment of the pericardium. When T1- and T2-weighted imaging sequences (a number of which can be performed using ECG-gated breath-hold techniques), are combined with gradient-echo cine-based functional cardiac imaging, both pericardial disease and its impact on cardiac function can be assessed. MRI has some advantages over echocardiography and CT in the detection and characterization of pericardial

Pericardial cysts and diverticula are thought to be the result of persistence of blind-ending ventral parietal pericardial recesses. Those cysts that communicate with the pericardial space are termed pericardial diverticula. They almost invariably appear as a well-defined, oval or occasionally lobulated mass attached to the pericardium84 (Fig.14.34). Most occur in the right cardiophrenic angle, with a proportion being situated in the left cardiophrenic angle and some higher in the

IMAGING PERICARDIAL DISEASE Chest radiography Chest radiography is of limited use in the detailed assessment of pericardial disease although pericardial effusions, calcification and secondary signs and complications of pericardial disease may be evident.

Ultrasound Ultrasound is the most commonly used investigation in the initial evaluation of pericardial disease. Restricted acoustic windows limit its evaluation of the entire pericardium. Loculated collections, intrapericardial blood clot and pericardial thickening in particular may be difficult to assess or may be overlooked.

Computed tomography

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Figure 14.32 Complete absence of the pericardium. (A) PA radiograph. The heart is displaced into the left chest, obscuring the right heart border by the spine. The cardiac apex (arrow) is elevated, and air-filled lung is seen beneath it. (B) On lateral barium swallow, the increased density of the left ventricle surrounded by the air-filled lung (arrows) is apparent.

Figure 14.33 Partial absence of the pericardium. Axial spin-echo MRI. (A) Image through the aortic valve and proximal ascending aorta (Ao). The heart is displaced into the left chest and rotated in a clockwise manner. (B) Image 1-cm cephalad through the pulmonary valve (PV). A sliver of lung (arrow) invaginates to come into contact with the ascending aorta. (C) Image 1-cm cephalad to the main (MP) and transverse right (RP) pulmonary arteries. The MP protrudes to the left and is in contact with the lung.

Figure 14.34 Pericardial cyst. Axial spin-echo MRI at the base of the heart. (A) An intermediate signal intensity smooth mass extrinsic to the heart is identified (arrow). Ao = ascending aorta, LA = left atrium, PA = main pulmonary artery, S = superior vena cava. (B) Chest radiograph, lateral view. The smooth lobulated density superimposed on the cardiac silhouette (arrows) is a pericardial cyst.

PA Ao S LA

A

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mediastinum. They contain clear fluid and can be recognized as fluid-filled cysts surrounded by normal pericardium on echocardiography, CT, or MRI85, the cyst contents showing characteristics similar to water.

Intrapericardial bronchogenic cysts Intrapericardial bronchogenic cysts are rare. They may cause symptoms secondary to mass effect on adjacent cardiac structures. Appearances are similar to bronchogenic cysts occurring elsewhere in the mediastinum.

ACQUIRED PERICARDIAL DISEASE Pericarditis including pericardial effusion Inflammation of the pericardium (pericarditis) may occur in response to a variety of insults. It typically results in cellular proliferation, or the production of fluid (pericardial effusion) or fibrin, either alone or in combination. Causes include myocardial infarction (acute or post-myocardial infarction [Dressler] syndrome), pericardiotomy, mediastinal irradiation, infection (viral or bacterial), connective tissue disease (rheumatoid arthritis, systemic lupus erythematosus), metabolic disorders (uraemia, hypothyroidism), neoplasia and AIDS. The most common imaging manifestation of acute pericarditis is a pericardial effusion, the nature of the fluid varying with the underlying cause (Fig. 14.35). Transudative pericardial effusions may develop after cardiac surgery or in congestive heart failure, uraemia, post-pericardiectomy syndrome, myxoedema and collagen–vascular diseases. Haemopericardium may be due to trauma, aortic dissection, aortic rupture, or neoplasm (especially primary pericardial mesothelioma) (Fig. 14.35). Chylopericardium resulting from injury or obstruction of the thoracic duct is rare. On chest radiograph sudden increase in the size of the cardiac silhouette without specific chamber enlargement suggests the diagnosis of pericardial effusion. Filling in of the retrosternal space, effacement of the normal cardiac borders, development of a ‘flask’ or ‘water bottle’ cardiac conFiguration, and bilateral hilar overlay are features of pericardial

• THE MEDIASTINUM, INCLUDING THE PERICARDIUM

effusion (Fig. 14.36). The epicardial fat pad ‘sign’ is positive when, visualized in the lateral projection, an anterior pericardial stripe (bordered by epicardial fat posteriorly and mediastinal fat anteriorly) is thicker than 2 mm. This sign is diagnostic of pericardial thickening or fluid86,87. Echocardiography is the most commonly used method for diagnosing pericardial effusion. It is highly sensitive and specific although visualization may be limited in patients with marked obesity or emphysema, and loculated collections and intrapericardial clot in postoperative patients may be difficult to detect88. CT and MRI are indicated when a loculated or haemorrhagic effusion or pericardial thickening is suspected. Increased attenuation in a pericardial effusion on CT suggests haemorrhage89 (see Fig. 14.35), although occasionally the attenuation values of a haemorrhagic effusion may overlap with the pericardial fluid found in patients with hypothyroidism. On spin-echo MRI, the signal characteristics of pericardial collections vary depending on the composition of the fluid. In the absence of haemorrhage, effusions are typically of predominantly low signal intensity, although intermediate signal intensity may be seen in inflammatory conditions such as uraemia, tuberculosis, or trauma, possibly reflecting high protein content and when more focal, the presence of adhesions limiting normal flow of pericardial fluid in the pericardial space77,85. In haemorrhagic effusions, signal intensity varies depending on the age of blood products. Thickened inflamed pericardium can appear of moderate to high signal intensity on spin-echo MRI, and pericardial enhancement may be seen on both MRI or CT performed after intravenous contrast medium administration.

Constrictive pericarditis Any insult to the pericardium can progress from an acute pericarditis with pericardial effusion to a subacute stage of resorption of the effusion with organization, and then to a chronic phase of fibrous scarring, pericardial thickening and obliteration of the pericardial cavity. Constrictive pericarditis is the condition in which a thickened, fibrotic and often calcified pericardium restricts diastolic filling of the heart (Fig. 14.37).

Figure 14.35 Pericardial effusion. (A) Small pericardial effusion is present in the anterior pericardial sac in a patient with advanced pulmonary artery hypertension. Note the dilated right-sided cardiac chambers. (B) Large haemopericardium complicating a type A aortic dissection. This is an unenhanced image and the haemopericardium is the same density as soft tissue structures (compare to A). (C) The dissection flap can be seen on this enhanced CT within the transverse arch.

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Figure 14.36 Large pericardial effusion. (A) The heart had become rapidly enlarged in this patient who had previously undergone aortic valve replacement. (B) Lateral view demonstrates the pleural fluid lying posteriorly. (C) Unenhanced CT through the level of the valve replacement demonstrates the large pericardial effusion.

Figure 14.37 Dense pericardial calcification demonstrated on (A,B) chest radiograph (arrows) and (C) CT. There are bilateral pleural effusions in this patient with constrictive calcific pericarditis due to previous tuberculosis.

Constrictive pericarditis is usually the result of a chronic pericardial insult. The aetiology is unknown in many cases, presumed to be secondary to an occult viral pericarditis and other causes of pericarditis90. Outside the USA, the most common cause is probably tuberculosis or fungal aetiology. Constriction due to neoplastic infiltration of the pericardium is most commonly secondary to carcinoma of the lung or breast, lymphoproliferative malignancies and melanoma. Pericardial constriction after mediastinal irradiation, usually performed to treat breast carcinoma or Hodgkin’s disease, may occur months to years after treatment91. Pericardial thickening is seen in up to 88% of confirmed cases of constrictive pericarditis92. In the majority of cases, constrictive pericarditis involves the entire pericardium, restricting filling of all cardiac chambers. Occasionally, in particular anterior to the right ventricle in postoperative patients, the pericardial thickening is more localized78. Patients with constrictive pericarditis frequently present with symptoms of heart failure such as dyspnoea, orthopnoea and fatigability; they may occasionally present with hepatomegaly and ascites. The clinical findings of constriction overlap with those of restrictive cardiomyopathy, a primary disorder of the myocardium. The differential diagnosis is important since the patients with pericardial constriction may benefit from

pericardiectomy, while restrictive cardiomyopathy is managed medically or by cardiac transplantation. The hallmarks of pericardial constriction are pericardial thickening, pericardial calcification and abnormal diastolic ventricular function. On chest radiograph the heart size may be normal or appear increased due to the presence of pericardial fluid. The superior vena cava and azygos vein may be of increased size due to raised right heart pressures. Although echocardiography is routinely performed and provides an excellent assessment of haemodynamic function, it is not highly accurate at depicting pericardial thickening. CT and MRI are significantly more sensitive, with CT having the added advantage over MRI of being able to demonstrate the presence of calcification, which is associated with pericardial constriction (see Fig. 14.37C). Pericardial thickening of 4 mm or more is abnormal and, when accompanied by clinical features of constriction, is highly suggestive of constrictive pericarditis85,92. Both CT and MRI may show the secondary effects of constriction on the central cardiovascular structures. The right ventricle tends to be of reduced volume and has a narrow tubular configuration. A sigmoid-shaped interventricular septum or prominent leftward convexity of the septum may be seen78. The right atrium,

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• THE MEDIASTINUM, INCLUDING THE PERICARDIUM

superior and in particular inferior venae cavae, and hepatic veins may be dilated. Hepatomegaly and ascites may be seen. Cardiac MRI can also be used to provide a more detailed assessment of cardiac function and myocardial wall thickness, which has prognostic implications for outcome after pericardiectomy.

Cardiac tamponade Gradual accumulation of pericardial fluid may fail to produce clinical signs or symptoms for an extended period of time. However, rapid accumulation of as little as 100–200 ml of fluid can cause a haemodynamically significant compression of the heart, which severely impedes diastolic filling, the condition known as pericardial tamponade. Even in the face of preserved ejection fraction, diminished ventricular end-diastolic volume leads to reduced stroke volume. In addition to other clinical signs of pericardial effusion, those of cardiac tamponade include pulsus paradoxus, which is exaggeration of the normal inspiratory drop in systolic blood pressure. Since acute tamponade may occur with small effusions, clinically important pericardial enlargement may be difficult to detect on plain radiographs. Subtle changes in cardiac contour may only be detectable by comparison with previous studies. If there is decreased pulmonary vascularity in spite of the cardiac enlargement or if the superior vena cava and azygos veins are dilated, tamponade should be suspected. Echocardiographic demonstration of pericardial effusion and the clinical findings are usually sufficient to make the diagnosis of tamponade. CT and MRI are frequently instrumental in suggesting the cause of the effusion (i.e. haemorrhage, neoplastic involvement, inflammation due to tuberculosis, or other infectious processes, etc).

Pericardial neoplasms Primary pericardial neoplasms are rare, with approximately equal incidence of benign versus malignant pericardial neoplasms. Benign tumours include teratomas, fibromas, neurofibromas, lipomas, haemangiomas, lymphangiomas and hamartomas. Although these patients are usually symptom free, pericardial effusion or constriction, particularly in the case of childhood teratomas, may occur.

Figure 14.38 Phaeochromocytoma of the heart. There is abnormal soft tissue in the right atrioventricular groove (arrows) that proved to be a primary cardiac phaeochromocytoma on histological examination following resection.

in approximately 10% of all patients with malignancy94. The most common malignancies encountered are lung, lymphoma, breast, leukaemia, stomach, melanoma, liver and colon94 (Fig. 14.39). A pericardial effusion is the most common finding in pericardial malignancy, whether primary pericardial or metastatic. Intrapericardial neoplasms tend to compress and deform normal intrapericardial structures, whereas extrapericardial masses tend to displace the intrapericardial structures without compression or distortion. Chest radiographs are often abnormal, but are non-specific. Alteration of fat-pad contours, cardiac enlargement, mediastinal widening, hilar adenopathy, or a hilar mass may be seen. Echocardiography is usually the initial technique for evaluation of a suspected pericardial neoplasm, with MRI and CT being useful for further evaluation. Both MRI and CT are excellent at providing information regarding the size, location and extent of pericardial neoplasms, but are not tissue specific. Fatty tumours (lipomas, fat-containing teratomas) are the exception, due to their typically low attenuation on CT and increased signal intensity on spin-echo T1-weighted MRI. Fatty tumours must be differentiated from the focal

Malignant mesothelioma Malignant mesothelioma is the most common primary pericardial malignancy. A causal relationship between it and asbestosis is uncertain because of the low prevalence of this neoplasm. Mesothelioma may present as a well-defined single mass, multiple nodules, or diffuse plaques involving the visceral and parietal pericardium and wrapping around the cardiac chambers and great vessels. Clinically it presents with haemorrhagic effusion and tamponade, congestive heart failure, arrhythmia and occasionally pericardial constriction93. Other malignant primary tumours include lymphoma, sarcoma, phaeochromocytoma and liposarcoma (Fig. 14.38).Teratomas of the pericardium may also be malignant and are most commonly seen in children.

Pericardial metastases Pericardial metastases are much more common than primary pericardial neoplasms. They are identified at autopsy

Figure 14.39 Metastatic melanoma. There is a mass within the right atrial cavity that demonstrates high signal intensity on this T1-weighted image in keeping with the known diagnosis of metastatic malignant melanoma (arrows). Note the enlarged left axillary lymph nodes.

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deposits of subepicardial fat and non-neoplastic lesions that can simulate fatty tumours, such as mesenteric fat in a hiatal hernia. Metastatic melanoma may have high signal intensity on T1- and T2-weighted images (see Fig. 14.40)95, a feature that may be useful in differentiating it from other metastatic neoplasms, which are frequently of low signal intensity on T1and high signal intensity on T2-weighted images96. In addition to discrete masses and effusions, metastatic involvement of the pericardium may cause focal or diffuse pericardial thickening, which may be irregular and usually enhances. Primary lipoma, liposarcoma and lymphoma of the pericardium typically appear as large heterogeneous masses frequently associated with a serosanguinous pericardial effusion93.

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44. Strollo D C, Rosado-de-Christenson M L, Jett J R 1997 Primary mediastinal tumors: part II. Tumors of the middle and posterior mediastinum. Chest 112: 1344–1357 45. Nakata H, Nakayama C, Kimoto T et al 1982 Computed tomography of mediastinal bronchogenic cysts. J Comput Assist Tomogr 6: 733–738 46. Mendelson D S, Rose J S, Efremidis S C, Kirschner P A, Cohen B A 1983 Bronchogenic cysts with high CT numbers. Am J Roentgenol 140: 463–465 47. Kawashima A, Fishman E K, Kuhlman J E, Nixon M S 1991 CT of posterior mediastinal masses. RadioGraphics 11: 1045–1067 48. Erasmus J J, McAdams H P, Donnelly L F, Spritzer C E 2000 MR imaging of mediastinal masses. Magn Reson Imaging Clin North Am 8: 59–89 49. Reed J C, Hallet K K, Feigin D S 1978 Neural tumors of the thorax: subject review from the AFIP. Radiology 126: 9–17 50. Kumar A J, Kuhajda F P, Martinez C R, Fishman E K, Jezic D V, Siegelman S S 1983 Computed tomography of extracranial nerve sheath tumors with pathological correlation. J Comput Assist Tomogr 7: 857–865 51. Bhargava R, Parham D M, Lasater O E, Chari R S, Chen G, Fletcher B D 1997 MR imaging differentiation of benign and malignant peripheral nerve sheath tumors: use of the target sign. Pediatr Radiol 27: 124–129 52. Aughenbaugh GL 1984 Thoracic manifestations of neurocutaneous diseases. Radiol Clin North Am 22: 741–756 53. Adam A, Hochholzer L 1981 Ganglioneuroblastoma of the posterior mediastinum: a clinicopathologic review of 80 cases. Cancer 47: 373–381 54. Bar-Ziv J, Nogrady M B 1975 Mediastinal neuroblastoma and ganglioneuroma. The differentiation between primary and secondary involvement on the chest roentgenogram. Am J Roentgenol Radium Ther Nucl Med 125: 380–390 55. Olson J L, Salyer W R 1978 Mediastinal paragangliomas (aortic body tumor): a report of four cases and a review of the literature. Cancer 41: 2405–2412 56. Spizarny D L, Rebner M, Gross B H 1987 CT evaluation of enhancing mediastinal masses. J Comput Assist Tomogr 11: 990–993 57. van Gils A P, Falke T H, van Erkel A R et al 1991 MR imaging and MIBG scintigraphy of pheochromocytomas and extraadrenal functioning paragangliomas. RadioGraphics 11: 37–57 58. Krenning E P, Kwekkeboom D J, Bakker W H et al 1993 Somatostatin receptor scintigraphy with [111In-DTPA-D-Phe1]- and [123I-Tyr3]octreotide: the Rotterdam experience with more than 1000 patients. Eur J Nucl Med 20: 716–731 59. Miles J, Pennybacker J, Sheldon P 1969 Intrathoracic meningocele. Its development and association with neurofibromatosis. J Neurol Neurosurg Psychiatry 32: 99–110 60. Long J A Jr, Doppman J L, Nienhuis A W 1980 Computed tomographic studies of thoracic extramedullary hematopoiesis. J Comput Assist Tomogr 4: 67–70 61. Shaffer K, Rosado-de-Christenson M L, Patz E F Jr, Young S, Farver C F 1994 Thoracic lymphangioma in adults: CT and MR imaging features. Am J Roentgenol 162: 283–289 62. Glazer H S, Wick M R, Anderson D J et al 1992 CT of fatty thoracic masses. Am J Roentgenol 159: 1181–1187 63. Whyte A M, Powell N 1990 Mediastinal lipoblastoma of infancy. Clin Radiol 42: 205–206 64. Gaerte S C, Meyer C A, Winer-Muram H T, Tarver R D, Conces D J Jr 2002 Fat-containing lesions of the chest. RadioGraphics 22: 615–678 65. Kline M E, Patel B U, Agosti S J 1990 Noninfiltrating angiolipoma of the mediastinum. Radiology 175: 737–738 66. Kim K, Koo B C, Davis J T, Franco-Saenz R 1984 Primary myelolipoma of mediastinum. J Comput Tomogr 8: 119–123 67. Jolles H, Henry D A, Roberson J P, Cole T J, Spratt J A 1996 Mediastinitis following median sternotomy: CT findings. Radiology 201: 463–466 68. Bitkover C Y, Cederlund K, Aberg B, Vaage J 1999 Computed tomography of the sternum and mediastinum after median sternotomy. Ann Thorac Surg 68: 858–863 69. Carter A R, Sostman H D, Curtis A M, Swett H A 1983 Thoracic alterations after cardiac surgery. Am J Roentgenol 140: 475–481

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70. Goodwin R A, Nickell J A, Des Prez R M 1972 Mediastinal fibrosis complicating healed primary histoplasmosis and tuberculosis. Medicine Balt 51: 227–246 71. Sherrick A D, Brown L R, Harms G F, Myers J L 1994 The radiographic findings of fibrosing mediastinitis. Chest 106: 484–489 72. Rossi S E, McAdams H P, Rosado-de-Christenson M L, Franks T J, Galvin J R 2001 Fibrosing mediastinitis. RadioGraphics 21: 737–757 73. Woodring J H, Loh F K, Kryscio R J 1984 Mediastinal hemorrhage: an evaluation of radiographic manifestations. Radiology 151: 15–21 74. Bejvan S M, Godwin J D 1996 Pneumomediastinum: old signs and new signs. Am J Roentgenol 166: 1041–1048 75. Holt JP 1970 The normal pericardium. Am J Cardiol 26: 455–465 76. Bull R K, Edwards P D, Dixon A K 1998 CT dimensions of the normal pericardium. Br J Radiol 71: 923–925 77. Sechtem U, Tscholakoff D, Higgins C B 1986 MRI of the normal pericardium. Am J Roentgenol 147: 239–244 78. Rienmuller R, Groll R, Lipton M J 2004 CT and MR imaging of pericardial disease. Radiol Clin North Am 42: 587–601, vi 79. Groell R, Schaffler G J, Rienmueller R 1999 Pericardial sinuses and recesses: findings at electrocardiographically triggered electron-beam CT. Radiology 212: 69–73 80. Budoff M J, Lu B, Mao S et al 2000 Evaluation of fluid collection in the pericardial sinuses and recesses: noncontrast-enhanced electron beam tomography. Invest Radiol 35: 359–365 81. Spodick D H 2001 Pericardial disease. In: Braunwald E (ed) Heart disease: a textbook of cardiovascular medicine. WB Saunders, Philadelphia, pp 1823–1876 82. Nasser W K, Helmen C, Tavel M E, Feigenbaum H, Fisch C 1970 Congenital absence of the left pericardium. Clinical, electrocardiographic, radiographic, hemodynamic, and angiographic findings in six cases. Circulation 41: 469–478 83. Van Son J A, Danielson G K, Schaff H V, Mullany C J, Julsrud P R, Breen J F 1993 Congenital partial and complete absence of the pericardium. Mayo Clin Proc 68: 743–747 84. Feigin D S, Fenoglio J J, McAllister H A, Madewell J E 1977 Pericardial cysts. A radiologic-pathologic correlation and review. Radiology 125: 15–20 85. Sechtem U, Tscholakoff D, Higgins C B 1986 MRI of the abnormal pericardium. Am J Roentgenol 147: 245–252 86. Lane E J Jr, Carsky E W 1968 Epicardial fat: Lateral plain film analysis in normals and in pericardial effusion. Radiology 91: 1–5 87. Carsky E W, Mauceri R A, Azimi F 1980 The epicardial fat pad sign: analysis of frontal and lateral chest radiographs in patients with pericardial effusion. Radiology 137: 303–308 88. Yousem D, Traill T T, Wheeler P S, Fishman E K 1987 Illustrative cases in pericardial effusion misdetection: correlation of echocardiography and CT. Cardiovasc Intervent Radiol 10: 162–167 89. Tomoda H, Hoshiai M, Furuya H et al 1980 Evaluation of pericardial effusion with computed tomography. Am Heart J 99: 701–706 90. Cameron J, Oesterle S N, Baldwin J C, Hancock E W 1987 The etiologic spectrum of constrictive pericarditis. Am Heart J 113: 354–360 91. Ling L H, Oh J K, Schaff H V et al 1999 Constrictive pericarditis in the modern era: evolving clinical spectrum and impact on outcome after pericardiectomy. Circulation 100: 1380–1386 92. Masui T, Finck S, Higgins C B 1992 Constrictive pericarditis and restrictive cardiomyopathy: evaluation with MR imaging. Radiology 182: 369–373 93. Grebenc M L, Rosado de Christenson M L, Burke A P, Green C E, Galvin J R 2000 Primary cardiac and pericardial neoplasms: Radiologic– pathologic correlation. RadioGraphics 20: 1073–1103 94. Abraham K P, Reddy V, Gattuso P 1990 Neoplasms metastatic to the heart: review of 3314 consecutive autopsies. Am J Cardiovasc Pathol 3: 195–198 95. Mousseaux E, Meunier P, Azancott S, Dubayle P, Gaux J C 1998 Cardiac metastatic melanoma investigated by magnetic resonance imaging. Magn Reson Imaging 16: 91–95 96. Fujita N, Caputo G R, Higgins C B 1994 Diagnosis and characterization of intracardiac masses by magnetic resonance imaging. Am J Card Imaging 8: 69–80

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SUGGESTIONS FOR FURTHER READING Choe Y H, Im J G, Park J H, Kim C W 1987 The anatomy of the pericardial space: a study in cadavers and patients. Am J Roentgenol 149: 693–697 Schoepf U J (ed) 2004 CT of the heart: Principles and applications. Humana Press, New Jersey Sharma A, Fidias P, Hayman L A, Loomis S L, Taber K H, Aquino S L 2004 Patterns of lymphadenopathy in thoracic malignancies. RadioGraphics 24: 419–434

Spindola-Franco H, Fish B G 1985 Radiology of the heart. Springer Verlag, New York Strollo D C, Rosado de Christenson M L, Jett J R 1997 Primary mediastinal tumors. Part 1: tumors of the anterior mediastinum. Chest 112: 511–522 Strollo D C, Rosado-de-Christenson M L, Jett J R 1997 Primary mediastinal tumors: part II. Tumors of the middle and posterior mediastinum. Chest 112: 1344–1357

CHAPTER

Pulmonary Infection in Adults

15

Philip C. Goodman

Specific pneumonias • Lobar pneumonias • Bronchopneumonia • Anaerobic pneumonias • Atypical pneumonia • Pulmonary tuberculosis • Nontuberculous mycobacterial disease • Fungal infections • Protozoal and metazoal diseases Pulmonary complications of HIV infection and AIDS Infections • Malignancies

The variety of infectious agents that produce pneumonia in humans is vast, encompassing bacteria, viruses, fungi, protozoa and parasites.The chest radiograph is invariably abnormal with pneumonia and when on occasion it is normal, CT of the chest may reveal underlying lung involvement. From a diagnostic standpoint radiographic findings should be combined with clinical and laboratory information to suggest the cause of infection. Differentiation of aetiologies based solely on the radiograph is not reliable, yet the pattern of abnormalities should be very useful in formulating a differential diagnosis of the nature of disease1.

SPECIFIC PNEUMONIAS Specific pneumonias are caused by organisms drawn from virtually all forms of microbial life. In the following sections the type of infections are classified in a variety of ways: their predominant appearance, by the situations in which they are acquired, and taxonomically. Some organisms cross over pattern and situational boundaries and will only be addressed briefly when that occurs. First an explanation of some terms is presented. Lobar pneumonia is usually unifocal, develops in the distal airspaces adjacent to the visceral pleura, and then spreads via collateral air drift routes to produce uniform homogeneous opacification of partial or complete segments of lung and occasionally an entire lobe. As the airways are not primarily involved and remain patent, there is little to no volume loss and air bronchograms are common. On the other hand, bronchopneumonia, frequently caused by aspiration of secretions from a colonized trachea, is usually multifocal and centred in distal airways. The process is initially heterogeneous and distributed along the course of the airways. Thus, radiologically a bronchopneumonia is characterized by large heterogeneous, scattered opacities which only later, with worsening of disease, become more homogeneous. An air bronchogram is usually absent.

The term atypical pneumonia was initially applied to the clinical and radiographic appearance of lung infection not behaving or looking like that caused by Streptococcus pneumoniae. Radiographically focal or diffuse small heterogeneous opacities are seen uniformly distributed in the involved lung. Frequently these opacities are described as reticular or reticulonodular. Community-acquired pneumonias are caused by a variety of typical and atypical organisms with a myriad of radiographic abnormalities. However, many community-acquired pneumonias are still commonly caused by Strep. pneumoniae and are lobar in appearance. Nosocomial pneumonias occur during hospitalization. They frequently appear as bronchopneumonia caused by Staphylococcus aureus and Gram-negative organisms. They may look like atypical infections, similar to those caused by Mycoplasma, viruses and Chlamydia. In practice, however, remember that radiological patterns can be indeterminate and that one infectious agent can produce many patterns2.

LOBAR PNEUMONIAS Streptococcus pneumoniae Strep. pneumoniae pneumonia (pneumococcal pneumonia) is the most common community-acquired bacterial pneumonia

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in adults. Predisposing factors include chronic illness, alcoholism, sickle-cell disease and splenectomy. Chest radiographs generally reveal a peripheral, homogeneous opacity with or without air bronchograms (Fig. 15.1).Though commonly basal and solitary, this pneumonia can occur in any lobe and may be multifocal. Round-shaped pneumonias may simulate lung masses (Fig. 15.2). Lobar volume usually remains unchanged but rarely it increases. Cavitation is very unlikely. Parapneumonic effusion is fairly common; empyema is less frequent. Atypical patterns of heterogeneous opacification have been described but are unusual. Radiographic resolution is fairly rapid with some improvement commonly seen within 1 week and total resolution within 2–6 weeks (Fig. 15.3). Failure to improve may be due to drug resistance, incorrect or inadequate antimicrobial treatment, an obstructing lesion, development

Figure 15.2 Pneumococcal pneumonia—simulates mass. A 56 year old man with fever and productive cough. (A) PA and (B) lateral chest radiographs demonstrate a discrete fairly well marginated opacity in the right lower lobe. The abnormality resolved following appropriate antibiotic therapy and Gram stains of sputum demonstrated Strep. pneumoniae. Figure 15.1 Pneumococcal pneumonia. A 38 year old man with Strep. pneumoniae pneumonia. A close-up of the PA chest radiograph demonstrates a homogeneous lingular opacity with central air bronchograms.

Figure 15.3 Pneumococcal pneumonia—resolution time. A 48 year old man with productive cough and fever. (A) AP chest radiograph demonstrates peripheral homogeneous poorly marginated opacity. (B) AP image demonstrates significant improvement 5 d after institution of therapy.

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of lung abscess or empyema, or noninfectious cause of the opacity, e.g. broncho-alveolar carcinoma3.

Klebsiella Klebsiella pneumoniae pneumonia may arise in the community or in hospital. The chest radiograph frequently demonstrates homogeneous opacity similar to Strep. pneumoniae or may reveal scattered focal heterogeneous opacities, a bronchopneumonia, as produced by other Gram-negative bacteria. Early series reported rapid cavitation of lobar consolidation often accompanied by bulging fissures signifying a very exudative response.

Legionella Legionella pneumophila causes a pneumonia (Legionnaires’ disease) which when severe has a 10–30% mortality rate. Legionnaires’ disease may be acquired in a community, nosocomial, or epidemic fashion associated with contaminated water sources. Predisposing factors include post-transplantation, chronic obstructive pulmonary disease (COPD) and heart failure. The typical radiographic patterns include solitary or multifocal, lobar pneumonia-like, homogeneous opacities, simulating Strep. pneumoniae infection4, but with a tendency to round and mass-like appearance (Fig. 15.4). Rapid progression is common, with confluence and/or spread of the initial frequently unilateral consolidation to other lobes. Cavitation has been described in immunocompromised and post renaltransplant patients. An effusion occurs in 10–35% of cases. Resolution may be quick when treated appropriately but in some instances may take weeks.

Actinomycosis Actinomycosis is caused by Actinomyces israeli, an anaerobic, Gram-positive bacterium.The organisms reside as commensals in the mouth and oropharynx and cause infection when access occurs to devitalized or previously infected tissues, particularly



PULMONARY INFECTION IN ADULTS

in the cervicofacial region and abdomen. A chronic inflammatory reaction spreads across fascial planes and causes abscesses and fistulas containing tiny sulphur granules. In fewer than one-quarter of cases the lungs are involved from aspiration or spread from abdominal or cervicofacial foci. The chest radiograph usually reveals homogeneous opacification as a lobar type pneumonia or mass5. Cavitation is common and the appearance mimics bronchogenic carcinoma. Focal fibrosis and contraction may be severe.Widespread small nodules have been reported. Pleural effusion, pleural thickening or empyema formation, and extension of disease to the contiguous soft tissue or bones (as a periostitis) set this pneumonia apart from the usual bacterial types. (Tuberculosis and nocardiosis may have a similar appearance.) At CT, scattered peripheral areas of homogeneous consolidation with central low attenuation and adjacent pleural thickening are suggestive of actinomycosis6.

Nocardiosis Nocardia asteroides is an aerobic, Gram-positive, weakly acid-fast bacillus, related to, and sometimes confused with, A. israeli and the Mycobacteria. Infections by these organisms occur worldwide, but most reported cases are from North America. The majority of affected patients are immunocompromised, including patients with acquired immune deficiency syndrome (AIDS). Nocardiosis usually begins with a focus of pulmonary infection and may disseminate to other organs, notably the brain. The chest radiographic findings vary7. Pulmonary consolidation, either unifocal or multifocal, is the usual feature and cavitation is frequent. However, many chest radiographs reveal single or multiple pulmonary nodules resembling primary lung cancer or metastatic disease (Fig. 15.5). Cavitation is common as is pleural effusion. Lymphadenopathy or chest wall involvement may be evident, especially on CT 8.

Moraxella (Branhamella) catarrhalis Moraxella catarrhalis is a Gram-negative coccus that commonly causes otitis media and sinusitis in children, and acute tracheobronchitis or a relatively mild pneumonia in older patients with COPD. Many patients have additional serious underlying disease, including bronchial carcinoma, or are taking steroids. Presentation is most common during the winter and early spring, and the most frequent radiological pattern is lobar or segmental homogeneous opacification9. Bibasal and heterogeneous or mixed heterogeneous/homogeneous opacities are also reported. Small effusions occur in one-third of patients.

Chlamydial pneumonia

Figure 15.4 Legionnaires’ disease. A 35 year old man with high fevers. The AP radiograph demonstrates homogeneous opacities in the right upper lobe. The medial one resembles a mass. Subsequent images demonstrated bilateral spread of disease determined to be caused by Legionella pneumophila.

Chlamydiae are bacteria implicated in community-acquired pneumonias. C. psittaci and C. pneumoniae (strain TWAR) cause infections in adults, and C. trachomatis largely, but not entirely, in neonates. C. psittaci causes psittacosis (ornithosis), which is usually seen following direct bird contact but occasionally after outdoor activity, e.g. mowing lawns. The clinical manifestations may be indistinguishable from an acute bacterial pneumonia. Chest radiography reveals small to large homogeneous opacities and/ or perihilar or basal reticular opacities10. Hilar nodes are occasionally enlarged and small effusions are sometimes present.

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acquired by inhalation from farm livestock or their products, and occasionally from domestic animals. Radiographic abnormalities usually consist of unilateral, but occasionally bilateral, segmental, or lobar opacities14. In 20% of patients reticular opacities are observed15. Pleural effusion occurs but is not common. Radiographic resolution occurs within 6 weeks of starting treatment. Other rickettsial infections such as Rocky Mountain spotted fever are usually tick-borne and occasionally demonstrate diffuse heterogeneous or homogeneous opacities on chest radiographs, perhaps representing vasculitis or cardiogenic pulmonary oedema16.

Francisella tularensis Francisella tularensis is a Gram-negative coccobacillus that causes tularaemia. It is endemic in parts of Europe, Asia and North America. The disease is acquired from handling infected animals, bites of insect vectors and inhalation. In patients with pleuropulmonary tularaemia the most common radiographic findings in the chest are scattered airspace consolidation, hilar adenopathy and pleural effusion17.Various other, less common, changes are seen, including cavitation.

Yersinia (Pasturella) pestis

Figure 15.5 Nocardia infection. A young immune suppressed patient presented with fever and cough. (A) PA chest radiograph demonstrates large mass with possible cavitation in the right upper lobe. (B) Single CT section demonstrates well defined large mass with central necrosis.

Yersinia pestis is a Gram-negative coccobacillus that causes plague, a disease that is endemic in parts of South America Africa and Asia. It is also found in the southwestern USA, about 20 cases being reported annually, of which 10% have respiratory involvement18. Plague exists in three forms—primary septicaemic, bubonic and pneumonic. The latter two forms are the most common and both are associated with chest radiographic changes. The principal radiographic findings are basally predominant, bilateral, multifocal areas of consolidation that rapidly progress to become confluent. Pleural effusion is common and there may be mediastinal adenopathy, the latter sometimes being the sole manifestation in the chest of the bubonic form of the disease19.

Leptospirosis The radiographic opacity characteristically clears slowly and persistent changes at 3 months are not uncommon11. C. pneumoniae (strain TWAR) causes respiratory infections in adults that are often asymptomatic or mild. It is one of the most common causes of community-acquired pneumonia. The illness may be biphasic, with initial sore throat and hoarseness followed a few weeks later by lower respiratory tract symptoms. The most common radiographic pattern in primary infection is usually unifocal and occasionally multifocal homogeneous opacity. With recurrent infection, changes are more commonly bilateral and equally homogeneous and heterogeneous. Up to one-half of patients have pleural fluid, either small or moderate in size. In one series it was not possible reliably to differentiate between pneumonia caused by C. pneumoniae and S. pneumoniae12,13.

The Leptospira interrogans complex is a group of spirochaetes pathogenic for almost all mammals, including man.The disease in humans is usually acquired from contact with contaminated water (sewage workers, water-sport participants) or directly from infected animals. Leptospirosis is a biphasic illness characterized initially by fever, headache and myalgia, followed by skin rash and renal, neurological and hepatic disorder. Pulmonary involvement, reported in 11–67% of cases, is characterized by a haemorrhagic pneumonitis. The initial radiographic pattern is often nodular (1–7-mm diameter) evolving into confluent airspace or ground-glass opacities. Changes are bilateral, commonly peripherally predominant, and resolve in about 2 weeks20. Small pleural effusions and discoid atelectasis are also described.

Rickettsial pneumonia

Other pneumonias that need to be included in a differential list of lobar type infections include primary tuberculosis (see section on mycobacterial disease), coccidioidomycosis and blastomycosis (see section on fungal disease).

The most common rickettsial lung infection is sporadic or epidemic Q-fever pneumonia caused by Coxiella burnetii, an intracellular, Gram-negative bacterium. Infection is mainly

Miscellaneous infections

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PULMONARY INFECTION IN ADULTS

BRONCHOPNEUMONIA Staphylococcus aureus Staph. aureus pneumonia occurs in debilitated hospitalized or institutionalized patients, and less frequently as a community-acquired infection. It is usually acquired by aspiration from the upper respiratory tract. Chest radiographs typically demonstrate heterogeneous opacities in a scattered multifocal and bilateral distribution21 (Fig. 15.6). Pleural effusion or empyema, and cavitation are common; air bronchograms are unusual. Pneumatoceles may form, particularly in children. Septicaemic infections, as opposed to those acquired by aspiration, cause disseminated, poorly marginated, peripheral, multifocal, nodules which can cavitate.These septic emboli are seen in drug addicts, immunocompromised patients and patients with infective endocarditis or indwelling catheters.

Gram-negative pneumonias Gram-negative pneumonias are chiefly caused by enterobacteria (Enterobacter sp., Serratia marcescens, Proteus sp, Escherichia coli, Pseudomonas aeruginosa and Haemophilus influenzae) in a hospital setting. Patients affected are invariably debilitated by a chronic medical or pulmonary disease. These bacteria are generally aspirated from a colonized upper respiratory tract or may be inhaled or spread hematogenously. The lower lobes predominantly tend to be affected and the radiographic pattern is similar to that seen with Staph. aureus infections in adults (Fig. 15.7). A CT study of Ps. aeruginosa pneumonias revealed multifocal, predominantly upper lobe, airspace consolidation, random large nodules, tree-in-bud opacities, ground-glass opacity, necrosis and pleural effusion22.

Figure 15.6 Bronchopneumonia—staphylococcus. A 24 year old man with fever and cough developed within the hospital. The AP chest radiograph demonstrates bilateral scattered homogeneous and heterogeneous opacities, some almost nodular.

Figure 15.7 Gram-negative pneumonia—septic emboli. A 52 year old man with high fevers that developed during hospitalization. AP chest radiograph demonstrates scattered peripheral discrete and rounded opacities. Right upper lobe nodule is cavitated with thin walls. Left lower lobe nodule has thick-wall cavitation. Escherichia coli was cultured from blood.

ANAEROBIC PNEUMONIAS Most anaerobic pneumonias result from aspiration of bacteria, including Bacteroides, Peptostreptococcus, microaerophilic streptococcus, and Fusobacterium following a bout of altered consciousness, or mechanical ventilation23. Immediately following aspiration the chest radiograph is frequently normal although scattered opacities representing partial atelectasis caused by aspirated food may be seen. The appearance of pneumonia is usually delayed 24–72 h, at which time heterogeneous opacities are seen in dependent lung segments (posterior upper lobe, superior, or posterobasal lower lobe.) Involvement may be uni- or bi-lateral. Empyema is a common complication, may be large, and may occur with or without radiographic evidence of pneumonia. Multiple cavities reflecting severe lung necrosis may be seen 1–3 weeks following aspiration (Fig. 15.8). Patients who delay seeking medical help for 3–4 weeks may present with a discrete lung abscess24. Nearly two-thirds of these lesions occur in the apicoposterior segments of upper lobes and the superior segments of lower lobes. These may be large, ranging in size from 2 to 12 cm. Characteristically the wall is thick and irregular. Mediastinal nodal enlargement, though not common, may be observed. The above radiological features, coupled with an indolent course and systemic symptoms, closely resemble the findings of post primary tuberculosis or bronchogenic carcinoma.

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Figure 15.8 Anaerobic pneumonia. A 51 year old man with chronic fevers and productive cough. (A) PA and (B) lateral chest radiographs demonstrate left lower lobe opacity with multiple air–fluid levels. The patient was treated for an anaerobic pneumonia and improved rapidly. Incidentally noted are right paratracheal calcified lymph nodes from prior tuberculosis or histoplasmosis.

ATYPICAL PNEUMONIA Mycoplasma pneumonia Mycoplasma pneumoniae is a major nonbacterial cause of community-acquired pneumonia in patients between the ages of 20 and 40 years. Spread is from person to person by droplets during close contact, particularly in some communities (e.g. military barracks). Symptoms resemble a viral infection with progression from the upper to the lower respiratory tract. Pneumonia occurs in less than one-tenth of those infected, is accompanied by a minimally productive cough, and usually runs a self-limiting course. Extrapulmonary complications are well described. The radiological findings are variable and may be striking in the face of minor clinical signs. The most common pattern is unilateral lower lobe involvement beginning as heterogeneous, reticular, segmental, peribronchial opacifications that may become lobar and homogeneous. Bilateral or multilobar involvement is a frequently observed variation (Fig. 15.9). Pleural effusions are uncommon. Nodal enlargement is an unusual finding in adults, occurring in about one-fifth of patients in some series11. Radiological clearing is variable and may occasionally take as long as 6 weeks. CT demonstrates ground-glass and homogeneous opacities, a bronchiolitis with centrilobular nodules, and bronchovascular thickening in approximately 80% of patients25.

Influenza A and B Influenza A and B are common causes of pneumonia in adults, particularly the elderly. Radiographic findings within a few days after symptoms begin include scattered homogeneous opacities that rapidly become bilateral, extensive and confluent. Pleural effusion is uncommon or rare. Clinical

Viral pneumonias Viral pneumonia is common in infants and children but unusual in adults. Studies of community-acquired pneumonia suggest that about 8% are viral. The pneumonia may be solely a manifestation of respiratory tract involvement (e.g. influenza) or part of a more generalized viral illness (e.g. varicella). Viral infections predispose to secondary bacterial pneumonia.

Figure 15.9 Mycoplasma pneumonia. A 35 year old man presents with nonproductive cough and fever. The PA chest radiograph demonstrates bilateral perihilar and lower lobe heterogeneous reticular opacities as well as a more focal left upper lobe homogeneous opacity. Findings are characteristic of atypical community-acquired infections.

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PULMONARY INFECTION IN ADULTS

relapse about 2 weeks after the onset of influenza may be due to secondary bacterial pneumonia (often Strep. pneumoniae or Staph. aureus). In patients with underlying haematological malignancies, chest radiographs demonstrate scattered bilateral consolidation and ill-defined nodules, and CT reveals groundglass opacities nodules and a tree-in-bud appearance26.

Herpes simplex virus (HSV)

Adenovirus

Hantavirus

Adenovirus, a common upper respiratory tract pathogen, rarely results in respiratory failure and a radiographic appearance of acute respiratory distress syndrome (ARDS)27,28. Initial radiographs show homogeneous lobar pneumonia that progresses to diffuse bilateral heterogeneous and homogeneous opacities. A similar appearance has been described in paediatric patients29.

Hantavirus is transmitted by human contact with infected deer mice and produces a pulmonary syndrome most frequently reported in the southwestern USA. Bilateral homogeneous opacities resembling ARDS are seen33 and nearly all patients have pleural fluid. The mortality rate of treated patients can approach 35%.

Infectious mononucleosis

Cytomegalovirus (CMV) pneumonia has been seen in increasing numbers with the proliferation of bone marrow and solid organ transplantation. Chest radiographs demonstrate focal and diffuse hazy opacification and multiple small (less than 5 mm) nodules, and less commonly focal consolidation34. CT reveals small centrilobar nodules and ground-glass or homogeneous consolidation generally in a symmetric and bilateral distribution35. Solitary or multiple large nodules are frequently identified at CT.

This is caused by the Ebstein–Barr virus. Radiological manifestations in the chest are uncommon and include hilar lymphadenopathy, heterogeneous opacities, small pleural effusions and lobar homogeneous consolidation30.

Varicella Varicella is unlike other viruses in that it causes pneumonia more frequently in adults than in children. Typically, young adults are affected, some predisposed to the infection by lymphoma, pregnancy, or steroid therapy. Pulmonary involvement follows the skin rash by 1–6 d. The radiological findings are characteristic, consisting of widespread 5–10 mm in diameter poorly marginated nodules or acinar opacities, which may become confluent (Fig. 15.10). The nodules usually resolve in a week or two but can persist for months (simulating metastases). CT findings are similar, including nodules and coalescing opacities; ground-glass opacities are also observed31. In resolution, numerous small irregular calcified nodules can develop; these can be evident on plain radiographs.

Figure 15.10 Varicella pneumonia. A 30 year old man with lymphoma and new development of fever and skin rash. The PA chest radiograph demonstrates bilateral poorly marginated 5–10 mm in diameter nodular opacities.

Herpes simplex virus (HSV) may also cause pneumonia characterized by hazy and homogeneous opacities seen in a segmental or subsegmental distribution, and pleural effusion in approximately 50% of patients. At CT similar findings are noted32.

Cytomegalovirus (CMV)

PULMONARY TUBERCULOSIS Mycobacterium tuberculosis accounts for more than 95% of pulmonary mycobacterial infections. Other mycobacterial species, mainly M. kansasii and the M. avium–intracellulare complex (MAC) account for the remainder. Infections are acquired via droplet inhalation from other infected individuals. In people who are previously unexposed, hypersensitivity to tuberculoprotein is absent and primary tuberculosis develops. This form is commonly seen in infants and children. With improved control of tuberculosis in western societies, however, more people reach adulthood without exposure, and primary patterns of disease are being seen with increasing frequency in adulthood. If a patient already possesses hypersensitivity to tuberculoprotein by virtue of a previous infection or BCG vaccination, then post-primary tuberculosis is seen. Should the primary disease pass into the post-primary form without a break, the term progressive primary tuberculosis is used. Factors that contribute to the large number of cases seen worldwide are human immunodeficiency virus (HIV) infection, inner city poverty, homelessness and immigration from areas with high rates of infection. Other predisposing conditions are diabetes mellitus, alcoholism, silicosis, malignancy, immune compromise from a variety of causes and living in closed institutions. Symptoms include loss of weight and appetite, malaise, fever, night sweats and cough, which may or may not be productive and accompanied by haemoptysis. Treatment is by chemotherapy and, given cooperation by the patient and a sensitive organism, it is very successful. Recourse to surgery is rare.The radiographs of patients with tuberculosis take many forms36,37, and are best discussed as primary and post-primary disease.

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Primary tuberculosis Pathologically, primary tuberculosis is characterized by macrophages, other monocytes and inflammatory fluid in an area of peripheral pneumonia. Spread of the bacilli to regional nodes and throughout the body follows within 2–6 weeks. Immunological changes in the host at this stage lead to the ability to kill the organism and healing by fibrosis, with or without subsequent calcification. Repeated episodes of arrest and progression may lead to a growing nodule, a tuberculoma. Radiographically, primary tuberculosis causes a pneumonia that is homogeneous and mimics community-acquired pneumonias, such as Strep. pneumoniae (Fig. 15.11). Any lobe may be involved; size varies from subsegmental to an entire lobe. Multifocal involvement is unusual and cavitation rare, the occurrence of the latter suggesting progressive primary disease. Compared with community-acquired pneumonia, primary tuberculosis may exhibit nodal enlargement, usually ipsilateral, hilar and/or mediastinal. In fact, lymphadenopathy is the most common manifestation of primary tuberculosis in children and occurs with or without pneumonia. In the former case, the pneumonia may sometimes obscure hilar enlargement. In adults hilar or mediastinal lymphadenopathy is less common declining to about 50% of cases in the older population. Asymmetrical bilateral hilar involvement is less commonly described38. Nodal pressure and bronchial erosion may cause segmental or lobar collapse; commonly in the anterior segment of the right upper lobe and the middle lobe. Bronchial perforation may permit endobronchial spread of disease giving rise to scattered, heterogeneous opacities mimicking a bronchopneumonia. Pleural effusion as a manifestation of primary tuberculosis occurs in children, who usually have parenchymal or nodal disease, or in teenagers and young adults, when it is frequently isolated. The effusions are often large and unilateral. Residual pleural change is unusual, pleural thickening and calcification

Figure 15.11 Primary tuberculosis. A 39 year old man with cough and fever. Homogeneous lingular opacity is noted. No definite lymphadenopathy is identified but this would not necessarily be expected in an adult.

being much more commonly due to a tuberculous empyema seen with post-primary disease. Although classically a manifestation of primary disease, miliary tuberculosis is now more commonly seen as a post-primary process in older patients. Multiple small (1–2 mm) discrete nodules are scattered evenly throughout both lungs (Fig. 15.12). Other features of primary tuberculosis may or may not be present. With therapy, the nodules clear, often rather slowly over months, leaving no residual changes. Calcification within miliary nodules is rare or nonexistent. Usually the primary pneumonia resolves completely. In one-third of patients a residual well defined rounded or irregular (linear) opacity, with or without calcification remains. This is a Ghon lesion or focus. Nodal calcification may occur in the ipsilateral hilum or mediastinum and is heterogeneous and irregular. When a Ghon lesion or focus and ipsilateral lymph node calcification are seen together the combination is termed a Ranke complex. This appearance reflects prior primary tuberculosis (Fig. 15.13). (Remember that this picture is evidence of an old infection but does not imply activity of disease. For that the clinical findings must be incorporated.)

Post-primary tuberculosis This term is used to describe tuberculosis in patients who by reason of previous infection or BCG vaccination have acquired tuberculoprotein hypersensitivity. Most cases are due to reactivation of quiescent lesions, but occasionally a new infection from an exogenous source occurs. Pathologically, the ability of the host to respond immunologically results in a greater inflammatory reaction and caseous necrosis. Radiographically, in 95% of patients the initial lesions are poorly marginated, nodular and linear opacities approximately 5–10 mm in diameter, which arise in the apicoposterior segments of an upper lobe and/or the superior segment of a lower lobe (Fig. 15.14). Isolated involvement of the anterior segment of an upper lobe with few exceptions virtually excludes the diagnosis of tuberculosis, although the anterior segment may become involved from contiguous segmental disease. Changes may be unilateral or bilateral. With progression the opacities clump together and coalesce.

Figure 15.12 Miliary tuberculosis. A 26 year old man with fevers, shortness of breath. The close-up of a PA chest radiograph demonstrates multiple, discrete 1–2 mm in diameter nodular opacities.

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Figure 15.13 Primary tuberculosis—Ghon focus, Ranke complex. A 70 year old man with a prior history of tuberculosis. The close-up of the PA chest radiograph demonstrates a right mid lung calcified nodule with ipsilateral right hilar lymph node calcification. The solitary calcified nodule is termed a Ghon focus. The combination of this with ipsilateral calcified lymph nodes is termed a Ranke complex.

Cavitation is seen in the region of abnormality in 40–80% of cases. Cavities may be single or multiple, large or small. Wall thickness varies from thin to thick. Air-fluid levels are unusual but have been recorded in up to 20% of cases (Fig. 15.15). A Rasmussen aneurysm is a rare life-threatening complication of cavitary tuberculosis caused by granulomatous weakening of a pulmonary arterial wall.



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Figure 15.15 Post-primary tuberculosis. A 53 year old man presents with night sweats and fever. A close-up of a PA chest radiograph demonstrates coalescence of poorly marginated reticular and nodular opacities in the right upper lobe with an irregularly margined moderately thick-walled cavity and small air–fluid level.

Some of the opacities calcify, though this occurs less commonly than with primary tuberculosis (Fig. 15.16). Bronchiectasis and the formation of cysts and bullae may be created by the lung distortion coupled with secondary bacterial infections. Endobronchial spread can occur with or without cavitary disease and is similar to that seen with primary tuberculosis.

Healing results in scar formation. Cavities are usually obliterated but rarely a sterile cavity remains. The fibrosis produces well defined, upper lobe nodular and linear opacities, often with evidence of severe volume loss and pleural thickening.

Pleural effusion accompanying post-primary tuberculosis is more likely an empyema which may lead to pleural thickening or calcification.

Figure 15.14 Post-primary tuberculosis. A 40 year old man presents with night sweats, nonproductive cough and fever. The chest radiograph demonstrates clumped nodular opacities, particularly in the superior segment of left lower lobe, but also in the peripheral right lung, probably in the posterior segment of the right upper lobe.

Figure 15.16 Post-primary tuberculosis. A 62 year old man with a history of tuberculosis. The chest radiograph demonstrates right upper lobe well marginated and perhaps calcified nodular opacities, as well as significant volume loss in the left upper lobe with upward retraction of the left hilum and left apical pleural thickening.

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Miliary tuberculosis now occurs more commonly as a manifestation of post-primary than of primary disease and has the same radiographic appearance as described above. If the patient goes untreated the miliary nodules get bigger but rarely more than 5 mm in diameter before death occurs. A tuberculoma may occur in the setting of primary or postprimary tuberculosis and probably represents localized parenchymal disease that alternately activates and heals.These 10–15 mm in diameter nodules are commonly single but may be multiple. The margins of the nodule are usually well defined and there may be satellite lesions nearby, though this is not a specific finding. Calcification is common. Tuberculomas frequently remain stable for years, but always carry the potential risk of activation and dissemination. Chest wall involvement may be due to haematogenous seeding or direct spread from the lung and may affect soft tissue, rib, or costal cartilage. Surgery for tuberculosis is rarely performed now but patients may still be seen and exhibit the results of phrenic nerve ablation, plombage (lucite balls or oil, inserted extrapleurally), and thoracoplasty. Several studies have looked at the value of CT in diagnosing both primary and post-primary tuberculosis39. CT can identify lymphadenopathy and parenchymal lesions not appreciated on plain radiography. Over 80% of patients have lymph nodes with low attenuation centres when contrast medium is administered. Complications or spread of tuberculosis may be better revealed by CT. However, routine use of CT would probably not be cost-effective; it is recommended when normal or equivocal radiographs are seen in association with the clinical suspicion of tuberculosis, or when complications are suspected. There is no simple answer to the frequently posed question as to whether a radiographically detected tuberculous lesion is active or not. Ill-defined coalesced nodules, poorly marginated linear opacities, and especially cavitary disease in the appropriate segments are suspicious for active disease, whereas well defined opacities are not. Exceptions occur, however, and clinical findings are necessary for the diagnosis. Stability of the radiographic appearance is comforting but it should be remembered that all tuberculous lesions, even those that strongly suggest a healed lesion, even calcified, are capable of reactivation. Resolution of abnormal opacities, decrease in cavity size, and volume loss from fibrosis all suggest a satisfactory response to treatment, with a time course in the order of weeks and months rather than days. Occasionally, during the first month of treatment, opacities will extend despite appropriate therapy. Extension of opacities or incomplete resolution on treatment should also raise the question of drug-resistant tuberculosis, failure to take the medication, or an associated bronchial neoplasm. Chest radiography may be used to screen populations for pulmonary tuberculosis and to aid in the management of known cases. Nonselective radiographic screening is still employed in some countries but has been abandoned in others

because the falling prevalence of tuberculosis has resulted in low detection rates, particularly of smear-positive cases, which, from an epidemiological point of view, are the important ones to detect. Screening is still used in some selected groups such as the military, prisons and in socio-economically disadvantaged communities. Follow-up chest radiography for known cases of tuberculosis is usually sufficient after 1, 6 and 9 months, or at the end of therapy. Long-term surveillance is no longer considered necessary in straightforward cases. This regimen may be modified if complications arise, and follow-up may be extended if there is doubt about patient compliance, if risk factors are present, or if there is severe lung damage.

NONTUBERCULOUS MYCOBACTERIAL DISEASE As mentioned above, 1−3% of pulmonary mycobacterial infections are caused by agents other than M. tuberculosis: usually M. avium–intracellulare complex (MAC ) and less commonly M. kansasii. These are free-living saprophytes, and infections are not acquired from human contacts but from the environment by inhalation or ingestion. Patients are often predisposed by reason of underlying debilitating disease, immune compromise, chronic airflow obstruction, previous pulmonary tuberculosis, or silicosis and following lung transplantation. MAC, in particular, is also seen in otherwise healthy, older women. Clinically, MAC may be an indolent process with symptoms of cough, with or without sputum production. The radiological pattern of M. kansasii is generally indistinguishable from post-primary tuberculosis40,41 and changes equivalent to primary tuberculosis are rarely described. More commonly, MAC presents with a radiological pattern that does not resemble that of post-primary tuberculosis. It consists of multiple nodules, with or without small ring opacities, showing no specific lobar predilection and bronchiectasis particularly in the lingula and right middle lobe. CT has identified a similar pattern with easier detection of bronchiectasis42,43. High-resolution CT (HRCT) demonstrates small centrilobular nodules, small airway or bronchiolar ectasia and tree-in-bud opacities (Fig. 15.17). Pleural effusion is uncommon and nodal enlargement and haematogenous spread are rare except in patients with AIDS.

FUNGAL INFECTIONS Cryptococcosis (torulosis) Cryptococcosis, also known as torulosis and European blastomycosis, is caused by inhaling spores of Cryptococcus neoformans, a fungus of worldwide distribution which is found in soil and in bird droppings. Most reports of the disease are from North America. Many patients have no symptoms and the pulmonary lesions heal spontaneously but in some the disease may spread to

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PULMONARY INFECTION IN ADULTS

Figure 15.17 Mycobacterium avium complex (MAC). An elderly woman with a long history of emphysema and chronic cough. (A) PA chest radiograph demonstrates several poorly marginated nodular opacities in the right perihilar region as well as overlying the right costophrenic angle. More coarse linear opacities emanating from the right hilum suggest the possibility of scarring or bronchiectasis. (B) Lateral radiograph demonstrates bronchiectasis in the lateral segment of the right middle lobe. (C) CT section demonstrates right middle lobe tree-in-bud opacities as well as right lower lobe mucus-filled dilated bronchi. On the lateral view a pectus excavatum is also demonstrated on lateral projection. This finding has been associated with MAC.

many organs, meningoencephalitis being the most serious consequence. Approximately half the cases of symptomatic infection are associated with immunodeficiency. The chest radiograph44,45 shows three patterns: pulmonary masses, which are usually single, but may be multiple; homogeneous segmental or lobar opacifications with or without air bronchograms, cavitation and lymphadenopathy; and diffuse nodular, occasionally military, or reticulonodular opacities. The masses usually have an ill-defined edge and may cavitate and range from approximately 5 mm to very large (Fig. 15.18). CT reveals similar findings: some ‘acinar’ nodules but no tree-in-bud abnormalities46.

Histoplasmosis Histoplasma capsulatum is a fungus found in moist soil and in bird or bat excreta in many parts of the world, but human infection is only seen with any frequency in North America, particularly in the major river valley regions of the mid and eastern USA and Canada47. Occasional epidemics of symptomatic infection (similar to the flu) are reported in areas where construction is occurring or following exposure from entering bat caves or cleaning out chicken pens; however, most cases are asymptomatic. If detected while symptomatic the chest radiograph may reveal multiple poorly-defined nodules approximately 5–10 mm in diameter (Fig. 15.19).

Figure 15.18 Cryptococcus—asymptomatic. This young man presented for routine physical examination. (A) PA chest radiograph demonstrates poorly marginated left mid lung nodular opacity. (B) Single CT section demonstrates solid left lower lobe nodule with minimal surrounding halo. Surgical resection revealed Cryptococcus infection.

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Figure 15.19 Primary histoplasmosis. A 27 year old woman with flu-like illness 2 weeks after cave exploration in Mexico. A PA chest radiograph demonstrates three or four poorly marginated nodular opacities overlying the left lower lobe. Her husband, who was suffering from similar symptoms, had identical nodules.

Less commonly a segmental or lobar pneumonia is seen. Chronic pulmonary histoplasmosis radiologically resembles post-primary tuberculosis, with upper lobe contraction, calcification and cavitation. There may be substantial adjacent pleural thickening. Hilar and mediastinal lymph nodes are frequently enlarged48. If unsuspected the disease may be diagnosed in retrospect years later by the appearance on chest radiograph of multiple calcified 3–4 mm in diameter sharplymarginated, round nodules and calcified lymph nodes in the hila and mediastinum (Fig. 15.20). Occasionally a solitary, well defined nodule may form and is then termed a histoplasmoma. When the centre of this lesion calcifies it forms a ‘target’ lesion which is very specific for this entity (Fig. 15.21). In some cases of histoplasmosis fibrosing mediastinitis may develop and can lead to constriction of mediastinal structures, including the airways, superior vena cava, pulmonary arteries and pulmonary veins. CT is helpful in demonstrating this complication.

Figure 15.20 Chronic histoplasmosis. A 55 year old man undergoing routine pre-employment physical examination. A PA chest radiograph demonstrates several well defined uniform-sized calcified nodules in both lungs with bilateral hilar and mediastinal lymph node calcification. The patient was a long-time resident of the central USA, an area endemic for histoplasmosis.

The chest radiographic manifestations are variable49. In primary coccidioidomycosis unifocal or multifocal homogeneous opacities resembling community-acquired bacterial pneumonia may be seen. Cavitation and hilar/mediastinal adenopathy may be seen with approximately 20% of these lesions (Fig. 15.22). Often the pneumonias are round and produce thin-walled cavities that can lead to a pneumothorax. Primary disease almost invariably resolves spontaneously or reveals only small residual linear or nodular scars. Chronic fibronodular cavitary disease resembling post-primary tuberculosis may also be encountered. CT demonstrates expected findings of soft tissue solitary nodule, sometimes with a low attenuation centre, cavitation, or calcification. Ground-glass halos may be seen around these nodules50. Disseminated coccidioidomycosis may cause miliary nodules.

Coccidioidomycosis Coccidioidomycosis is caused by Coccidioides immitis, a fungus which is found in soil in arid regions of the southwestern USA and northern Mexico47. Infection is acquired by inhaling dust containing the fungus. Almost half the patients develop a febrile illness; the rest are asymptomatic. The illness usually resembles a non-specific viral infection but may present with erythema nodosum, erythema multiforme and arthritis. In most instances, the disease is self-limiting, but it may progress and can even result in fatal disseminated disease, particularly in the immunocompromised patient.

Figure 15.21 Histoplasmoma. The chest radiograph obtained for left lower lobe pneumonia in a 68 year old man. The right upper lobe demonstrates central target calcification with surrounding soft tissue opacity very suggestive of histoplasmoma.

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Figure 15.22 Coccidioidomycosis. An 18 year old man with flu-like symptoms. The PA chest radiograph demonstrates homogeneous left upper lobe opacity with cavitation as well as ipsilateral hilar adenopathy.

North American blastomycosis North American blastomycosis is due to Blastomyces dermatiditis47. Pulmonary infection may be accompanied by infection of the skin, bones and genitourinary tract. Pulmonary blastomycosis is often asymptomatic.When symptoms do occur, they may be non-specific or may be those of an acute pneumonia. The chest radiograph reveals homogeneous unifocal or multifocal segmental or lobar opacification indistinguishable from acute pneumonia. Cavitation occurs in approximately 15% of cases. Sometimes, the pneumonia is spherical in shape, closely resembling bronchial carcinoma.51 Pleural thickening or pleural effusion may accompany the pneumonia in 10–15% of cases. Lymph node enlargement is infrequent. Blastomycosis may cause miliary nodules particularly in immunocompromised patients. A chronic fibrocavitary form of the disease, which resembles post-primary tuberculosis, is also seen. CT reveals pulmonary masses, consolidation, effusions and cavitation as seen on chest radiographs.



PULMONARY INFECTION IN ADULTS

of bronchial carcinoma. When considering this differential diagnosis, it should always be borne in mind that mycetomas may be difficult to see in portions of the lung that have been severely distorted by previous cavitary disease. On occasion, bleeding may be severe enough to warrant surgical resection of the lung containing the mycetoma, and bronchial artery embolization may sometimes be helpful in management. The radiological diagnosis depends on recognizing a mass within a cavity and formation of an air crescent (Fig. 15.23). Calcification within the mass is extremely rare and fluid levels are infrequent. The cavity wall and the adjacent pleura may thicken. A freely-moving fungus ball can be demonstrated on decubitus images (Fig. 15.24). The differential diagnosis of mycetoma includes blood clot or lung debris in a cavity, echinococcal disease and cavitary neoplasm. Allergic bronchopulmonary aspergillosis (ABPA) describes a hypersensitivity reaction which occurs in the major airways. It is associated with elevated serum IgE, positive serum precipitins and skin reactivity to aspergillus, and it is the most common cause of pulmonary eosinophilia in the UK. The radiographic appearances consist of: nonsegmental areas of opacity most common in the upper lobes, lobar collapse, branching thick tubular opacities due to bronchi distended with mucus and fungus, and occasionally pulmonary cavitation. Bronchial wall thickening with tramlines and ring formation indicates bronchiectasis. The lungs are often overinflated, while late in the disease there may be volume loss due to fibrosis. In chronic necrotizing (formerly semi-invasive) aspergillosis, local invasion of lung parenchyma takes place, usually in the upper lobes.This form is seen in debilitated patients and in patients with pre-existing lung damage or chronic lung disease. Thus there is some decrease in host response to the fungus. Radiographically heterogeneous opacities resembling tuberculosis are followed by an enlarging, thick-walled cavity which develops over a period of weeks. Adjacent pleural thickening

Aspergillus infection Aspergillus infections of the lung are usually caused by Aspergillus fumigatus and can take different forms depending on an individual’s immune response to the organism52. Aspergillus mycetomas are saprophytic growths which colonize a pre-existing cavity in the lung. There is relatively little invasion of the cavity wall or surrounding lung. Most cavities (e.g. from sarcoidosis or tuberculosis) and thus mycetomas are in the upper lobes or superior segments of the lower lobes. The great majority of aspergillomas are asymptomatic. Haemoptysis is the important complication. When it occurs, there may be difficulty in distinguishing between mycetoma formation, reactivation of tuberculosis and the development

Figure 15.23 Aspergilloma. A 30 year old man with a right upper lobe cavity of uncertain etiology. Within the cavity there is a rounded soft tissue opacity and superior air crescent indicative of mycetoma.

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Figure 15.24 Aspergilloma. A 60 year old man with chronic lung disease of indeterminate aetiology. Patient presents with mild haemoptysis. (A) Supine and (B) prone CT of the upper lobe demonstrate a fungus ball moving within the left upper lobe cavity.

and involvement of the chest wall may occur. Occasionally a mycetoma is observed. Bilateral involvement may occur and multiple nodules have been reported. Invasive aspergillosis is virtually confined to immunocompromised hosts. Radiologically, the appearances are variable, but a common pattern is of one or more rounded poorly marginated areas of homogeneous opacification with or without air bronchograms (Fig. 15.25). With time the margins may become more discreet and the lesions resemble masses. They may cavitate with the formation of an air crescent (Fig. 15.26). Wedge-shaped peripheral opacities, believed to be pulmonary infarcts may also be seen. Rarely, miliary nodules are observed.

Figure 15.25 Invasive aspergillosis. A 65 year old man with immunosuppression and neutropenia presents with fever. A PA chest radiograph demonstrates multiple bilateral poorly marginated nodular opacities with some coalescence of nodules in the right lower lobe.

Figure 15.26 Invasive aspergillosis. A 46 year old man on steroids and methotrexate for asthma. The patient developed cough and fever. (A) Initial chest radiograph demonstrates peripheral homogeneous opacities in both upper lobes and heterogeneous opacities in the left lower lobe. (B) A subsequent PA chest radiograph demonstrates cavitation within the peripheral left opacity following appropriate antifungal therapy and reconstitution of neutrophils 6 d into course.

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CT reveals findings as expected from chest radiography but is more sensitive and may be abnormal when radiography is normal. CT may reveal ground-glass haloes around the nodules, as may be seen in other diseases (Fig. 15.27). Optimized HRCT may permit more specific diagnoses of angio-invasive infection by actually demonstrating occlusion of the vessel supplying the focal pulmonary lesion53.

PROTOZOAL AND METAZOAL DISEASES Protozoal infections Pleuropulmonary amoebiasis caused by Entamoeba histolytica is usually secondary to liver involvement and develops in about one-fifth of such patients. It is characteristically a disease of young adults and shows a distinct male preference. Lung involvement usually occurs in the right lung base and consists of hemidiaphragmatic elevation, pleural effusion and/or thickening and plate-like atelectasis. With erosion of a liver abscess through the diaphragm, basal homogeneous opacification develops and frequently cavitates. Occasionally haematogenous spread gives rise to similar disease in other lung locations. Amoebiasis should always be considered in the appropriate clinical setting with isolated right basal radiological changes that abut the hemidiaphragm54.

Metazoal infestations With the exception of Armillifer armillatus, metazoal pulmonary disease is due to either roundworms or flatworms (tapeworms and flukes). Roundworms generally cause pulmonary consolidation with eosinophilia (acute eosinophilic pneumonia) and very occasionally an isolated pulmonary nodule (Dirofilaria immitis)55.The manifestations of flatworm infestations are more varied, and paragonimiasis and echinococcosis are considered here in detail. Two others, Taenia solium and Schistosoma sp.,

Figure 15.27 Invasive aspergillosis. A 30 year old man with neutropenia presents with fever. A chest radiograph demonstrated multiple lung nodules. This thin CT slice demonstrates heterogeneous and ground-glass opacity in the azygo-oesophageal lung recess as well as a lingular nodule consisting of an opaque centre and ground-glass halo very suggestive of invasive aspergillosis.



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can also cause radiological changes on the chest radiograph. T. solium gives rise to multiple calcified cysticerci in the chest wall muscles which appear as calcified oval opacities of 3–10 mm in diameter. Schistosoma infestation manifests as pulmonary consolidation with eosinophilia, pulmonary arterial hypertension with or without miliary nodulation or reticulonodular opacities, and slightly larger individual nodules.

Paragonimiasis Paragonimiasis is caused by a fluke (Paragonimus westermani) that develops from a larval form in the lung, where it lives, often for years, producing ova. Water snails and crustaceans are intermediate hosts and infestations are acquired from eating raw or incompletely cooked fresh water crabs and crayfish. The disease mainly occurs in the Far East, southeast Asia and Africa, and the usual presentation is with chronic cough and sputum production with haemoptysis. Radiological changes tend to be bilateral and affect any lobe (particularly the mid lung). Various abnormalities are observed including a mixture of consolidation, nodules and band, tubular and ring opacities56. Ring opacities range in size from 5 to 30 mm and may or may not be accompanied by adjacent consolidation. In some series about half the patients have had a pleural effusion. In the lower lobes parenchymal changes mimic bronchiectasis, and in the upper lobes, tuberculosis. CT may reveal peripheral linear opacities thought to be worm migration tracks56. The diagnosis is established by detecting ova in the sputum or by identifying anti-Paragonimus antibody in the blood.

Hydatid disease Hydatid disease (echinococcosis) is caused by a tapeworm, usually Echinococcus granulosus. Humans are accidental hosts and acquire infection by ingesting ova from fomites or contaminated water and by direct contact with dogs. Cysts develop in the lung, or less commonly in the mediastinum and rarely in the heart and pulmonary arteries. They are usually solitary but in one series approximately 10% of cases were multiple and/or bilateral57. CT series have demonstrated a higher percentage of multiple cysts. They may be ruptured (two-thirds) or unruptured (one-third) at the time of presentation. The radiological findings with unruptured pulmonary cysts are one or more homogeneous, roughly spherical or oval, sharply demarcated mass lesions. They range in size from 1 to 10 cm and occur particularly in the mid and lower lobes. The intrapulmonary masses are of soft tissue density and almost never calcify, unlike mediastinal lesions. Cysts are easily deformed and this leads to: lobulation or eccentricity of contour, where they come up against major bronchovascular structures; flattening of peripheral aspects in contact with the chest wall or mediastinum, in such a way that in the latter case a mediastinal mass is simulated; and changes in shape with breathing. Cyst rupture is usually associated with secondary infection and may occur into the airways or pleural space. Acute symptoms often develop and frequently precipitate presentation. There are three layers to the wall, two in the cyst itself (endo- and ecto-cyst) and a third derived from the surrounding lung (pericyst). If the two inner layers remain intact, airway

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communication results in a ring opacity containing a rounded, homogeneous density. The radiographic appearance resembles the air crescent of a mycetoma. Should there be disruption of the inner layers, a complex cavitary lesion results with one or more of the following radiographic features: an air–fluid level, a floating membrane (water lily sign, camalote sign), a double wall, an essentially dry cyst with crumpled membranes lying at its bottom (rising sun sign, serpent sign), a cyst with all its contents expectorated (empty cyst sign). Secondary infection of a

hydatid cyst may produce a lung abscess with or without surrounding lung opacity. CT can demonstrate a number of these characteristic features to better advantage than the chest radiograph58. High specificity of CT for the diagnosis of perforated pulmonary hydatid cyst (‘air bubble’ sign) has been reported59. Rupture into the pleural space causes an effusion or, if there is additional airway communication, a hydropneumothorax.The diagnosis may be established by serological testing, or examination of the sputum if there is rupture into airways.

PULMONARY COMPLICATIONS OF HIV INFECTION AND AIDS INFECTIONS The great majority of the pulmonary complications of HIV infection are infectious in origin. Of these, the three most important are Pneumocystis jiroveci (carinii) pneumonia, which is still a common disease leading to the diagnosis of AIDS; tuberculosis, which is extremely common in developing countries and is thus by far the most important (worldwide) pulmonary complication of HIV infection; and communityacquired pneumonias and airways disease. The prevalence of HIV-associated pulmonary infections varies greatly between different countries, so that it is difficult to identify them in order of importance; the clinical and radiographic features of each of the most common causative agents are considered below.

Pneumatoceles are seen in 10% of patients with Pneumocystis pneumonia and AIDS. They generally appear within a few days of the initial pneumonia, are thin walled, may rapidly increase or decrease in size, and over the course of 2–3 months

Pneumocystis jiroveci (formerly carinii) P. jiroveci, formerly carinii, was for a long time considered a parasite but has been shown to be a fungus. The widespread use of the abbreviation PCP to refer to pneumonia caused by this organism continues and will be used here. P. jiroveci is ubiquitous and is believed to infect the majority of humans early in life. It only manifests as pneumonia when immunosuppressive disorders, including AIDS, cause a profound depression of cellular immunity. The majority of HlV-infected patients who develop PCP present with fever, dyspnoea, non-productive cough, weakness and weight loss. Elevation of the serum lactase dehydrogenase (LDH) has been used as a sensitive but non-specific indicator of PCP and may have some prognostic value. The definitive diagnosis of PCP is made by demonstrating typical organisms in secretions obtained from the lungs or in lung tissue itself. The chest radiograph in most patients with Pneumocystis pneumonia demonstrates bilateral, diffuse, symmetrical, fine to medium reticular opacities. The same pattern confined to one or two lobes or segments of lung may be seen (Fig. 15.28). In some cases upper lobe predominance of infiltrates has simulated reactivation tuberculosis. Unusual radiographic presentations include diffuse or focal miliary nodules, homogeneous opacities, solitary or multiple well formed nodules and moderate to thick-walled cavitary nodules60. Approximately 5–10% of patients will have normal chest radiographs at presentation, perhaps even more frequently in less severe disease. Pleural fluid and lymphadenopathy are rare or do not occur unless extrapulmonary involvement has been observed, usually in patients who have received prophylactic aerosolized pentamidine.

Figure 15.28 Pneumocystis jiroveci pneumonia (PCP). (A) PA chest radiograph demonstrates the typical bilateral distribution of fine to medium reticular opacities. (B) A close-up of the right upper lobe of the same patient reveals the nature of this typical pattern which occasionally is confined to one lobe.

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gradually resolve61. In some cases they persist as chronic, thinwalled, air-filled cavities (Fig. 15.29). Spontaneous pneumothorax, has been observed in approximately 5% of patients with PCP (Fig. 15.30). Management is notoriously difficult, because bronchopleural fistulas are common.



PULMONARY INFECTION IN ADULTS

Significant radiographic improvement is usually seen within 10 d of beginning treatment.The radiographic appearance may get worse during the first 3 d of therapy, especially with intravenous trimethoprim–sulphamethoxazole, possibly related to overhydration pulmonary oedema and possibly to an inflammatory reaction to dead and dying parasites (Fig. 15.31). Eventually, in most patients, the pneumonia resolves completely and the chest radiograph becomes normal, though in some, pulmonary fibrosis develops. The value of CT in PCP diagnosis is questionable given the cost of imaging but it has been used to differentiate between pneumonias and to exclude the diagnosis62. CT demonstrates unilateral or bilateral ground-glass or homogeneous opacities in geographical distribution. The possibility of recurrence of PCP due to immune reconstitution following retroviral therapy has been reported63.

Mycobacterium tuberculosis In the USA tuberculosis has occurred in approximately 4% of all patients with AIDS, but in sub-Saharan Africa, where millions of people are co-infected with HIV and tubercle bacilli,

Figure 15.29 Pneumocystis jiroveci pneumonia (PCP). (A) A close-up of the right upper lobe demonstrates medium reticular opacities. (B) This close-up of the right upper lobe was obtained 3 weeks after (A). The lung disease has resolved but a thin-walled pneumatocele 30 mm in diameter is now demonstrated (arrows).

Figure 15.30 Pneumocystis jiroveci pneumonia (PCP). An AP chest radiograph demonstrates a large right tension pneumothorax. Severe underlying bilateral pneumocystis pneumonia was diagnosed. What probably represents a large left upper lobe pneumatocele is also noted.

Figure 15.31 Pneumocystis jiroveci pneumonia (PCP). (A) AP chest radiograph demonstrates a mild, diffuse reticular pattern typical of P. jiroveci infection. (B) On the fourth day of trimethoprim– sulphamethoxazole therapy the chest radiograph demonstrates a worse, coarse, bilateral reticular pattern. Following diuretic therapy the radiographic appearance quickly returned to baseline.

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tuberculosis has become the most common and most important manifestation of AIDS. Worldwide, tuberculosis is the most common cause of death among AIDS patients. Clinical features depend on the stage of HIV-induced immunosuppression at the time that tuberculosis is encountered. Tuberculosis may be indistinguishable from ‘ordinary’ disease in patients whose HIV infection is at an early stage and whose cellular immunity is better preserved. Cutaneous reactivity to tuberculin is present, the chest radiograph is typical, and extrapulmonary disease occurs with the same frequency (15–20%) as it does in patients not infected with HIV. However, when tuberculosis develops in the late stages of HIV disease, patients often have a negative tuberculin skin test reaction; more than half will have extrapulmonary (especially lymph node) involvement; and the chest radiographs are usually atypical. The diagnosis of tuberculosis rests on isolation and identification of M. tuberculosis. Antituberculous chemotherapy is usually started with three or four drugs, including isoniazid, rifampicin and pyrazinamide, with ethambutol and or other drugs added when there is a possibility of drug resistance. Longer courses of treatment than usual have been recommended. In patients with early HIV disease and limited immunosuppression the chest radiograph is similar to that seen in the general population. Homogeneous segmental or lobar opacification mimicking Strep. pneumoniae is observed with or without ipsilateral hilar and/or mediastinal adenopathy. Alternatively the post-primary type of disease with upper lobe clumped nodular or coalesced coarse reticulonodular opacities with or without cavitation may be noted. However, with advanced HIV-induced immunosuppression, diffuse bilateral coarse reticulonodular opacities are typically demonstrated. The pattern is commonly distinctive enough to suggest that an infection other than Pneumocystis pneumonia is present. Hilar and/or mediastinal adenopathy is well documented, as is a mid or lower lobe predominance of lesions (Fig. 15.32). Cavitation is not expected in this setting64. A high prevalence of pleural effusion was observed in some HIV-infected patients with tuberculosis, but this has not been universally observed.With effective antituberculosis therapy, the majority of patients will demonstrate both clinical and radiographic improvement within 1–2 weeks. In comparison, if the radiographic appearances deteriorate, a second disease process or possibly infection with a drug-resistant strain of M. tuberculosis warrants consideration65. The use of highly active antiretroviral therapy (HAART) may lead to increasing mediastinal adenopathy and worsening or new lung opacities due to a systemic inflammatory response resulting from immune reconstitution66.

Mycobacterium avium complex Mycobacterium avium complex (MAC), a ubiquitous microorganism that is found in house dust, soil and water, may cause complications for patients with end-stage HIV infection but has decreased in incidence as antiretroviral regimens have been administered. The role of MAC in causing pulmonary abnormalities should be taken seriously since disseminated MAC infection decreases life expectancy. There are no distinctive chest radiographic abnormalities in patients with MAC infection and AIDS;67 moreover, other

Figure 15.32 Tuberculosis. A PA chest radiograph demonstrates a diffuse, bilateral coarse nodular pattern associated with right hilar adenopathy. This combination of findings should suggest the presence of fungal or mycobacterial disease.

associated opportunistic diseases are common. Among patients with MAC, diffuse bilateral opacities, focal consolidation, pleural fluid, adenopathy and normal radiographs have been reported. Cavitation is rare. Considerable overlap has been found in the CT findings of nontuberculous mycobacterial infection and tuberculosis. Both demonstrate centrilobular nodules, some ground-glass attenuation and lymphadenopathy68.

Other nontuberculous mycobacteria Virtually all nontuberculous mycobacterial disease in AIDS patients is caused by MAC, but M. kansasii, M. gordonae, M. fortuitum and M. chelonei have also been implicated. The radiographic features of these agents in AIDS patients are variable and include diffuse infiltrates, focal infiltrates, cavitation, heterogeneous and homogeneous opacities predominantly in the upper lobes, lymphadenopathy and pleural effusions69,70.

Pyogenic organisms Community-acquired pneumonias, especially Strep. pneumoniae and Haemophilus influenzae, are common in HIV-infected patients. Patients with HIV infection also develop pneumonias related to their cell-mediated immune deficiencies from organisms such as Nocardia asteroides, Salmonella sp. and Legionella sp. Infections with Staph. aureus, Moraxella, Branhamella catarrhalis, Rhodococcus equi and M. pneumoniae are also reported. The clinical presentation of HIV-related Strep. pneumoniae or H. influenzae pneumonia is indistinguishable from that seen in the normal host, and is characterized by the sudden onset of high fever and a productive cough71. The radiographic features of pyogenic bacterial pneumonia in patients with AIDS are similar to those seen in non-immunosuppressed individuals. Chest radiographs demonstrate focal or multiple areas of lobar homogeneous opacification72 and, occasionally, pleural effusion (Fig. 15.33). Bronchitis and bron-

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empyema are also seen. This aetiology should be considered when cavitary pneumonias are observed in HIV patients with low CD4 lymphocyte counts. CT reveals mediastinal lymph node enlargement simulating lymphoma74.

Cytomegalovirus

Figure 15.33 Streptococcal pneumoniae pneumonia. An AP radiograph demonstrates homogeneous opacification of the right lower lobe. This pattern of pyogenic bacterial pneumonia in AIDS patients is no different from that seen in nonimmunosuppressed individuals.

chiectasis may develop acutely or may be a sequel of recurrent pyogenic pneumonias in patients with AIDS. The abnormalities on plain radiographs include peribronchial thickening and ‘tram tracking’. On CT, dilated bronchi and peribronchial thickening with or without mucous plugs are observed73. Airways disease may also result from other infectious or noninfectious aetiologies including lymphocytic interstitial pneumonia (LIP), PCP and tuberculosis. Pulmonary nocardiosis presents with cavitation, abscesses, mixed heterogeneous and homogeneous patterns and pleural fluid. Rhodococcus equi may cause necrotizing pneumonia. Patients present with chest pain, fever, productive cough and haemoptysis. Chest radiographs demonstrate homogeneous opacity frequently with cavitation (Fig. 15.34). Pleural effusions and

Cytomegalovirus pneumonia is well documented in immunocompromised patients, especially after bone marrow, kidney, lung, or heart transplantation. However, its role in respect to pneumonia in patients with AIDS is problematical due to superimposed infections and difficulty in establishing the diagnosis. Cytomegalovirus can be isolated from respiratory secretions or lung tissue in one-quarter to one-third of patients with AIDS-related lung diseases, especially PCP. In this setting it is impossible to identify what contribution, if any, the virus is making to the clinical and radiographic features of the patient’s pulmonary disorder. The principal chest radiographic abnormality of suspected cytomegalovirus pneumonia in patients with AIDS is a bilateral fine reticular pattern, similar to that seen with PCP. An analysis of 21 patients with AIDS and cytopathological evidence of cytomegalovirus infection revealed chest CT abnormalities, including ground-glass opacities and dense consolidation, bronchial wall thickening, heterogeneous densities and discrete nodules75.

Cryptococcus neoformans The usual disease caused by Cryptococcus neoformans in patients with HIV infection is meningitis, but about one-third of these patients have simultaneous pulmonary involvement and present with respiratory symptoms. Patients with cryptococcal pneumonia typically present with weight loss, fever, productive cough and breathlessness. The definitive diagnosis is usually made by cytology and culture of induced sputum or broncho-alveolar lavage fluid. When cryptococcal lung disease is found, the patient should be evaluated for meningeal involvement. The most common chest radiographic manifestation is diffuse reticular opacification. However involvement may be limited to one lung or lobe and focal homogeneous opacity, pleural effusion, hilar adenopathy, and cavitation have all been described (Fig. 15.35). CT may provide additional information76.

Histoplasma capsulatum

Figure 15.34 Rhodococcus equi. A 22 year old man with fever and cough. A PA chest radiograph demonstrates a thick-walled cavity adjacent to heterogeneous opacities in the right upper lobe. Necrotizing pneumonias are typical with this organism.

Cases of AIDS-related progressive disseminated histoplasmosis have been recognized in endemic regions of the USA. The same phenomenon may occur in endemic areas of Central and South America and elsewhere. Progressive systemic disease produces prominent weight loss and prolonged fever. Cough and dyspnoea are common in patients with chest radiographic abnormalities.The diagnosis is usually made by the biopsy and culture of bone marrow or blood. The radiographic features of histoplasmosis in patients with AIDS include normal chest radiographs in 50% of AIDS patients with extrapulmonary histoplasmosis, nodular or linear opacities in 50%, nearly 20% with pleural effusions, and approximately 10% with lymphadenopathy77 (Fig. 15.36).The lung abnormalities may be coarse and nodular, thus distinguishable from the

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Figure 15.35 Cryptococcus. An AP chest radiograph demonstrates a fine reticular pattern, right paratracheal and hilar adenopathy, and left pleural fluid. Although the pattern may simulate that seen with PCP, the presence of adenopathy and pleural fluid should direct attention towards another diagnosis.

fine reticular pattern seen with PCP. The presence of lymphadenopathy would also distinguish histoplasmosis from PCP.

Figure 15.37 Coccidioidomycosis. A close-up of a PA chest radiograph demonstrates coarse reticulonodular opacities typical of disseminated fungal or mycobacterial disease in AIDS patients. The possibility of left hilar adenopathy is raised.

Coccidioides immitis

Aspergillosis

Coccidioidomycosis, in AIDS patients may be seen in the endemic areas of the southwestern USA. Fever, weight loss, cough and fatigue are usually present in patients with AIDS-related disseminated coccidioidomycosis. Spherules can usually be identified in sputum and fungal cultures from broncho-alveolar lavage, or transbronchial biopsy are likely to be positive. Diffuse, medium to coarse nodular opacities similar to those seen with histoplasmosis and with disseminated tuberculosis were seen in 55% of patients; 36% had focal abnormalities, including single or multiple nodules, cavities and hilar and mediastinal adenopathy78 (Fig. 15.37).

Despite its importance as a complication of other immunosuppressive disorders, especially leukaemia and organ transplantation, aspergillosis is relatively infrequent in patients with HIV-induced immune deficiency. Two types of HIV-associated aspergillosis have been observed: invasive pulmonary aspergillosis, which is characterized by prolonged cough and fever; and obstructing bronchial aspergillosis, which is characterized by breathlessness, cough and chest pain. The radiographic features of aspergillosis in patients with AIDS include focal and occasionally persistent homogeneous opacities. These may remain stable for several months but are indicative of invasive aspergillosis. Approximately one-third of patients demonstrate cavitation, chiefly in upper lobe homogeneous opacities. Disseminated heterogeneous and homogeneous patterns are observed with widespread disease. CT may reveal nodules with surrounding ground-glass halos, or airway disease manifest by centrilobular nodules and peribronchial opacities79.

Protozoal diseases Toxoplasma gondii

Figure 15.36 Histoplasmosis. A PA chest radiograph demonstrates the typical findings of histoplasmosis in AIDS patients. A pattern composed of small nodules 2–4 mm in diameter is seen in both lungs.

Judging from serological studies, Toxoplasma gondii is a prevalent infection (40–60%) in the general population. Reactivation of central nervous system (CNS) toxoplasmosis is a common cause of seizures, focal neurological deficits and/or encephalopathy in patients with AIDS. In view of the frequency of CNS toxoplasmosis, pulmonary involvement is surprisingly unusual, though it may occur and progress to respiratory failure. Chest radiographs in the few reported patients demonstrate bilateral lower lobe homogeneous opacities, a solitary nodule and bilateral diffuse heterogeneous opacities. In our series, bilateral coarse nodular opacities were the most common

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Kaposi’s sarcoma

Kerley B lines are occasionally present. The lung abnormalities tend to coalesce together unlike the nodules seen with lymphoma82. Unilateral or bilateral pleural fluid is reported in 33–50% of patients and lymphadenopathy has been observed in 10–30% (Fig. 15.39). Rapid progression from a poorlydefined nodular pattern to one of airspace consolidation has usually been seen in patients with haemoptysis, and probably represents haemorrhage into the lung (Fig. 15.40). Unusual radiographic features of KS include pericardial fluid accumulation due to pericardial KS and the plain chest

At the beginning of the AIDS epidemic, Kaposi’s sarcoma (KS) was the indicator disease in 20–25% of all cases but its incidence has fallen considerably81. KS is caused by the human herpes virus 8 (HHV8). Most patients with KS present with one or more typical violaceous plaques on their skin or mucous membranes. Primary involvement of visceral organs may also occur, particularly in the gastrointestinal tract; other sites include lymph nodes, liver, spleen, heart and pericardium. Primary pulmonary KS is unusual. Most cases of pulmonary KS occur in the presence of obvious disease in the skin or elsewhere. The manifestations of pulmonary KS are fever, cough and breathlessness, and thus are indistinguishable from those of many pneumonias. Haemoptysis and upper airway obstruction rarely occur. Dyspnoea from effusions may require treatment. Compared with the non-specific radiographic abnormalities observed with the opportunistic pulmonary infections discussed above, the findings of KS are more specific and the diagnosis may sometimes be suggested on the basis of the chest radiograph and CT abnormalities.The usual pattern is a poorly defined peribronchovascular nodular opacity which typically measures 10–20 mm in diameter. Although solitary nodular KS may occur, bilateral multiple lesions are typically present. Coarse linear opacities are also commonly scattered throughout the lungs, particularly in the perihilar and lower lungs and

Figure 15.39 Kaposi’s sarcoma. A PA chest radiograph demonstrates coarse linear opacities in the perihilar regions. Some nodular opacities are noted in the right upper lobe. Left pleural fluid is present. This constellation of findings is highly suggestive of Kaposi’s sarcoma.

Figure 15.38 Toxoplasmosis. A close-up of a portable AP chest radiograph demonstrates a coarse nodular pattern which was present in the perihilar and lower lobe regions of the lung.

Figure 15.40 Kaposi’s sarcoma. Fairly large, coarse nodules are noted in the right upper lobe and left lung. An area of homogeneous opacification in the right middle lobe appeared at the same time as this patient developed haemoptysis. This radiographic abnormality probably represents haemorrhage in the lung.

pattern; lymphadenopathy was not observed and pleural effusion was uncommon80 (Fig. 15.38).

MALIGNANCIES Some malignancies have close association with infectious agents, and as they may mimic infection they are included here.

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diffuse parenchymal opacities, pleural fluid and rapidlygrowing well defined parenchymal nodules (Fig. 15.41). These nodules range in size from 10 to 60 mm, may be solitary or multiple and only rarely cavitate. CT may reveal similar findings and would be expected to be more sensitive than chest radiography.

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Figure 15.41 Non-Hodgkin’s lymphoma. (A) A close-up of a PA chest radiograph demonstrates a fairly well defined nodule, 15 mm in diameter, in the left upper lobe. (B) A close-up of the chest radiograph obtained 10 d later demonstrates considerable enlargement of the nodule which, on open lung biopsy, was shown to represent non-Hodgkin’s lymphoma.

radiographic demonstration of a large intratracheal Kaposi’s lesion. Endobronchial lesions may cause complete occlusion of airways. Occasionally septic emboli in intravenous drug abusers with AIDS may simulate KS. In this situation cavitation would be expected, whereas cavitation in KS is rare or not observed.

Non-Hodgkin’s lymphoma Although intrathoracic involvement by non-Hodgkin’s lymphoma in patients with AIDS is not common, when lesions occur they include: hilar and/or mediastinal adenopathy,

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CHAPTER

Large Airway Disease and Chronic Airway Obstruction

16

Philippe Grenier

• • • • • • •

Tracheal disorders Bronchiectasis Broncholithiasis Emphysema Chronic bronchitis Asthma Obliterative (constrictive) bronchiolitis

This chapter reviews lesions involving the trachea and proximal bronchi, describes the radiological signs of bronchiectasis, and discusses the role of imaging in obstructive lung disease, a group of diffuse lung diseases associated with chronic airflow obstruction that includes chronic obstructive pulmonary disease (COPD), asthma and obliterative bronchiolitis. In obstructive lung disease, decreased expiratory flow may be related to loss of lung recoil or small airway obstruction or a combination of both. The pathological lesion that best correlates with loss of recoil is emphysema. The process that causes the small airway obstruction is inflammatory in nature and is characterized by thickening of all the layers of the bronchiolar walls, as well as an accumulation of mucus in the airway lumen (COPD and asthma) and/or an irreversible fibrosis (obliterative bronchiolitis).

TRACHEAL DISORDERS1–4 The trachea may be affected by a variety of extrinsic or intrinsic processes. Extrinsic processes, particularly masses, displace and distort the trachea, while intrinsic ones cause narrowing, widening, or a mass effect.Tracheal narrowing may affect a short or a long segment, and may extend to the mainstem bronchi. Tracheal disease initially missed on the chest radiograph is usually evident on careful evaluation of the frontal and lateral radiograph5. Computed tomography (CT) allows precise delineation of the intratracheal and extratracheal extent of the abnormality. Multidetector CT (MDCT), by combining helical volumetric CT acquisition and thin collimation during a single breath-

hold, provides an accurate assessment of the proximal airways, allowing multiplanar reformations and three-dimensional (3D) rendering of very high quality. Complementary CT acquisition at suspended or continuous expiration allows tracheal collapsibility to be assessed.

Post-traumatic strictures Strictures of the trachea are usually secondary to damage from a cuffed endotracheal or tracheostomy tube, or to external neck trauma.The lesions consist of granulation tissue followed by the development of dense mucosal and submucosal fibrosis associated with distortion of cartilage plates. The two principal sites of stenosis following intubation or the insertion of a tracheostomy tube are at the stoma or at the level of the endotracheal or tracheostomy tube balloon. On radiographs, the stenosis may be seen as a focus of circumferential or eccentric narrowing associated with a segment of increased soft tissue. The size of narrowing is usually clearly seen on CT.The narrowing is often concentric. Postintubation stenosis extends for several centimetres and typically involves the trachea above the level of the thoracic inlet. Post-tracheostomy stenosis typically begins 1–1.5 cm distal of the inferior margin of the tracheostomy stoma and involves 1.5–2.5 cm of tracheal wall. Multiplanar reformations are particularly helpful in defining accurately the site, length and degree of the stenosis. In selected cases, the degree of stenosis may also be defined by use of virtual bronchoscopy.

Infectious tracheobronchitis A number of infections, both acute and chronic, may affect the trachea and proximal bronchi, resulting in both focal and diffuse airway disease. Subsequent fibrosis may result in localized airway narrowing. The most common causes of infectious tracheobronchitis are bacterial tracheitis in immunocompromised patients, tuberculosis, rhinoscleroma (Klebsiella rhinoscleromatis) and necrotizing invasive aspergillosis. On CT, the extent of irregular and circumferential tracheobronchial narrowing is clearly demonstrated, and in some patients an accompanying mediastinitis (opacification of the mediastinal fat) is evident.

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In active disease, the narrowed trachea and frequently one or other main bronchus have an irregularly thickened wall. In the fibrotic or healed phase, the trachea is narrowed but has a smooth wall of normal thickness.

Primary malignant neoplasms These are uncommon, accounting for less than 1% of all thoracic malignancies. The vast majority are squamous cell carcinoma and adenoid cystic carcinoma. Other neoplasms, such as mucoepidermoid carcinoma, carcinoid tumour, lymphoma, plasmacytoma and adenocarcinoma are rare. On CT, they appear as a soft tissue mass, most often in the posterior and lateral wall (Fig. 16.1A). Often sessile and eccentric, resulting in asymmetrical luminal narrowing, rarely they may appear circumferential. They can be polypoid and are mostly intraluminal with mediastinal extension in 30–40%. The surface of the tumour is often irregular in squamous cell carcinoma, whereas it is smooth in adenoid cystic carcinoma. Multiplanar reformation and volumetric rendering images are recommended for a precise pre-therapeutic assessment of tumour extent (Fig. 16.1B). The tumours are best treated surgically, especially with primary resection and re-anastomosis followed by radiation.

Secondary malignant neoplasms The large airways may be involved secondarily by malignant neoplasms as a result of either haematogeneous metastasis or direct invasion from the oesophagus, thyroid, mediastinum, or lung. Neoplasms that have a propensity to metastasize to the trachea and major bronchi include renal cell carcinoma and melanoma. On CT the abnormalities are usually focal and include intraluminal soft tissue nodules and wall thickening.

Benign neoplasms The most common benign neoplasms are hamartoma, leiomyoma, neurogenic tumour and lipoma. They are usually well demarcated, round and less than 2 cm in diameter. The radiological appearance typically consists of a smoothly marginated intraluminal polyp. Hamartomas and lipomas may demonstrate fat attenuation on CT. Tracheobronchial papillomatosis is a particular entity caused by human papillomavirus infection usually acquired at birth from an infected mother. The larynx is affected most commonly; extension into the trachea and proximal bronchi occurs occasionally. Exceptionally the infection spreads into the lung parenchyma. The typical radiological findings consist of multiple small nodules projecting into the airway lumen or diffuse nodular thickening of the airway wall. Although benign, papilloma may undergo transformation to squamous cell carcinoma.

Wegener’s granulomatosis Involvement of the large airways is a common manifestation of Wegener’s granulomatosis. Inflammatory lesions may be present with or without subglottic or bronchial stenosis, ulcerations and pseudotumours. Radiological manifestations include thickening of the subglottic region and proximal trachea with a smooth symmetrical or asymmetrical narrowing over a vari-

Figure 16.1 Adenoid cystic carcinoma of the trachea. (A) Axial CT at the level of the supra-aortic part of the mediastinum. Irregular stenosis of the tracheal lumen due to a soft tissue mass developing from the posterior and left lateral wall of the trachea. (B) 3D external volume rendering of the airways in a coronal view. The level of the tracheal lumen involvement (arrow) is accurately assessed with respect to the larynx and carina. The length and the degree of the stenosis are also clearly seen.

able length. Stenosis may also be seen on any main lobar or segmental bronchus. Nodular or polypoid lesions may also be seen on the inner contour of the airway lumen.

Relapsing polychondritis This is a rare systemic disease of autoimmune pathogenesis that affects cartilage at various sites, including the ears, nose, joints and tracheobronchial tree. Histologically, the acute inflammatory infiltrate present in the cartilage and perichondrial tissue induces progressive dissolution and fragmentation of the cartilage followed by fibrosis. Symmetrical subglottic stenosis is the most frequent manifestation in the chest (Fig. 16.2A). As the disease progresses, the distal trachea and bronchi may be involved. CT shows smooth thickening of the airway wall associated with more or less diffuse narrowing (Fig. 16.2B). In the early stage, the posterior wall of the trachea is spared

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Figure 16.2 Relapsing polychondritis. (A) PA chest radiograph targeted on the upper and mid parts of the mediastinum. The upper part of the tracheal lumen is narrowed (black arrows). The right paratracheal band is abnormally thickened (white arrows). (B) Axial CT at the level of the aortic arch showing abnormal thickening of the anterior and lateral walls of the trachea associated with calcium deposits (arrow). The posterior membranous wall of the trachea is unaffected.

but in advanced disease circumferential wall thickening occurs. The trachea may become flaccid with considerable collapse at expiration. Gross destruction of the cartilaginous rings with fibrosis may cause stenosis.

Amyloidosis Deposition of amyloid in the trachea and bronchi may be seen in association with systemic amyloidosis or as an isolated manifestation. As a result, the amyloid forms either multifocal or diffuse submucosal plaques or masses.The overlying mucosa is usually intact. Dystrophic calcification or ossification is frequently present. CT shows focal or, more commonly, diffuse thickening of the airway wall and narrowing of the lumen. Calcification may be seen. Narrowing of the proximal bronchi can lead to distal atelectasis, bronchiectasis, or obstructive pneumonia.

Tracheobronchopathia osteochondroplastica This rare disorder is characterized by the presence of multiple cartilaginous nodules and bony submucosal nodules on the inner surface of the trachea and proximal airways. Men are more frequently affected than women and most patients are older than 50. Histologically, the nodules contain heterotopic bone, cartilage and calcified acellular protein matrix. The overlying bronchial mucosa is normal and because it contains no cartilage, the posterior wall of the trachea is spared. The chest radiograph may be normal or may demonstrate lobar collapse or infective consolidation. If the tracheal air column is clearly seen, multiple sessile nodules that project into the tracheal lumen extending over a long segment of the trachea can be appreciated. On CT tracheal cartilage rings are thickened and shows irregular calcifications. The

nodules may protrude from the anterior and lateral walls into the lumen; they usually show foci of calcification.

Sabre-sheath trachea6 Characterized by a diffuse narrowing involving the intrathoracic trachea, this entity is almost always associated with COPD.The pathogenesis of the lesion is obscure, but probably it is an acquired deformity related to the abnormal pattern and magnitude of intrathoracic pressure changes in COPD. On radiographs and CT, the condition is easily recognized by noting that the internal side-to-side diameter of the trachea is halved or less than the corresponding sagittal diameter (Fig. 16.3A). On the postero-anterior (PA) radiograph and CT multiplanar reformations (Fig. 16.3B), the narrowing usually affects the whole intrathoracic trachea, with an abrupt return to normal calibre at the thoracic inlet. The trachea usually shows a smooth inner margin but occasionally has a nodular contour. Calcification of the tracheal cartilage rings is frequently evident.

Tracheobronchomegaly (Mounier–Kuhn disease) Tracheobronchomegaly refers to patients who have marked dilatation of the trachea and mainstem bronchi. It is often associated with tracheal diverticulosis, recurrent lower respiratory tract infection and bronchiectasis. Atrophy affects the elastic and muscular elements of both the cartilaginous and membranous parts of the trachea. The diagnosis is based on radiological findings. The immediately subglottic trachea has a normal diameter, but it expands as it passes to the carina and this dilatation often continues into the major bronchi. Atrophic mucosa prolapses between cartilage rings and gives the trachea a characteristically corrugated outline on a plain

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Figure 16.3 Sabre-sheath trachea in a patient with chronic obstructive pulmonary disease. (A) Axial CT at the level of the upper lobes shows a significant reduction of the coronal diameter of the trachea. Bilateral centrilobular and paraseptal emphysematous areas are also present in the upper lobes. (B) Coronal oblique reformation along the long axis of the trachea. Reduction of the coronal diameter of the tracheal lumen (arrows). The upper part of the trachea above the thoracic inlet has a normal appearance.

radiograph. Corrugations may become exaggerated to form sacculations or diverticula. On CT a tracheal diameter of greater than 3 cm (measured 2 cm above the aortic arch) and diameters of 2.4 and 2.3 cm for the right and left bronchi, respectively, are diagnostic criteria (Fig. 16.4A). Additional findings include tracheal scalloping (Fig. 16.4B) and diverticula (especially along the posterior membranous tracheal wall).

Tracheobronchomalacia6 This abnormality results from weakened tracheal cartilage rings and is seen in association with a number of disorders, including tracheobronchomegaly, COPD, diffuse tracheal inflammation such as relapsing polychondritis, as well as following trauma. On radiographs, an almost 300% reduction in the sagittal diameter at expiration is an excellent

Figure 16.4 Tracheobronchomegaly in a patient with bilateral bronchiectasis and recurrent pulmonary infections. (A) Axial CT at the level of the upper part of the chest shows the dilated irregular lumen of the trachea. There is bilateral cylindrical and varicose bronchiectasis in the upper lobes. (B) 3D external volume rendering of the airways showing irregular dilatation of both trachea and main bronchi. Dilatation is also present in the lobar bronchi. In addition, the trachea is irregular in contour with multiple corrugations. (Reprinted from “Imagerie Thoracique de l’ Adulte” 3rd. ed., 2006, Flammarion, with permission).

diagnostic indicator. On CT, diagnosis is based on a narrowing of the diameter of the lumen by more than 50% on expiration compared with that on inspiration. The increase in compliance is due to the loss of integrity of the wall’s structural components and is particularly associated with damaged or destroyed cartilage. The coronal diameter of the trachea becomes significantly larger than the sagittal one, producing a lunate configuration. The flaccidity of the trachea or bronchi is usually most apparent during coughing or forced expiration. In patients with COPD with high downstream resistance particularly high dynamic pressure gradients can be generated across the tracheal wall, and it is likely that calibre changes of more than 50% can occur at expiration with normal tracheal compliance. As a result only a decrease in the cross-sectional area of the tracheal

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lumen of greater than 70% at expiration indicates tracheomalacia. Dynamic expiratory MDCT may offer a feasible alternative to bronchoscopy in patients with suspected tracheobronchomalacia7. Dynamic expiratory CT may show collapse of the more than 75% of the airway lumen; indeed, complete collapse may be seen (Fig. 16.5). Involvement of the central tracheobronchial tree may be diffuse or focal. The reduction of the airway may have an oval or crescentic shape.The crescentic form is due to the bowing of posterior membranous trachea.

Tracheobronchial fistula and dehiscence8 MDCT with thin collimation is the most accurate technique to identify peripheral bronchopleural fistulas, which are most commonly caused by necrotizing pneumonia or secondary to traumatic lesions. Nodobronchial and nodobronchoesophageal fistulas, which are most commonly caused by Mycobacterium tuberculosis infection, are characterized by the presence of gas in cavitated hila or mediastinal lymphadenopathy adjacent to the airways. Tracheal diverticula and tracheobronchoesophageal fistulas may also be diagnosed, even in adults. Malignant neoplasia, particularly oesophageal, are the most common cause of tracheo-oesophageal fistulas in adults. Occasionally congenital fistulas first manifest in adults. Infection and trauma are the most frequent nonmalignant causes. MDCT has a high degree of sensitivity and specificity for depicting bronchial dehiscence occurring after lung transplantation. Bronchial dehiscence is seen as a bronchial wall defect associated with extraluminal air collections.

BRONCHIECTASIS1,3,4 Bronchiectasis is a chronic condition characterized by local, irreversible dilatation of bronchi, usually associated with inflammation. In spite of its decreased prevalence in developed countries, bronchiectasis remains an important cause of haemoptysis and chronic sputum production. Although the causes of bronchiectasis are numerous, there are three mechanisms by which the dilatation can develop: bronchial obstruction, bronchial wall



LARGE AIRWAY DISEASE AND CHRONIC AIRWAY OBSTRUCTION

damage, and parenchymal fibrosis (Table 16.1). In the first two mechanisms, the common factor is the combination of mucus plugging and bacterial colonization. Cytokines and enzymes released by inflammatory cells plus toxins from the bacteria result in a vicious cycle of increasing airway wall damage, mucous retention and bacterial proliferation. In parenchymal fibrosis, the dilatation of bronchi is caused by maturation and retraction of fibrous tissue located in the parenchyma adjacent to an airway (traction bronchiectasis). Pathologically, bronchiectasis has been classified into three subtypes, reflecting increasing severity of disease: cylindrical, characterized by relatively uniform airway dilatation; varicose, characterized by nonuniform and somewhat serpiginous dilatation; and cystic. As the extent and degree of airway dilatation increase, the lung parenchyma distal to the affected airway shows increasing collapse from fibrosis.

Radiographic findings Chest radiography reveals abnormalities in the majority of cases (Figs 16.6 and 16.7). Thickened bronchial walls are visible either as single thin lines or as parallel line opacities (tramlines). When seen end-on, bronchiectatic airways appear as poorly defined ring or curvilinear opacities (Fig. 16.6B). Dilated bronchi filled with mucous or pus result in tubular or ovoid opacities of variable size. Cystic bronchiectasis manifests as multiple thin-walled ring shadows often containing air–fluid levels (Fig. 16.7). Pulmonary vessels may appear increased in size and may be indistinct because of adjacent peribronchial inflammation fibrosis. In generalized bronchiectasis, such as that associated with cystic fibrosis, overinflation is often present (Fig. 16.7). Localized forms Table 16.1

MECHANISMS AND CAUSES OF BRONCHIECTASIS

• Bronchial obstruction Carcinoma Fibrous stricture (e.g. tuberculosis) Broncholithiasis Extensive compression (lymphadenopathy, neoplasm) • Parenchymal fibrosis (traction bronchiectasis) Tuberculosis Sarcoidosis Idiopathic pulmonary fibrosis • Bronchial wall injury Cystic fibrosis Childhood viral and bacterial infection Immunodeficiency disorders Dyskinetic cilia syndrome Allergic bronchopulmonary aspergillosis Lung and bone marrow transplantation Panbronchiolitis Systemic disorders (rheumatoid arthritis, Sjögren’s syndrome, inflammatory bowel disease, yellow nail syndrome)

Figure 16.5 Tracheobronchomalacia. Axial CT acquired during dynamic expiratory manœuvre. The collapse of the tracheal lumen is almost complete. The tracheal lumen is crescentic in shape because of the bowing of the posterior membranous trachea.

α1-Antitrypsin syndrome Congenital Williams Campbell syndrome

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cardinal sign of bronchiectasis) (Fig. 16.8), internal bronchial diameter greater than that of the adjacent pulmonary artery (signet ring sign) (Fig. 16.9), visualization of bronchi within 1 cm of the costal pleura or abutting the mediastinal pleura, and mucus-filled dilated bronchi (see Fig. 16.4A). In varicose bronchiectasis, the bronchial lumen assumes a beaded configuration (Fig. 16.8). Cystic bronchiectasis is seen as a string of cysts caused by sectioning irregular dilated bronchi along their

Figure 16.7 Cystic fibrosis. The PA radiograph shows slight overinflation and the presence of multiple thin-walled ring shadows in the right lung and the upper part of the left lung, reflecting cystic bronchiectasis. Some ring shadows contain air–fluid levels.

Figure 16.6 Bronchiectasis and obliterative bronchiolitis. (A) PA chest radiograph shows oligaemia in the lung bases with pulmonary blood flow redistribution in the upper parts of the lungs and slight overinflation of the lungs, more marked on the right side. (B) Targeted image of the right lung base in the same patient shows tramlines and ring opacities reflecting the presence of dilated and thick-walled bronchi.

are frequently accompanied by atelectasis which may be mild and detected only because of vascular crowding, fissure displacement, or obscuration of part of the diaphragm.

Computed tomography findings The major sign of bronchiectasis on thin-collimation CT (highresolution CT [HRCT]) is dilatation of the bronchi, with or without bronchial wall thickening. Bronchial dilatation on CT is often manifested by lack of tapering of bronchial lumina (the

Figure 16.8 Allergic bronchopulmonary aspergillosis. HRCT shows cylindrical and varicose bronchiectasis in the right upper lobe and the apicoposterior segment of the left upper lobe. Small centrilobular nodules representing infectious or inflammatory bronchiolitis are seen in the anterior segment of the right upper lobe. An area of parenchymal consolidation surrounded by a halo of ground-glass opacity is present within the superior segment of the left upper lobe (arrow). (Reprinted from “Imagerie Thoracique de l’ Adulte, 3rd. ed., 2006, Flammarion, with permission).

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Figure 16.9 Cystic fibrosis. HRCT image in the upper lobes shows bilateral bronchiectasis and thickening of the bronchial walls.

lengths, or a cluster of cysts, caused by multiple dilated bronchi lying adjacent to each other (Fig. 16.10). Clusters of cysts are most frequently seen in atelectatic lobes. Air–fluid levels, caused by retained secretions, may be present in the dependent portion of the dilated bronchi. Secretion accumulation within bronchiectatic airways is generally easily recognizable as lobulated gloved finger, V- or Y-shaped densities (Figs 16.11 and 16.12). When oriented perpendicular to the data acquisition plane the filled dilated bronchi are visualized as nodular opacities and recognized by observation of the homologous pulmonary arteries, whose diameters are smaller than those of the dilated filled bronchi. CT may show a completely collapsed lobe containing bronchiectatic airways. Subtle degrees of volume loss may be seen in lobes in relatively early disease.This is most evident in the lower lobes on the basis of crowding of the mildly dilated bronchi and posterior displacement of the oblique fissure. Associated CT findings of bronchiolitis are seen in about 70% of patients with bronchiectasis. Small centrilobular nodu-

Figure 16.10 Post-infectious cystic bronchiectasis. Presence of the clusters of cysts abutting the mediastinum and located within the left lower lobe and the inferior segment of the lingula. There is volume loss of the left lower lobe.

Figure 16.11 Allergic bronchopulmonary aspergillosis. HRCT of the upper lobes. Mucoid impactions are present within segmental and subsegmental dilated bronchi in the upper lobes. Small centrilobular linear branching opacities are seen in the periphery of the right upper lobe.

lar and linear branching opacities (tree-in-bud sign) express inflammatory and infectious bronchiolitis (Fig. 16.12). Areas of decreased attenuation and vascularity, mosaic perfusion pattern and expiratory air trapping reflect the extent of obliterative bronchiolitis (Fig. 16.13). These abnormalities are very common in patients with severe bronchiectasis and can even precede the development of bronchiectasis. The obstructive defect found at pulmonary tests in patients with bronchiectasis seems not to be related to the degree of collapse of large airways on expiratory CT or the extent of mucous plugging

Figure 16.12 Bronchiectasis with mucoid impactions and infectious bronchiolitis. Oblique reformat (4-mm thick slab) of the right lung with maximum intensity projection. Presence of mucoid impactions (arrows) in the dilated bronchi located within the anterior segment of the right upper lobe. Presence of multiple small centrilobular nodular and linear branching opacities (tree-in-bud sign).

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Cystic fibrosis1,4

Figure 16.13 Bronchiectasis and obliterative bronchiolitis. HRCT performed at full expiration shows air trapping in the right middle lobe, the superior segment of the left lower lobe, and some lobules of the left upper and right lower lobes. There is a cluster of cysts (cystic bronchiectasis) in the right middle lobe.

of the airway, but the consequence of an obstructive involvement of the peripheral airways (obliterative bronchiolitis)9. The extent of small airway disease commonly evident on CT (decreased lung attenuation, expiratory air trapping) in patients with bronchiectasis has proven to be the major determinant of airflow obstruction.

Accuracy of CT HRCT has replaced bronchography in the diagnosis and assessment of the extent of bronchiectasis10. By combining helical volumetric CT acquisition and thin collimation, CT has gained greater advantages by circumventing the limitations of HRCT, particularly the risk of missing bronchiectasis strictly localized within the intervals between slices11. Currently, MDCT with thin collimation is the technique of choice for the detection and the assessment of the extent of bronchiectasis. Multiplanar reformations increase the detection rate and the reader’s confidence as to the distribution of bronchiectasis, and improves agreement between observers as to the diagnosis12. In addition, maximum intensity projections improve the detection and display of both mucoid impactions and small centrilobular and linear branching opacities (tree-in-bud sign), characteristic of infectious bronchiolitis. The reliability of CT for determining the causes of bronchiectasis is somewhat controversial. An underlying cause for bronchiectasis is found in fewer than half of patients and CT features alone do not usually allow a confident distinction between idiopathic bronchiectasis and bronchiectasis with a specific cause4. Bilateral upper lobe distribution is most common in patients with cystic fibrosis and allergic bronchopulmonary aspergillosis; unilateral upper lobe distribution is most common in patients with tuberculosis; and a lower lobe distribution is most often seen after childhood viral infections. However, CT remains of little value in diagnosing specific aetiologies of bronchiectasis.

Cystic fibrosis results from an autosomal recessive genetic defect in the structure of the cystic fibrosis transmembrane regulation protein which leads to abnormal chloride transport across epithelial membranes. Although the mechanisms by which this defect leads to lung disease are not entirely understood, an abnormally low water content of airway mucus is at least partially responsible for decreased mucus clearance, mucous plugging of airways and an increased incidence of bacterial airway infection. Bronchial wall inflammation progressing to secondary bronchiectasis is always present in patients with long-standing disease. In patients with early or mild disease, the findings on chest radiography may be subtle. Hyperinflation reflects the presence of obstruction of the small airways (see Fig. 16.7). Thickening of the wall of the upper lobar bronchi can also be seen on the lateral radiograph. In more advanced disease, the radiographs can be diagnostic, showing increased lung volume, accentuated linear opacities in the upper lung areas, resulting from bronchial wall thickening or bronchiectasis, proximal bronchiectasis and mucoid impaction. Additional findings include cystic regions of the upper lobes (see Fig. 16.7), representing cystic bronchiectasis, healed abscess, cavities, or bullae; and atelectasis, findings of pulmonary hypertension or cor pulmonale, pneumothorax or pleural effusion. The chest radiographs are sufficient for clinical management, but it is important to know that usually there is a little visible radiographic change associated with clinical exacerbation. Several studies have shown that CT can offer an alternative to routine radiographic and clinical methods for monitoring disease status and progression as well as for assessing response to treatment. These studies consistently document close correlation between HRCT findings and both clinical and pulmonary functional evaluation of these patients. On CT, peripheral and/or central bronchiectasis is present in all patients with advanced cystic fibrosis (see Fig. 16.9). All lobes are typically involved, although early in the disease abnormalities are often predominantly distributed in the upper lobes, and sometimes with a right upper lobe predominance. Bronchial wall and/or peribronchial interstitial thickening is also commonly present. It is generally more evident than bronchial dilatation in patients with early disease. Mucous plugging is present in 25–50% of patients, and may be seen in all lobes. Collapse or consolidation is visible in up to 80% of patients. Lobar volume loss is often present in patients with advanced disease. Bullae may be difficult to distinguish from cystic bronchiectasis, particularly in fibrotic upper lobes. Abscesses may be difficult to distinguish from cystic bronchiectasis, particularly as both may contain air–fluid levels. Pleural thickening, which is often apparent on chest radiographs, is demonstrated to advantage by CT. Small centrilobular nodular and branching linear opacities (tree-in-bud sign) can be an early sign of disease.They reflect the presence of mucous impactions in dilated bronchioles associated with peribronchiolar inflammation. Focal areas of decreased lung attenuation are frequently present, representing air trapping and mosaic perfusion due to obstruction of the small airways. These areas often correspond to lobules and subsegments where mucous plugging in dilated airways is present.

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LARGE AIRWAY DISEASE AND CHRONIC AIRWAY OBSTRUCTION

At an early stage of the disease, HRCT can demonstrate airway abnormalities in patients who are asymptomatic and have normal pulmonary function and a normal chest radiograph. In patients with more advanced disease, HRCT is superior to chest radiography in detecting bronchiectasis and mucous plugging.

dilection. Despite this upper lobar shrinkage, the lung volume is frequently increased, reflecting overinflation in the lower lobes due to obstruction of the small airways and the presence of bullae in cavitation in the upper lobes.

Allergic bronchopulmonary aspergillosis1, 4

The dyskinetic cilia syndrome results from an autosomal recessive genetic abnormality and is characterized by abnormal ciliary structure and function, leading to a reduced mucociliary clearance and chronic airway infection. Bronchiectasis and sinusitis are common manifestations. About half of patients have also situs inversus. The combination of bronchiectasis, sinusitis and situs inversus is termed Kartagener’s syndrome. Men and women are equally affected, but in men the syndrome may be associated with immotile spermatozoa and infertility. Respiratory symptoms can generally be traced back to childhood. Bronchiectasis develops in childhood and adolescence and is associated with recurrent pneumonia. Both plain radiographs and CT typically show bilateral bronchiectasis with a basal (lower or middle lobe) predominance, similar to that seen in patients with other causes of postinfectious bronchiolitis. Cylindrical bronchiectasis is the most common type and a diffuse bronchiolitis may be present.

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity reaction to aspergillus and is characterized by asthma, blood, eosinophilia, radiographic pulmonary opacities and evidence of allergy to antigens of aspergillus species. It may also occur in patients with cystic fibrosis. Recurrent acute episodes cause progressive lung damage that can be controlled with steroids. The radiological features can be classified as acute and transient, or chronic and permanent. The most common acute changes are transient consolidation, mucoid impaction and atelectasis. Consolidation ranges from massive and homogeneous to lobar or segmental in configuration, or to subsegmental or smaller. When consolidation clears, it often leaves residual bronchiectasis, which creates a favourable environment for fungal recolonization, a finding that accounts for the fact consolidation often recurs in the same area. Mucoid impaction obstructs the airway lumen which becomes distended by retained secretions. At the same time, lung parenchyma remains aerated by collateral drift, permitting the visualization of the impacted airway. Bronchoceles appear as opacities of a variety of shapes (linear, branching or non-branching, band-like opacities that point to the hilum, toothpaste opacities, V- and Y-shaped opacities, gloved finger opacities). These opacities disappear once their airway contents have been coughed up, leaving ring or parallel linear opacities. Atelectasis is subsegmental, segmental or lobar and has a tendency to recur in the same area. Permanent changes indicate irreversible lung damage and are the clue that an asthmatic patient has ABPA when he/ she is in remission. Bronchiectasis is responsible for most of the permanent radiological changes. It affects lobar bronchi and the first- and second-order segmental bronchi. Beyond the proximal bronchi, more distal airways remain normal and patent, though small airway abnormalities are present on HRCT. These abnormalities include the tree-in-bud appearance reflecting mucoid impaction in dilated bronchioles, focal areas of decreased lung attenuation, and air trapping reflecting obstruction of the small airways. Compared with other bronchiectatic diseases, bronchiectasis in ABPA is more commonly widespread in central location, and more likely to contain cystic or varicose components. Mucus plugs within the ectatic airways are frequently seen on HRCT (see Fig. 16.11). High attenuation within the plugs is also relatively frequent, reflecting the presence of calcium concentration by the fungus. Hyperattenuated mucous plugs may be depicted within the areas of consolidation. Parenchymal scarring represents the fibrotic stage of the disease. It commonly follows bronchiectasis, and manifests as linear opacities and lobar shrinkage. Mirroring the distribution of bronchiectasis, these features have a strong upper zone pre-

Dyskinetic cilia syndrome1,4

BRONCHOLITHIASIS3,8 Broncholithiasis is a condition in which peribronchial calcified nodal disease erodes into or distorts an adjacent bronchus. The underlying abnormality is usually granulomatous lymphadenitis caused by Mycobacterium tuberculosis or fungi such as Histoplasma capsulatum. A few cases have been reported with silicosis. Calcified material in a bronchial lumen or bronchial distortion by peribronchial disease results in airway obstruction. This leads to collapse, obstructive pneumonitis, mucoid impaction, or bronchiectasis. Symptoms include cough, haemoptysis, recurrent episodes of fever and purulent sputum. Broncholithiasis is more common on the right, and obstructive changes particularly affect the right middle lobe. On chest radiographs, three major types of changes may be seen: • disappearance of a previously identified calcified nidus • change in position of a calcified nidus • evidence of airway obstruction, including segmental or lobar atelectasis, mucoid impaction, obstructive pneumonitis, obstructive oligaemia with air trapping. Calcified hilar or mediastinal nodes are a key feature. CT and fibre-optic bronchoscopy complement each other in this condition. Broncholithiasis is recognized on CT by the presence of a calcified endobronchial or peribronchial lymph node, associated with a bronchopulmonary complication caused by obstruction (including atelectasis, pneumonia, bronchiectasis and air trapping), in the absence of an associated soft tissue mass.

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EMPHYSEMA1,3,6,13 Emphysema is defined as a condition of the lung characterized by permanent, abnormal enlargement of airspaces distal to the terminal bronchioles, accompanied by the destruction of their walls without obvious fibrosis. The most important aetiological factor by far is cigarette smoking. Other inhaled pollutants have also been implicated, including gases such as nitrogen oxides and phosphogenes, as well as particulate smoke. There is also a causal relationship between HIV infection and the development of early emphysema. Various genetic disorders associated with emphysema include α1-antitrypsin deficiency, heritable diseases of connective tissue such as cutix laxa, Marfan syndrome and familial emphysema. Emphysema is thought to result from the destruction of elastic fibres caused by an imbalance between proteases and protease inhibitors in the lung and from the mechanical stresses of ventilation and coughing. Proteases are normally released in low concentration by phagocytes in the lung. Protease inhibitors, mainly α1-protease inhibitor (α1-antitrypsin), prevent them from causing structural damage to the lung. Imbalance in the protease–antiprotease activity may result from antiprotease deficiency (α1-antitrypsin deficiency) from excess release of protease stimulated by environmental agents, or from the defective repair of protease-induced damage. Tobacco smoke increases the number of pulmonary macrophages and neutrophils, reduces antiprotease activity, and may impair the synthesis of elastin. As emphysema develops lung destruction progresses, airspaces enlarge and elastic recoil declines, reducing radial traction on bronchial walls and on blood vessels, allowing airways and vessels to collapse.

Pathological classification Classification of emphysema is traditionally based on the microscopic localization of disease within the secondary pulmonary lobule. The principal types are centrilobular, panlobular, paraseptal and irregular emphysema. Centrilobular (centriacinar) emphysema affects mainly the proximal respiratory bronchioles and alveoli in the central part of the acinus. The process tends to be most developed in upper parts of the lungs. It is strongly associated with cigarette smoking. Inflammatory changes in the small airways are common with plugging, mural infiltration and fibrosis, leading to stenosis, distortion and destruction. Paraseptal emphysema selectively involves the alveoli adjacent to the connective tissues of septa and bronchovascular bundles, particularly at the margins of the acinus and lobule but also subpleurally and adjacent to the bronchovascular bundles. Airspaces in paraseptal emphysema may become confluent and develop into bullae, which may be large. Airway obstruction and physiological disturbance may be minor. Panlobular (panacinar) emphysema is characterized by a dilatation of the airspaces of the entire acinus and lobule. With progressive destruction, all that eventually remains are thin strands of deranged tissue surrounding blood vessels. It is the most widespread and severe type of emphysema. Pathological changes are distributed throughout the lungs, but they

are often basely predominant. Panlobular emphysema is the type of emphysema that occurs in α1-antitrypsin deficiency and in familial cases. Irregular (or paracicatricial) emphysema refers to irregular airspace enlargement, and occurs in patients with pulmonary fibrosis. It is commonly seen adjacent to localized parenchymal scars, in diffuse pulmonary fibrosis, and in pneumoconiosis, particularly progressive massive fibrosis.

Radiographic findings The main radiographic manifestations of emphysema are overinflation and alterations in the lung vessels. Signs of overinflation are the best predictors of the presence and severity of emphysema. Signs of overinflation include the height of the right lung being greater than 29.9 cm, location of the right hemidiaphragm at or below the anterior aspect of the seventh rib, flattening of the hemidiaphragm, enlargement of the retrosternal space, widening of the sternodiaphragmatic angle and narrowing of the transverse cardiac diameter (Fig. 16.14). Alterations in lung vessels include arterial depletion, whereas vessels of normal, or occasionally increased, calibre are present in unaffected areas of the lung, absence or displacement of vessels caused by bullae, widened branching angles with loss of side branches and vascular redistribution. With the development of cor pulmonale, or left heart failure, the radiographic appearance will alter and may become less obviously abnormal. The heart may then appear to be normal in size, or sometimes enlarged, the diaphragm becomes less flat and the pulmonary vessels less attenuated. Bullae may be as small 1 cm in diameter or may occupy the whole hemithorax causing marked relaxation collapse of the adjacent lung. Bullae caused by paraseptal emphysema are much more common in the upper zones, but when they are associated with widespread panlobular emphysema, the distribution is much more even. Occasionally the wall is completely absent and in such cases bullae can be difficult to detect. Plain radiographs markedly underestimate the number of bullae. The presence of emphysema associated with large bullae is referred to as bullous emphysema. An entity mainly seen in young men, characterized by the presence of large progressive upper lobe bullae which occupy a significant volume of a hemithorax and are often asymmetrical, is referred to as giant bullous emphysema, vanishing lung syndrome or primary bullous disease of the lung. Large bullae may be seen as avascular transradiant areas usually separated from the remaining lung parenchyma by a thin curvilinear wall (Fig. 16.15). They can cause marked relaxation collapse of the adjacent lung and can even extend into the opposite hemithorax, particularly by way of the anterior junctional area. Spontaneous pneumothorax commonly occurs in association with localized areas of emphysema or bullae affecting the lung apices. Bullae may enlarge progressively over months or years; a period of stability may be followed by a sudden expansion. Bullae may also disappear, either spontaneously or following infection or haemorrhage. The main complications of bullae include pneumothorax, infection and haemorrhage. In case of

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Figure 16.15 Giant bullous emphysema. The PA chest radiograph shows large avascular transradiant areas in the upper and lower parts of the right lung. The bullae are marginated with thin curvilinear opacities.

Computed tomography findings CT, particularly HRCT, is the most accurate means of detecting emphysema and determining its type and extent in vivo. On HRCT, emphysema is characterized by the presence of areas of abnormally low attenuation which can be easily contrasted with surrounding normal lung parenchyma if sufficiently low window values (−800 to −1000 HU) are used. Focal areas of emphysema usually lack distinct walls as opposed to lung cysts. In many patients, it is possible to classify the type of emphysema on the basis of its HRCT appearance, although the different types, as well as bullae, may be present in association in the same patient.

Centrilobular emphysema Figure 16.14 Severe diffuse emphysema. (A) PA and (B) lateral chest radiographs. The diaphragm is displaced downwards and appears flattened. On the PA radiograph (A) the transverse cardiac diameter is reduced. The diaphragm appears irregular in contour due to an abnormal visibility of diaphragmatic insertions on the ribs. Note the depression of vessels in the periphery of the lungs. On the lateral radiograph (B) there is a widening of the sternodiaphragm angle and an increase of dimensions of the retrosternal transradiant area.

infection or haemorrhage, bullae contain fluid and develop an air–fluid level.When a bulla becomes infected the hairline wall becomes thickened and may mimic a lung abscess. Carcinoma arising in or adjacent to bullae should be suspected in case of mural nodule, mural thickening, a change in diameter of the bulla, pneumothorax and the accumulation of fluid within the bulla.

Centrilobular emphysema predominantly affects the central portion of the lobule. On HRCT it is characterized by the presence of multiple, small round areas of abnormally low attenuation, distributed throughout the lungs but commonly having an upper lobe predominance (Fig. 16.16)14.The emphysematous spaces often appear to be grouped near the centre of secondary lobules surrounding the centrilobular arteries. Even when the centrilobular location of low attenuation areas is not recognized on HRCT, the presence of multiple, small areas of emphysema scattered throughout the lung is diagnostic of centrilobular emphysema. As the emphysema becomes more severe the areas of low attenuation become confluent and the centrilobular distribution becomes less apparent. In most cases, the areas of low attenuation have no visible walls. However, sometimes very thin walls may be seen when the areas of emphysema are extensive. These apparent walls probably represent atelectasis or interlobular septa adjacent to the emphysematous spaces.

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Occasionally the remaining interlobular septa may appear particularly prominent on the chest radiograph and in this way mimic lymphangitic carcinomatosis. HRCT of course will readily identify the true cause.

Panlobular emphysema Panlobular emphysema is characterized by widespread areas

of abnormally low attenuation, representing the uniform destruction of the pulmonary lobule. Pulmonary vessels in the affected lung appear fewer and smaller than normal (Fig. 16.18). Panlobular emphysema is almost always most severe in the lower lobes, where long lines may be present reflecting the presence of fibrosis within the remaining interlobular septa (Fig. 16.18). The characteristic appearances of extensive lung destruction and the associated paucity of vascular markings are easily recognized. On the other hand, mild and even moderately severe panlobular emphysema can be very subtle and difficult to detect radiologically15. Panlobular emphysema, secondary to α1-antitrypsin deficiency, is frequently associated with bronchiectasis. Figure 16.16 Centrilobular emphysema. HRCT of the right lung shows multiple small round areas of low attenuation that are distributed through the lungs, mainly around the centrilobular arteries (arrows).

Irregular emphysema

Paraseptal emphysema

mally low attenuation associated with features of fibrosis. It may be associated with diffuse pulmonary fibrosis or progressive massive fibrosis.

Paraseptal emphysema is characterized on HRCT by areas of low attenuation visible in the subpleural areas, along the peripheral or mediastinal pleura, mainly in the upper lobe and along the fissures (Fig. 16.17). The emphysematous spaces often have very thin but visible walls, mostly corresponding to interlobular septa thickened by associated fibrosis. Subpleural bullae are a frequently associated finding. They are commonly found in the azygoesophageal recess, adjacent to the superior mediastinal border and along the anterior junctional region. Because of its location adjacent to structures with soft-tissue attenuation, even mild paraseptal emphysema is easily detected on HRCT.

Figure 16.17 Paraseptal emphysema. HRCT of the right upper lobe shows multiple small areas of low attenuation distributed along the peripheral and mediastinal pleura (arrows).

Irregular emphysema is recognized on HRCT as areas of abnor-

Bullae Bullae are seen as avascular, low-attenuation areas that are larger than 1 cm in diameter and that can have a thin but perceptible wall. In most patients the parenchymal abnormalities are not visible on the chest radiograph. CT is more sensitive than the chest radiograph in demonstrating bullae and allows accurate assessment of their number, size, and position. CT is particularly useful when there is difficulty in distinguishing bullous disease from pneumothorax (Fig. 16.19A)16. Inspiratory and expiratory CT images indicate the extent to which a bulla is ventilated and the appearance of the rest of the lung helps in assessing the extent and degree of diffuse lung disease. This

Figure 16.18 Panlobular emphysema in a patient with α1-antitrypsin deficiency. HRCT of the lung bases showing the presence of large areas of decreased lung attenuation with a paucity of pulmonary vessels, more marked in the lower lobes. Long lines are visible within the remaining parenchyma of lung bases.

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can be highlighted on a CT image (density mask technique) and expressed as a percentage of the total pixels included in the lung section (Fig. 16.19B)18. Gevenois et al have shown that a threshold of −950 HU provides an accurate estimate of both macroscopic and, to a slightly lesser degree, microscopic emphysema19,20. However, this technique is very sensitive to technical factors. In particular, reducing the milliamperage may affect the measured extent of low attenuated lung. With MDCT, it has become feasible to apply density thresholding technique to volumetric data. Lung volume and volume of emphysema are quantified and displayed at a regional level, for a better preoperative assessment of lung disease in patients with severe emphysema who are candidates for bullectomy, lung volume reduction surgery, or lung transplantation. The use of the density mask method on both expiratory and inspiratory images has been used as a means of distinguishing areas of simple hyperinflation without tissue destruction from areas of emphysema. Expiratory CT does not correlate as well as inspiratory HRCT with the morphological extent of emphysema, but the expiratory HRCT is superior to inspiratory HRCT in reflecting functional air trapping. This technique has shown good correlations with indices of airflow obstruction and air trapping, particularly when a threshold of −900 HU is used.

CHRONIC BRONCHITIS1,6,13

Figure 16.19 Giant bullous emphysema. (A) Coronal reformation after MDCT thin collimation acquisition. Presence of large confluent bullae within the right lung associated with destruction of the right upper lobe. Presence of paraseptal emphysematous bullae within the left upper lobe along the mediastinum. (B) The same coronal reformation as in (A) after applying the density mask technique (−950 HU), making it possible to segment automatically the areas of emphysema before quantitative assessment.

ability makes CT useful for identifying patients suitable for treatment with bullectomy.

Assessment of extent of emphysema with computed tomography The distribution and severity of emphysema may be quantitated by CT. CT can be assessed by subjective visual methods, density measurements or by post-processing and texture analysis. Studies using various CT section thicknesses have shown good correlation between macroscopic pathological scores and visually assessed CT scores. However, intraand inter-observer variation in such subjective approaches is low to moderate. Objective methods using CT densitometry provides better correlation with a morphological reference17. The density of emphysematous areas is abnormally low. If a histogram plot is made of frequency against pixel density (HU), the emphysematous curve is shifted to the left compared with normal. Pixels with values below a certain number

Chronic bronchitis is defined as a clinical disorder characterized by excessive mucus secretion by the bronchial tree, manifested by chronic or recurring productive cough on most days in more than 3 months of each of 2 successive years. The pathogenesis of chronic bronchitis is related to cigarette smoking, air pollution and infection. The histological abnormalities present in chronic bronchitis include bronchial submucosal hyperplasia, smooth muscle hypertrophy, chronic inflammation and the obstruction of small airways. On pulmonary function tests, a patient with pure chronic bronchitis has normal total lung capacity and normal elastic recoil, but reduced expiratory flow and elevated residual volume. Airflow obstruction, which is concentrated in the small bronchioles, has both reversible (mucous plugging, inflammation, smooth muscle hypertrophy) and irreversible components (fibrosis and stenosis).

Radiographic findings The majority of patients with symptoms of chronic bronchitis have a normal chest radiograph. When radiographic abnormalities are present, they can include hyperinflation, oligaemia, bronchial wall thickening and accentuation of linear lung markings. Hyperinflation and oligaemia (sparse and attenuated lung vessels) can occur in patients with chronic bronchitis in the absence of emphysema, as a result of obstruction of the small airways (Fig. 16.20). Thickening of the bronchial walls leads to tubular and ring shadows. Increased lung markings cause the appearance of a ‘dirty chest’, a term widely used for describing a loss in clarity of the lung vessels (Fig. 16.20). In spite of these findings, it is

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Figure 16.20 Chronic bronchitis and obstructive lung disease. PA chest radiograph shows mild overinflation. A ring shadow is visible above the left hilum (arrow) reflecting bronchial wall thickening. There is also accentuation of linear markings in the right lung base.

widely admitted that the chest radiograph has little to offer in the detection or exclusion of chronic bronchitis. Sabre-sheath trachea may be present. Cor pulmonale is a recognized complication which is seen almost exclusively in hypoxic patients. With the onset of heart failure the heart and hilar and intermediate lung vessels become enlarged. Enlargement of vessels is present in all zones and affects particularly segmental vessels and a few divisions beyond.

Computed tomography findings On CT, bronchial wall thickening is present. Using thin-collimation MDCT acquisition and multiplanar reformations associated with minimum intensity projections, air-filled outpouchings or diverticula are seen in addition to the lumen of the main lobar or segmental bronchi. These abnormalities reflect the enlargement of mucous glands and are related to low or subepithelial connective tissue and herniation of airway mucosa between small muscle bundles. Because of the deficit of bronchial cartilage in patients with COPD, prominent collapse of airway lumen may occur with maximum force expiratory manœuvre. On expiratory CT, the lumen of segmental and subsegmental bronchi (mainly in the lower lobes) may collapse excessively, particularly in the lower lobes where the cartilage deficiency is most apparent. Airway remodelling occurs in COPD patients, but this abnormality involves essentially the small airways. As there is a significant association between the dimension of the small and large airways in COPD patients, measuring airway dimension in the larger bronchi can provide an estimate of small airway remodelling. It is likely that the same pathophysiological process that causes small airway obstruction also

takes place in larger airways where its functional effects are smaller. By using CT to assess the extent of emphysema and measure airway wall area in a cohort of COPD patients and asymptomatic smokers, some investigators have shown that individual COPD patients may have emphysema or airway wall remodelling as their predominant phenotypes21.The ability to separate airway-predominant from parenchymal-predominant pathology in COPD may prove useful in applying specific therapies designed to prevent or ameliorate the airway remodelling or parenchymal destruction. In the lung parenchyma, thin-section CT has proven its ability in demonstrating the presence of small airway abnormalities and centrilobular emphysema in asymptomatic smokers, before the development of an obstructive lung disease (Fig. 16.21). In a study of healthy adult volunteers, 20–25% of the smokers showed multiple areas of ground-glass attenuation and small nodules (Fig. 16.21)22. In another CT–pathology correlation study in heavy smokers, the areas of ground-glass attenuation corresponded to histological findings of respiratory bronchiolitis and the small centrilobular nodules corresponded to bronchiolectasis with peribronchiolar fibrosis23. The introduction of expiratory thin-section CT has demonstrated that air trapping observed in healthy volunteers is related to smoking and can be observed before pulmonary function deteriorates. In patients with COPD, the extent of lung hypoattenuation at expiration probably reflects air trapping more than reduction of the alveolar wall surface. However, expiratory air trapping in these patients may be the result of either airway obstruction caused by a loss of alveolar attachment to the airways, directly related to emphysema, or of intrinsic bronchial or bronchial abnormalities associated with cigarette smoking.

ASTHMA1,8 Asthma is a chronic inflammatory condition involving the airways. This inflammation causes a generalized increase in existing bronchial hypersensitivity to a variety of stimuli. This is commonly used in practice to confirm the clinical diagnosis of asthma. In susceptible individuals, this inflammation induces recurrent episodes of wheezing, chest tightness, breathlessness

Figure 16.21 Respiratory bronchiolitis and centrilobular emphysema in a heavy smoker. HRCT of the upper lobes shows patches of groundglass opacity associated with areas of centrilobular emphysema.

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and coughing, usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment. The chronic inflammation process leads to structure changes, such as new vessel formation, airway smooth muscle thickening and fibrosis, which may result in irreversible airway narrowing.

Radiographic findings Chest radiography is usually recommended in all asthmatic patients who are ill enough to justify admission to a hospital. Hyperinflation may be seen in both relapse and remission.The prevalence of hyperinflation is generally higher in children and in patients needing hospital admission. While hyperinflation is often transient, it may be a permanent change. Bronchial wall thickening is more frequent in children, but in adults when it becomes visible it is usually an irreversible phenomenon. The walls of end-on segmental airways become thickened and the normally invasive airways parallel to the radiographs appear as parallel or single line opacities. It may be present in up twothirds of patients. Chest radiography may depict complications including consolidation, atelectasis, mucoid impaction, pneumothorax and pneumomediastinum. Consolidation is commonly infective but in some cases it is due to eosinophilic consolidation probably associated with allergic aspergillosis. Collapse ranges from subsegmental to lobar and occasionally involves the whole lung. Collapse is due to mucoid impaction in large airways or more commonly mucous plugging in many small airways.

Computed tomography findings The clinical indications for CT in patients with asthma include the detection of bronchiectasis in patients with suspected ABPA, the documentation of the presence and extent of emphysema in smokers with asthma, and the identification of conditions that may be confused with asthma, such as hypersensitivity pneumonitis. In uncomplicated asthma, HRCT may show bronchial dilatation, bronchial wall thickening, mucoid impaction, decreased lung attenuation, air trapping and small centrilobular opacities24,25. These abnormalities may or may not be reversible with steroid treatment. The prevalence of these thin-section CT abnormalities increases with increasing severity of symptoms. Considerable variation exists, however, in the reported frequency of abnormalities. This variation is related to differences in diagnostic criteria and patient selection. Bronchial wall thickness measured on CT is prominent in patients with more severe asthma26. It correlates with the duration and severity of disease and the degree of airflow obstruction. Peribronchial inflammation may be partly responsible for the bronchial wall thickening, but if this feature is not reversible with steroid treatment, it reflects the development of hyperplasia and hypertrophy of smooth muscle on the bronchial wall reflecting airway wall remodelling. This observation supports the concept that quantitative assessment of bronchial wall area on CT could be used to assess airway wall remodelling in asthmatic patients in longitudinal studies to evaluate the effects of new therapies.



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Focal and diffuse areas of decreased lung attenuation seen in 20–30% of asthmatic patients are likely the results of a combination of air trapping and pulmonary oligaemia owing to alveolar hypoventilation. The areas of decreased attenuation in acute asthma almost always reflect hypoxic vasoconstriction in parts of the lung that are underventilated as a result of bronchospasm, and such areas of air trapping are more conspicuous and extensive on expiratory CT. In chronic asthma, morphological features of emphysema on CT are almost invariably related to cigarette smoking, rather than the asthma per se, in which the decreased attenuation areas represent small airway obstruction. Expiratory CT can show abnormal air trapping even in patients who have normal inspiratory images. The extent of such air trapping correlates with the severity of the asthma. Abnormal expiratory air trapping has been observed in 50% of asthmatic patients.This reflects the luminal obstruction of the airways and is potentially, but not always, reversible. CT may depict air trapping before lung function deteriorates. The mosaic perfusion pattern is frequent in patients with moderate persistent asthma27. In severe persistent asthma, diffuse decreased lung attenuation and expiratory air trapping make the pattern difficult to distinguish from that of obliterative bronchiolitis. In patients with persistent asthma, no change in air trapping scores after inhalation of a bronchodilator suggest that the air trapping may reflect permanent changes resulting from small airway remodelling27. Airway remodelling caused by smooth muscle hypertrophy and hyperplasia accounts for the faster and greater decrease in forced expiratory volume per second with age in asthmatics compared with controls.

OBLITERATIVE (CONSTRICTIVE) BRONCHIOLITIS1,3,4,6,13 Inflammation of the bronchioles (bronchiolitis) is a very common lesion in the lungs. However, the extent of such lesions is rarely extensive enough to cause clinical symptoms. Pathological studies have repeatedly emphasized the frequent involvement of the bronchioles in diverse diffuse disease. Inflammation of the bronchioles may be reversible under specific or antiinflammatory treatment or lead to subsequent scaring and obliteration. Obliterative bronchiolitis is a condition characterized by bronchiolar and peribronchiolar inflammation and fibrosis that ultimately leads to luminal obliteration affecting the membranous and respiratory bronchioles. Obliterative bronchiolitis is the result of a variety of causes but in rare cases it is idiopathic (Table 16.2). When a large proportion of the airways is affected, patients usually present with progressive shortness of breath and functional evidence of airflow obstruction.

Pathological features The pattern of obliterative bronchiolitis is characterized by the development of an irreversible circumferential submucosal fibrosis, resulting in bronchiolar narrowing or obliteration of bronchioles in the absence of intraluminal granulation tissue polyps or surrounding parenchymal inflammation. Proliferation of fibrosis extends predominantly between the epithelium

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Table 16.2 CAUSES OF AND ASSOCIATION WITH OBLITERATIVE (CONSTRICTIVE) BRONCHIOLITIS • Postinfection Childhood viral infection (adenovirus, respiratory syncytial virus, influenza, parainfluenza) Adulthood and childhood (Mycoplasma pneumoniae, Pneumocystis carinii in AIDS patients, endobronchial spread of tuberculosis, bacterial bronchiolar infection) • Postinhalation (toxic fume and gases) Nitrogen dioxide (silo filler’s disease), sulphur dioxide, ammonia, chlorine, phosgene Hot gases • Gastric aspiration Diffuse aspiration bronchiolitis (chronic occult aspiration in the elderly, patients with dysphagia) • Connective tissue disorders Rheumatoid arthritis Sjögren’s syndrome • Allograft recipients Bone marrow transplant Heart–lung or lung transplant • Drugs Penicillamine Lomustine • Ulcerative colitis • Other conditions Bronchiectasis Chronic bronchitis Cystic fibrosis Hypersensitivity pneumonitis Sarcoidosis Microcarcinoid tumorlets (neuroendocrine cell hyperplasia) Sauropus androgynus ingestion • Idiopathic

and the muscular mucosa and along the long axis of the airway, impairing collateral ventilation and leading to airflow obstruction. The epithelium overlying the abnormal fibrosis tissue may be flattened or metaplastic and is usually intact without any ulceration. In some instances, the accompanying artery is also obliterated by the same fibrotic process.

Radiographic findings The chest radiograph is often normal. In a small number of patients, mild hyperinflation, subtle peripheral attenuation of the vascular markings, widespread and conspicuous abnormalities in lung attenuation, and central bronchiectasis may be seen (see Fig. 16.6). Thin-section CT is superior to radiography in demonstrating the presence and extent of abnormalities. The main thin-section CT findings usually consist of areas of decreased lung attenuation associated with vessels of decreased calibre on inspiratory images and air trapping on expiratory images. Because the lesions of bronchiolar narrowing or obstruc-

tion are heterogeneously distributed throughout the lungs, redistribution of blood flow to areas of normal lung or less diseased areas give a pattern of mosaic perfusion. Bronchial wall thickening and bronchiectasis, both central and peripheral, are also commonly present. Although the vessels within areas of decreased attenuation on thin-section CT may be of markedly reduced calibre, they are not distorted as in emphysema. The lung areas of decreased attenuation related to decreased perfusion can be patchy or widespread. They are poorly defined or sharply demarcated, giving a geographical outline, and represent a collection of affected secondary pulmonary lobules. Redistribution of blood flow to the normally ventilated areas causes increased attenuation of lung parenchyma in these areas. The patchwork of abnormal areas of low attenuation and normal lung or less diseased areas, appearing normal in attenuation or hyperattenuated, gives the appearance of mosaic attenuation. The vessels in the abnormal hypoattenuated areas are reduced in calibre, whereas the vessels in normal areas are increased in size; the resulting pattern is called mosaic perfusion. The difference in vessel size between low and high attenuation areas allows the mosaic perfusion pattern to be distinguished from mosaic attenuation due to an infiltrative lung disease with patchy distribution, in which the vessels have the same calibre in both high and normal attenuation areas.The areas of decreased lung attenuation and perfusion may be confined to or predominant in one lung, particularly in Swyer–James or MacLeod syndrome, which is a variant form of postinfectious obliterative bronchiolitis in which the obliterative bronchiolar lesions affect predominantly one lung. Usually the regional inhomogeneity of the lung density seen at end-inspiration on thin-section CT is accentuated on sections obtained at end, or during, expiration because the high attenuation areas increase in density and the low attenuation areas remain unchanged. In the case of more global involvement of the small airways, the lack of regional homogeneity of the lung attenuation is difficult to perceive on inspiratory CT, and as a result mosaic perfusion becomes visible only on expiratory images (Fig. 16.22). In patients with particularly severe and widespread involvement of the small airways, the patchy distribution of hypoattenuation and mosaic pattern is lost. On inspiratory CT there is uniformly decreased attenuation in the lungs, and images taken at end-expiration may appear unremarkable. In these patients, the most striking features are a paucity of pulmonary vessels and no difference in the cross-sectional areas of the lung at comparable levels on inspiratory and expiratory images. In such a situation, there is a risk of misdiagnosis between obliterative bronchiolitis and panlobular emphysema. Both conditions are characterized by bronchial wall thickening and generalized decreased attenuation of the lung parenchyma and bronchial dilatation. However, patients with panlobular emphysema demonstrate parenchymal destruction with higher frequency and greater extent than those with obliterative bronchiolitis. Long lines reflecting limited thickened interlobular septa were significantly more frequent in patients with panlobular emphysema28.

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Figure 16.22 Obliterative bronchiolitis. HRCT acquired at (A) full inspiration and (B) full expiration. The mosaic perfusion appearance is very difficult to perceive on the inspiration image (A). The contrast in attenuation between normal and abnormal areas is accentuated at expiration. The areas that did not change in attenuation between inspiration and expiration represent areas of lung parenchyma containing obliterative lesions on the bronchioles.

Assessment of air trapping with computed tomography The most commonly used CT technique for the assessment of air trapping is based on postexpiratory thin-section images obtained during suspended respiration following a forced exhalation. Each of the postexpiratory images is compared with the inspiratory image that most closely duplicates its level to detect air trapping. More recently, dynamic expiratory manœuvre performed during helical CT acquisition has been described29. Motion artefacts, which increase as temporal resolution decreases, represent the major limitation of continuous expiratory CT. However, motion artefacts are at a maximum during the early phase of expiration and at a minimum during its late phase, which allows good visualization of lobular air trapping with helical CT. The extent of air trapping and the relative contrast scores are significantly higher with continuous expiratory CT than those obtained with suspended end-



LARGE AIRWAY DISEASE AND CHRONIC AIRWAY OBSTRUCTION

expiratory CT. This improvement can be explained by a small increase in the degree of expiration, which leads to a better detection of air trapping29. This technique is recommended when patients have difficulty performing the suspended endexpiration manœuvre adequately. MDCT with thin collimation over the lungs and low dose has become routine in many institutions to improve the conspicuity and apparent extent of air trapping. The technique of multiplanar volume rendering slab associated with the technique of minimum intensity projection increases the contrast between areas of normal lung attenuation and areas of lung hypoattenuation. This helps depict the mosaic perfusion pattern. Its application in expiratory CT can also facilitate the detection of air trapping and the assessment of its extent. The texture analysis technique has been developed to discriminate between patterns of obstructive lung disease on the basis of parenchymal texture alone on HRCT. The extent of air trapping present on expiratory CT can be measured using a semiquantitative scoring system that estimates the percentage of lung that appears abnormal in each study. In the scoring system proposed by Stern et al, estimates of air trapping were made at each level and for each lung on a four-point scale: 0: no air trapping; 1: 1–25%; 2: 26–50%; 3: 51–75%; and 4: 76–100% of the cross-sectional area of the lung affected. The air trapping score is the summation of these numbers for the level studied.This scoring system allows good inter- and intra-observer agreement. The extent of expiratory air trapping at CT has proved to correlate with the degree of airflow obstruction at pulmonary function tests in patients with obliterative bronchiolitis30. Objective measurement of air trapping can be done using CT densitometry. The assessment of extent can be expressed as a mean density of the voxels included in a chosen region of interest; as a histogram that shows the distribution of attenuation values within the lung; and as a density mask that highlights, or as a calculation that summarizes, the pixels with a density below a certain critical value. In the density mask technique, all the pixels included in areas of air trapping are segmented by thresholding at −910 HU and are highlighted and automatically counted. This permits calculation of the pixel index, which is defined as the percentage of pixels in both lungs on a single study that show an attenuation lower than a predetermined threshold value. Expressing lung density on a histogram has the advantage that changes in the distribution of attenuation values are detectable when mean attenuation is unchanged. Density changes between full inspiration and full expiration can be compared, and expiratory:inspiratory ratios can be calculated. The density mask has the advantage that it combines density measurement with the visual assessment of pathology. Using MDCT with thin collimation over the lungs performed at full expiration, an exhaustive assessment of the volume of air trapping may be provided, as well as a 3D visualization of the distribution of air trapping. Sophisticated image processing techniques can be used to compensate for the nondependent–dependent lung attenuation gradient.

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REFERENCES 1. Hansell D M, Armstrong P, Lynch D A et al 2005 Imaging of diseases of the chest, 4th edn. Elsevier Mosby, Philadelphia 2. Kwong J S, Muller N L, Miller R R 1992 Diseases of the trachea and main-stem bronchi: correlation of CT with pathologic findings. RadioGraphics 12: 645–657 3. Muller N L, Fraser R G, Lee K S et al 2003 Diseases of the lung. Lippincott Williams & Wilkins, Philadelphia 4. Naidich D P, Webb W R, Grenier P A et al 2005 Imaging of the airways. Lippincott Williams & Wilkins, Philadelphia 5. Berkmen Y M 1984 The trachea: the blind spot in the chest. Radiol Clin North Am 22, 539–562 6. Takasugi J E, Godwin J D 1998 Radiology of chronic obstructive pulmonary disease. Radiol Clin North Am 36: 29–55 7. Baroni R H, Feller-Kopman D, Nishino M et al 2005 Tracheobronchomalacia: comparison between end-expiratory and dynamic expiratory CT for evaluation of central airway collapse. Radiology 235: 635–641 8. Grenier P A, Beigelman-Aubry C, Fetita C et al 2002 New frontiers in CT imaging of airway disease. Eur Radiol 12: 1022–1044 9. Roberts H R, Wells A U, Milne D G et al 2000 Airflow obstruction in bronchiectasis: correlation between computed tomography features and pulmonary function tests. Thorax 55: 198–204 10. Grenier P, Maurice F, Musset D et al 1986 Bronchiectasis: assessment by thin-section CT. Radiology 161: 95–99 11. Lucidarme O, Grenier P, Coche E et al 1996 Bronchiectasis: comparative assessment with thin-section CT and helical CT. Radiology 200: 673–679 12. Remy-Jardin M, Amara A, Campistron P et al 2003 Diagnosis of bronchiectasis with multislice spiral CT: accuracy of 3-mm-thick structured sections. Eur Radiol 13: 1165–1171 13. Webb W R 1994 High-resolution computed tomography of obstructive lung disease. Radiol Clin North Am 32: 745–757 14. Foster W L Jr, Pratt P C, Roggli V L et al 1986 Centrilobular emphysema: CT–pathologic correlation. Radiology 159: 27–32 15. Spouge D, Mayo J R, Cardoso W et al 1993 Panacinar emphysema: CT and pathologic findings. J Comput Assist Tomogr 17: 710–713 16. Stern E J, Webb W R, Weinacker A et al 1994 Idiopathic giant bullous emphysema (vanishing lung syndrome): imaging findings in nine patients. Am J Roentgenol 162: 279-282 17. Bankier A A, De Maertelaer V, Keyzer C et al 1999 Pulmonary emphysema: subjective visual grading versus objective quantification with macroscopic morphometry and thin-section CT densitometry. Radiology 211: 851–858

18. Muller N L, Staples C A, Miller R R et al 1988 “Density mask.” An objective method to quantitate emphysema using computed tomography. Chest 94: 782–787 19. Gevenois P A, de Maertelaer V, De Vuyst P et al 1995 Comparison of computed density and macroscopic morphometry in pulmonary emphysema. Am J Respir Crit Care Med 152: 653–657 20. Gevenois P A, De Vuyst P, de Maertelaer V et al 1996 Comparison of computed density and microscopic morphometry in pulmonary emphysema. Am J Respir Crit Care Med 154: 187–192 21. Nakano Y, Muro S, Sakai H et al 2000 Computed tomographic measurements of airway dimensions and emphysema in smokers. Correlation with lung function. Am J Respir Crit Care Med 162: 1102–1108 22. Remy-Jardin M, Remy J, Boulenguez C et al 1993 Morphologic effects of cigarette smoking on airways and pulmonary parenchyma in healthy adult volunteers: CT evaluation and correlation with pulmonary function tests. Radiology 186: 107–115 23. Remy-Jardin M, Remy J, Gosselin B et al 1993 Lung parenchymal changes secondary to cigarette smoking: pathologic–CT correlations. Radiology 186: 643–651 24. Grenier P, Mourey-Gerosa I, Benali K et al 1996 Abnormalities of the airways and lung parenchyma in asthmatics: CT observations in 50 patients and inter- and intraobserver variability. Eur Radiol 6: 199–206 25. Park C S, Muller N L, Worthy S A et al 1997 Airway obstruction in asthmatic and healthy individuals: inspiratory and expiratory thinsection CT findings. Radiology 203: 361–367 26. Niimi A, Matsumoto H, Amitani R et al 2000 Airway wall thickness in asthma assessed by computed tomography. Relation to clinical indices. Am J Respir Crit Care Med 162: 1518–1523 27. Laurent F, Latrabe V, Raherison C et al 2000 Functional significance of air trapping detected in moderate asthma. Eur Radiol 10: 1404–1410 28. Copley S J, Wells A U, Muller N L et al 2002 Thin-section CT in obstructive pulmonary disease: discriminatory value. Radiology 223: 812–819 29. Lucidarme O, Grenier P A, Cadi M et al 2000 Evaluation of air trapping at CT: comparison of continuous versus suspended-expiration CT techniques. Radiology 216: 768–772 30. Hansell D M, Rubens M B, Padley S P et al 1997 Obliterative bronchiolitis: individual CT signs of small airways disease and functional correlation. Radiology 203: 721–726

CHAPTER

Pulmonary Lobar Collapse: Essential Considerations

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Susan J. Copley

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Mechanisms and causes of lobar collapse Radiographic considerations Computed tomography of lobar collapse Other imaging techniques in lobar collapse Patterns of lobar collapse

Collapse and atelectasis are terms which are often used synonymously and refer to loss of volume within the lung. In North America, the term collapse is often reserved to denote complete loss of volume within an entire lobe or lung1.

MECHANISMS AND CAUSES OF LOBAR COLLAPSE Broadly, lobar collapse can be divided into those due to endobronchial obstruction (either intrinsic or extrinsic) and those without obstruction2,3.The causes of lobar collapse are summarized in Table 17.1.The common causes differ slightly between adults and children. In adults the frequent causes of intrinsic obstruction are tumours and mucus plugs. In the clinical context of a middleaged or elderly smoker, lobar collapse should always be suspected to be due to a bronchogenic carcinoma until proved otherwise. All cell types of bronchogenic carcinoma can potentially cause intrinsic large airway obstruction and produce segmental, lobar or whole lung collapse (Fig. 17.1)2. More rarely, foreign bodies, broncholiths and focal bronchostenosis due to inflammation or trauma may be encountered. In children, causes such as inhaled foreign bodies or mucus plugs are common (Fig. 17.2), with tumours being very rare.

RADIOGRAPHIC CONSIDERATIONS The cardinal radiographic features of lobar collapse are increased opacity of the affected lobe and volume loss. The latter can be inferred by direct and indirect signs. Direct signs of volume loss refer to displacement of interlobar fissures, pulmonary vessels and bronchi, whereas indirect signs include

compensatory shifts of adjacent structures such as hyperinflation of other lobes. The effects of a lobar collapse are often maximal on immediately adjacent structures, e.g. an upper lobe collapse often results in a shift of the superior mediastinum, whereas a lower lobe collapse often demonstrates elevation of the posterior part of the diaphragm in particular. However, the general principles and fundamental radiographic signs are similar for all lobes. A collapsed lobe appears radiographically dense due to a combination of retained secretions or fluid within the lobe and reduction in aeration of the lobe4. However, retained fluid is the dominant process resulting in increased opacity of a partially collapsed lobe, as virtually complete collapse is required to displace sufficient air for the normally radiographically hyperlucent lung to appear dense.

Direct signs of volume loss Displacement of fissures is a reliable feature of lobar collapse, and is generally characteristic depending on the affected lobe5. The pulmonary vessels and bronchi become crowded together in the affected lobe as the lung loses volume. The sign may be one of the earliest seen in lobar collapse and can often be readily appreciated by comparison with previous radiographs. Hilar elevation on the PA chest radiograph is a wellknown sign of upper lobe collapse: the ipsilateral interlobar and lower lobe arteries remain visible as these structures are still outlined by aerated lung. It would seem logical to consider ‘hilar depression’ to be a sign of lower lobe collapse, but some authorities believe the small hilum to be a more accurate description5. This is due to the fact that when a lower lobe collapses, the opaque, collapsed lobe obscures the lower lobe artery that lies within it, and the interlobar artery is usually rotated so the margin is no longer in profile to the frontal X-ray beam. Consequently, it is difficult to recognize the hilum as being depressed and instead, smaller vascular structures are noted at the expected position of the hilum. Occasionally, confusion with a central hilar mass/ adenopathy can arise if the convex margin of an interlobar artery remains visible due to minimal rotation6.

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Table 17.1 CAUSES OF LOBAR COLLAPSE 2,3 Lobar collapse due to endobronchial obstruction • Intrinsic Bronchogenic carcinoma Bronchial carcinoid Adenoid cystic carcinoma Metastases (e.g. breast, renal cell and colonic carcinoma, melanoma, sarcoma) Lymphoma Benign tumours (e.g. lipoma, hamartoma, papillomas, endometriomas) Granulomatous diseases (e.g. sarcoidosis and tuberculosis) Miscellaneous conditions (e.g. aspirated foreign bodies, mucus plugs, gastric contents, malpositioned endotracheal tubes, bronchial torsion or rupture, amyloidosis, Wegener’s granulomatosis) • Extrinsic Hilar or mediastinal lymphadenopathy (commonly due to bronchogenic or breast carcinoma) Mediastinal masses Fibrosing mediastinitis Aortic aneurysms and congenital vascular anomalies Cardiac enlargement

Lobar collapse without endobronchial obstruction • Miscellaneous conditions (e.g. passive collapse due to pleural fluid or pneumothorax, radiation-induced collapse, tumour replacement [bronchiolo-alveolar cell carcinoma])

Figure 17.1 Total left lung collapse. (A) Frontal and (B) lateral chest radiographs. The cause of the collapse is a bronchogenic carcinoma; the endobronchial component is visible as an abrupt cut-off of the left main bronchus. Note the marked displacement of the right lung anteriorly and posteriorly across the midline (arrows). Note the marked anterior hyperlucency of the thorax on the lateral view (B).

As well as vascular reorientation, hilar bronchial alterations also occur. The central large bronchi undergo characteristic changes in position with collapse of either the upper or lower lobe. When either upper lobe collapses significantly, the ipsilateral main bronchus becomes more horizontally orientated than usual, hence the bronchus intermedius and the left lower lobe bronchus swing laterally. Conversely, when either lower lobe collapses, each main bronchus is more vertically orien-

tated than usual, with a medial swing of the bronchus intermedius on the right and the lower lobe bronchus on the left.

Indirect signs of volume loss Compensatory hyperinflation of adjacent lobes occurs with lobar collapse, resulting in fewer vessels per unit volume of lung. It is often easier to detect a paucity of vessels, which are more widely spaced than on the unaffected side, than

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Figure 17.2 Total right lung collapse in a neonate. The patient was ventilated for respiratory distress syndrome and the cause of the total lung collapse was a mucus plug.

subtle increased radiolucency. In isolation, the sign may be due to causes other than lobar collapse and other confirmatory features should be sought before making the diagnosis. The normal lung parenchyma should expand proportionally to compensate for the degree of collapse and often the greater the degree of lobar collapse, the greater the compensatory overinflation. Therefore when small lung volumes are involved, the hyperinflation usually only involves the remainder of the ipsilateral lung, whereas with larger volumes, the contralateral lung may expand across the midline. On a frontal radiograph the lung may expand across the midline superiorly, thus displacing the anterior junctional line to the contralateral side (see Fig. 17.1A). On a lateral view, the anterior medias-



PULMONARY LOBAR COLLAPSE: ESSENTIAL CONSIDERATIONS

tinum appears hyperlucent (see Fig. 17.1B). Displacement of the azygo-oesophageal line and posterior junctional line on the PA radiograph, which denote protrusion of contralateral lung through other weak areas between the oesophagus and vertebral column and the retrocardiac space respectively, may be more difficult to recognize. Although the term ‘mediastinal herniation’ is sometimes used, some authorities emphasize that there is no actual mediastinal defect or hiatus and the sign more accurately denotes displacement of mediastinal structures7. A divergent or parallel pattern of vascular reorientation seen near the hilum has been described in marked upper lobe collapse8.The pattern is seen more commonly on the left than on the right, as a result of the different degree of compensatory overinflation in the superior segment of the ipsilateral lower lobe on each side8. The right middle lobe can also overinflate in compensation, which further explains the lesser degree of overinflation of the superior segment of the right lower lobe. The sign of vascular reorientation can be helpful when unusual patterns of upper lobe collapse are present. Hyperexpansion may also result in a change in position of lung lesions, such as granulomas resulting in the so-called shifting granuloma sign (Fig.17.3). Of particular note, the Luftsichel sign (from German, meaning air crescent) is due to the overinflated superior segment of the ipsilateral lower lobe occupying the space between the mediastinum and the medial aspect of the collapsed upper lobe, resulting in a paramediastinal translucency (Fig. 17.4)9. The sign is more common on the left than the right and is regarded as a typical appearance of left upper lobe collapse9. CT demonstrates the increased paramediastinal lucency to be due to a wedge shape of the collapsed upper lobe, with the apex of the V resulting from tethering of the major fissure by hilar structures (Fig. 17.4B).

Figure 17.3 Shifting granuloma sign. (A) Pre and (B) post right lower lobe collapse.

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Figure 17.4 Luftsichel sign. (A) A left upper lobe collapse demonstrating paramediastinal lucency (arrow). (B) CT shows interposition of aerated lung between the collapse and the mediastinum (arrow). There is also a large right paratracheal node causing some distortion of the SVC.

Mediastinal shift is another indirect sign of volume loss and the degree varies according to the position of the affected lobe. Usually the least mediastinal shift occurs in right middle lobe collapse, whilst the greatest shift, particularly of the inferior mediastinum, is seen with lower lobe collapse. The amount of mediastinal shift due to upper lobe collapse is often dependent on the chronicity: in acute upper lobe collapse there is often little shift, whereas in chronic upper lobe volume loss with fibrosis, the shift may be greater. The position of the trachea may be a useful indicator of superior mediastinal shift as it should be central in the superior mediastinum between the anterior ends of the clavicles or slightly deviated to the right by the aortic arch. Inferiorly within the mediastinum, anywhere between one-half and one-fifth of the cardiac outline normally lies to the right of the midline and greater or lesser variations indicate mediastinal shift. However, because of the wide variation in normal subjects, displacement of the cardiac outline may be more difficult to assess than changes in position of the trachea. The hemidiaphragms may be elevated in lobar collapse, particularly involving the left upper lobe and to a lesser extent the right upper and both lower lobes. However, the sign is of limited value because the position of the right hemidiaphragm is highly variable (0–3 cm higher than the left on the frontal chest radiograph). A useful ancillary sign of upper lobe collapse (or a combination of right upper and middle lobe collapse) is a juxtaphrenic peak of the diaphragm (Fig. 17.5)10. The sign refers to a small triangular density at the highest point of the dome of the hemidiaphragm, due to the anterior volume loss of the affected upper lobe resulting in traction and reorientation of an inferior accessory fissure11,12. Reduction in the volume of a hemithorax may result in relative reduction of the spaces between the ribs by comparison to the unaffected side. Rib crowding or approximation may be recognizable on the frontal radiograph in cases of chronic lobar collapse, but in acute collapse it may be more difficult to appreciate. Furthermore, the sign is considered to be unreli-

Figure 17.5 Juxtaphrenic peak sign. A small triangular density (arrow) is seen in a left upper lobe collapse. The sign is due to reorientation of an inferior accessory fissure.

able as patient rotation and minor degrees of scoliosis may result in apparent rib crowding.

Ancillary features of lobar collapse Occasionally the cause of a lobar collapse may be apparent and an endobronchial lesion may be clearly demonstrated radiographically (Fig. 17.1A). However, although the actual endobronchial component is often not directly visualized, lobar collapse due to a central obstructing bronchogenic carcinoma is most likely when Golden’s S sign is seen (Fig. 17.6). The sign refers to the S shape (or more accurately, reverse S on the right) of the fissure due to the combination of collapse and mass centrally resulting in a focal convexity with a concave outline peripherally. Although the sign was originally described in the right upper lobe, it can be seen in any lobe5,13. The CT equivalent is discussed later. Generally, absence of air

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PULMONARY LOBAR COLLAPSE: ESSENTIAL CONSIDERATIONS

Figure 17.6 Golden’s S sign. A right upper lobe collapse demonstrating peripheral concavity and central convexity (arrows) due to an underlying bronchogenic carcinoma resulting in a reverse S shape.

bronchograms within the affected lobe should also raise the suspicion of a central obstructing lesion as there is absorption of air from both the lung parenchyma and airways. The sign may be useful to distinguish a central obstructing mass from a consolidative process such as bacterial pneumonia (Fig. 17.7). The rare important caveats are when a mass results in only partial obstruction of the airways or in cases of acute bronchopneumonia where the airways are filled with an inflammatory exudate. However, the sign is not as reliable on CT, and often distal air bronchograms are visible in part of a collapsed lobe due to a central neoplasm (Fig. 17.8).

Figure 17.8 CT of a collapsed right upper lobe due to a squamous cell carcinoma. Note the peripheral air bronchograms (arrow) in (A) despite a central obstructing mass with amorphous calcification (B). There is a convex border of the collapsed lobe (arrows) (B) which is the CT equivalent of Golden’s S sign.

COMPUTED TOMOGRAPHY OF LOBAR COLLAPSE CT has become an invaluable method for the investigation of patients with lobar collapse. The obvious benefits are a lack of superimposition of overlying structures with the added advantage of demonstration of anatomical structures in the axial and, with computer reformatting, coronal and sagittal planes. Not only does CT aid the understanding of the radiographic appearances of lobar collapse, it also provides invaluable information about the cause which may not be apparent on chest radiography. The most common indication for CT in adults with lobar collapse is to identify an endobronchial or compressing lesion.

Technique

Figure 17.7 Air bronchograms in a collapsed and consolidated right lower lobe. The sign can be helpful in excluding a central obstructing mass and in this case the cause was a bacterial pneumonia.

Careful attention to CT technique is sometimes required to accurately demonstrate an obstructing lesion resulting in lobar collapse. The old recommendations using single slice CT14 have been superseded by techniques using helical and now multidetector CT (MDCT). Such systems can often provide high resolution images from the same data acquisition as used for other purposes with a saving in radiation dose. The facility to reconstruct and reformat volumetric data has resulted

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in advancements in the display of tracheobronchial anatomy. Three-dimensional (3D) and multiplanar (2D) images provide an extremely useful adjunct to axial images15.

Utility In some cases, the aetiology of lobar collapse can be determined from the patient’s clinical history, examination, and chest radiographic features. Using fibre-optic bronchoscopy as the reference standard, CT is clearly more sensitive than chest radiography for the detection of an obstructing carcinoma16. Reported sensitivities for detection by CT range from 83 to 100%17–20 but generally, when an endobronchial lesion is sufficiently large to cause lobar collapse, CT is a reliable method for detection2,16. False-positive diagnoses may be due to bronchial strictures, plugs of mucus or secretions and compression by large pleural effusions2,3,16. CT is not histologically specific, however, as bronchogenic carcinoma, endobronchial metastases, bronchial adenomas and lymphoma may all have similar appearances2. The accuracy of CT is, to some extent, dependent on technique and it may be more difficult to demonstrate endobronchial lesions in the right middle lobe and lingular bronchi owing to their oblique orientation relative to the axial plane. This is much less of a problem with MDCT. Accurate delineation of a tumour mass from a surrounding collapsed lobe may be problematical, but collapsed lung usually enhances to a greater degree than tumour with dynamically contrast-enhanced CT (Fig. 17.9)21. The difference in attenuation value is maximal between 40 s and 2 min after a bolus injection of contrast medium21. In practice, the distinction between tumour and collapsed lung may not be important and the technique is reserved for cases where more accurate delineation is necessary for treatment purposes, e.g. radiotherapy planning. Golden’s S sign on chest radiography has a CT equivalent that may be helpful in identifying an obstructing tumour22,23. Usually, a collapsed lobe is associated with concavity of the

Figure 17.9 CT of right upper lobe collapse due to bronchogenic carcinoma. Note how the attenuation of the necrotic tumour is lower than the adjacent collapsed lung which enhances with intravenous contrast medium.

adjacent fissure and a localized convexity is highly suggestive of an underlying mass (see Fig. 17.8). The sign is not entirely specific, but it is strongly indicative of a bronchogenic carcinoma. Unlike the frontal chest radiograph, in which the S sign is only helpful in the right upper lobe and to a lesser extent the right and left lower lobes, the S sign can be applied to all lobes on CT. Another CT sign that is highly suggestive of an obstructing lesion causing lobar collapse is the CT mucous bronchogram sign24. Histopathologically, the lobar and segmental bronchi are filled with inspissated secretions and are usually dilated. The airways are optimally demonstrated as tubular, low attenuation branching structures within the enhancing collapsed lobe following intravenous contrast enhancement (Fig. 17.10).

Figure 17.10 Left lung collapse. (A, B) Contrast-enhanced CT sections of whole lung collapse due to a squamous cell carcinoma in the left main bronchus (arrow in A). There is also a left pleural effusion and a small pericardial effusion. Note the low-attenuation areas relative to the densely enhancing left lower lobe parenchyma (B) which represent mucus-filled airways—the CT mucous bronchogram sign.

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PULMONARY LOBAR COLLAPSE: ESSENTIAL CONSIDERATIONS

Obstructing lesions such as bronchogenic carcinoma or benign causes, including tuberculous bronchostenosis, should be considered. The sign may also result from excessive mucus production combined with decreased mucociliary function in conditions such as allergic bronchopulmonary aspergillosis, asthma and cystic fibrosis25. CT also has a role in complicated or atypical lobar collapse as their appearances may be confusing on chest radiography. In particular, combined right middle lobe and right upper lobe collapse may be difficult to diagnose on chest radiography when the collapse is nearly complete26. CT is useful for demonstrating mediastinal anatomy and provides information about mediastinal lymph nodes and the staging of a tumour causing lobar collapse.Additional signs of lobar collapse, such as compensatory overinflation and the Luftsichel sign (described above), are also well demonstrated, providing explanations for the radiographic appearances of lobar collapse27,28.

Potential pitfalls The increased sensitivity of CT by comparison with radiography means that the presence of an air bronchogram within a lobar collapse does not necessarily exclude a central obstructing lesion (see Fig. 17.8.)24. In this context, an air bronchogram may be seen in the peripheral part of a collapsed lobe due to collateral air drift or tumour necrosis16. Similarly, a proximal obstructing lesion may not cause complete lobar collapse when a fissure is incomplete allowing ventilation by collateral air drift29. Occasionally the parenchyma and airways become filled with fluid owing to the presence of a central obstructing lesion with little or no associated volume loss, and the lobe may even be expanded giving rise to the appearance termed ‘drowned lobe’. The CT equivalent of the Golden’s S sign is particularly well demonstrated with right-sided lobar collapse and, on the left, care should be taken in interpretation owing to the fact that normal mediastinal structures may mimic a mass (e.g. thoracic aorta)22 (Fig. 17.11).

Figure 17.11 Left lower lobe collapse. Contrast-enhanced CT showing a tight left lower lobe collapse. Normal mediastinal structures (particularly left-sided) may cause a focal bulge in the contour of a lobar collapse (in this case by the well opacified descending thoracic aorta) and should not be confused with a Golden’s S sign due to tumour.

The accurate determination of the reversibility and chronicity of a lobar collapse may be problematical. Relatively acute collapses may show apparent bronchiectatic dilatation of the airways and may mimic a long-standing irreversible event (Fig. 17.12); a meaningful evaluation of the airways in the context of a lobar collapse is therefore often difficult.

OTHER IMAGING TECHNIQUES IN LOBAR COLLAPSE Magnetic resonance imaging (MRI) has been largely surpassed by CT in the investigation of lobar collapse owing to

Figure 17.12 Resolution of left lower lobe collapse. (A) An initial high-resolution CT of a young female patient with symptoms of recurrent respiratory tract infections shows a collapsed left lower lobe with possible bronchiectatic airways, raising the possibility of chronicity. (B) Follow-up conventional CT at the same level several months later shows complete resolution of the left lower lobe collapse and normal airways. This case illustrates the difficulty in making an accurate assessment of the airways in patients with lobar collapse.

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the superior spatial resolution of the latter. In particular, endobronchial tumours and smaller bronchi are less well demonstrated by MRI than CT30. Studies have investigated the ability of MRI to differentiate a tumour mass from postobstructive collapse by utilizing differences in signal characteristics31–33. Sometimes the distinction can be made on T1-weighted images, but it is generally accepted that T2-weighted images are superior as the tumour is of lower signal intensity than the obstructed lung which has a higher water content. On ultrasound of a large pleural effusion, the underlying collapsed lung is often visible as a hyperechoic wedge-shaped area within hypo-echoic or anechoic fluid. In practice, the main utility of ultrasound is to readily distinguish pleural effusion from a collapsed and consolidated lung when radiographic appearances are equivocal. On positron emission tomography (PET), a collapsed lobe often demonstrates less uptake of [18F]fluorodeoxyglucose than tumour. By comparison with CT, PET may therefore provide more accurate delineation of tumour from postobstructive collapsed lung, which may be useful in treatment with radiotherapy34.

Figure 17.13 Right upper lobe collapse. Typical example of a collapsed right upper lobe demonstrating the slightly concave inferior border of the opacified lung due to the horizontal fissure.

PATTERNS OF LOBAR COLLAPSE Right upper lobe collapse On the frontal radiographic view of a right upper lobe collapse, the collapsed lobe forms increased density at the apex of the hemithorax adjacent to the right side of the mediastinum, with the elevated horizontal fissure resulting in a concave inferior outline depending on the degree of collapse (Fig. 17.13). Even in cases where there is no obstructing lesion, there is often a small convexity at the hilum due to the pulmonary veins and artery where the apex of the lobe is attached to the hilum. On the lateral view, the horizontal and oblique fissure approximate and are both displaced superiorly and medially with the collapsed lobe forming a superior ill-defined wedgeshaped density. In cases where the collapse is very severe, the horizontal fissure parallels the mediastinum and appearances may simulate an apical cap of pleural fluid (Fig. 17.14) or mediastinal widening on the frontal radiograph (Fig. 17.15). There is also usually compensatory hyperinflation of the right middle and lower lobes, resulting in elevation and a more horizontal course of the lower lobe pulmonary artery and right main bronchus. The vascular reorientation can be recognized on the frontal view, but the right main and lower lobe bronchial displacement can be difficult to appreciate on both the frontal and lateral view. On CT the right upper lobe forms a triangular density with the base anteriorly against the chest wall and the apex at the hilum (Fig. 17.16). A focal bulge of the lateral border usually indicates an underlying mass. Compensatory hyperinflation of not only the right middle and right lower lobes but also the left upper lobe is often more easily appreciated on CT.

Left upper lobe collapse The cardinal features of left upper lobe collapse are fundamentally different from right upper lobe collapse as there is very rarely a horizontal fissure on the left. Consequently, the main

Figure 17.14 Right upper lobe collapse. An example of right upper lobe collapse mimicking an apical cap of fluid (arrow).

direction of volume loss is anteriorly and medially rather than superiorly, and the entire oblique fissure is displaced in that direction parallel to the chest wall on the lateral view. On the frontal view the signs may be variable depending on the degree of collapse, but there is a ‘veil-like’ increased density of the whole of the affected hemithorax in most cases. The increased density is often greatest at the hilum and it gradually fades out laterally, superiorly, and inferiorly without the clear inferior demarcation of the horizontal fissure as seen in right upper lobe collapse.The difference in transradiancy may be relatively subtle and therefore overlooked by the unwary. The other features that aid diagnosis on the frontal view are loss of the normal silhouette of structures

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PULMONARY LOBAR COLLAPSE: ESSENTIAL CONSIDERATIONS

Figure 17.15 Tight right upper lobe collapse. Note how the collapsed lobe (due to a central bronchogenic carcinoma) results in increased right paramediastinal density.

Figure 17.16 CT of right upper lobe collapse. The collapsed lobe forms a triangular wedge of soft tissue anteriorly in the right hemithorax.

adjacent to the collapse, such as the left heart border, mediastinum, and aortic arch, as these structures are no longer adjacent to aerated lung. There is some variability in which outlines are obscured depending on the degree of collapse. In cases of relatively less severe collapse, the left heart border, left mediastinal outline and aortic knuckle are obscured (see Fig. 17.5), whereas in more severe cases the apical segment of the left lower lobe is hyperexpanded superiorly adjacent to the aortic arch and somewhat paradoxically the aortic knuckle outline is therefore visible in more severe cases as it is adjacent to aerated lung (Fig. 17.17A). The Luftsichel sign (described above; see Fig. 17.4) is a particular manifestation of the hyperexpansion, and literally describes an ‘air crescent’ which may be seen between the aortic arch and the medial border of the collapse. On the lateral view the anterior outline of the ascending thoracic aorta can be seen with unusual clarity and this is due to compensatory hyperinflation of the right upper lobe across the midline and rotation of the medi-

Figure 17.17 Left upper lobe collapse. (A) A typical example of left upper lobe collapse demonstrating increased angulation between the left main bronchus and the lower lobe bronchus (arrow) on the frontal view. The aortic knuckle is visible in this example due to compensatory hyperinflation of the left lower lobe. (B) The lateral view demonstrates anterior displacement of the oblique fissure. Note the increased retrosternal lucency (see Fig. 17.18).

astinum so the anterior aspect of the aorta is outlined by aerated lung tangential to the X-ray beam (Fig. 17.17B). This feature is often readily appreciated on CT (Fig. 17.18). On the frontal radiograph the left main bronchus is reorientated and has a more horizontal course than usual. The superior displacement of this structure results in angulation between the left main bronchus and the left lower lobe bronchus (Fig. 17.17A). The CT appearances of left upper lobe collapse are similar to that of the right upper lobe with a triangular soft tissue density, the apex at the origin of the upper lobe bronchus and the base against the anterior chest wall, adjacent to the left border of the mediastinum. However, in the left upper lobe the lingular segment is seen as a density closely opposed to the left heart border. Rarely, left upper lobe collapse may mimic right upper lobe collapse (Fig. 17.19). The appearance is due to collapse of the apicoposterior and anterior segments of the left upper lobe with sparing of the lingular portion resulting in a concavity to the inferior border of the collapse, even in the absence of a left

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Figure 17.18 Left upper lobe collapse. Intravenous contrastenhanced CT of left upper lobe collapse shows increased wedge-shaped density of the left upper lobe adjacent to the mediastinum. Note the displacement of the right lung across the midline anteriorly, resulting in retrosternal hyperlucency and increased clarity of the anterior ascending thoracic aorta on the lateral view (see Fig. 17.17B).

collapsed lobe lies obliquely in the chest, more parallel with the major fissure, the only sign on the frontal radiograph may be indistinctness of a portion of the right atrial border (Fig. 17.21). By comparison, the triangular density of the collapsed right middle lobe is relatively easy to identify on the lateral view, with approximation of the minor and inferior portion of the major fissure, the apex of the triangle being at the hilum (Fig. 17.21B). In increasingly severe collapse the triangular shape is less marked as the fissures become almost parallel with only a thin wedge of density separating them. The CT appearances are characteristically of a triangularshaped density of varying size adjacent to the heart border. Depending on the orientation of the collapse, only a small portion may be identified on each section as the collapse represents a relatively flat sheet of tissue. The so-called middle lobe syndrome refers to a collapsed right middle lobe with bronchiectasis due to a focal bronchostenosis secondary to pulmonary tuberculosis. Although in theory any lobe may be affected, the middle lobe is the most common, resulting in characteristic CT features (Fig. 17.23).

Right and left lower lobe collapse minor fissure5. Apart from being on the left, isolated collapse of the lingula has a very similar appearance to right middle lobe collapse (Fig. 17.20).

Right middle lobe collapse The features of right middle lobe collapse may be extremely subtle on the frontal view and consequently easy to overlook. The collapsed lobe lies adjacent to the right heart border and there is loss of the silhouette of this structure to a variable degree (Fig. 17.21). There may or may not be a recognizable increase in density depending on the orientation of the collapse relative to the X-ray beam. When the collapse is orientated roughly parallel to the beam or if the patient is in a lordotic position, a triangular, sail-shaped density may be seen adjacent to the heart border (Fig. 17.22). However, if the

The features of right and left lower lobe collapse are very similar and will be considered together. In collapse of the lower lobes, the oblique fissure is displaced posteriorly and medially, and the collapsed lobe lies in the posteromedial portion of the chest, a feature readily appreciated on CT (see Fig. 17.11). On the frontal radiograph, the collapsed lower lobes usually form a triangular density behind the heart (Fig. 17.24). The medial portion of the hemidiaphragm may be obscured as it is no longer outlined by aerated lung (Fig. 17.25), but if the inferior pulmonary ligament is incomplete and does not attach to the diaphragm, the medial contour of the diaphragm may still be visualized. On the lateral radiograph, a posterior portion of the hemidiaphragm may not be seen (Fig. 17.24B), but in more severe collapse the contour may reappear as it becomes outlined by aerated lung from the

Figure. 17.19 Atypical left upper lobe collapse. (A) The frontal radiograph demonstrates the inferior concave border of the collapsed lobe and resembles a right upper lobe collapse. (B, C) CT images show increased triangular density to the left of the mediastinum (B), which does not extend along the left heart border (C), a feature usually seen in left upper lobe collapse. The appearance is due to sparing of the lingular segments.

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PULMONARY LOBAR COLLAPSE: ESSENTIAL CONSIDERATIONS

Figure 17.20 Lingular collapse. (A) Frontal view of isolated collapse of the lingular segments of the left upper lobe showing loss of clarity of the left heart border and a raised hemidiaphragm. (B) The similarity to a right middle lobe collapse can be appreciated on the lateral view.

Figure 17.21 Right middle lobe collapse. (A) Frontal view of a typical example showing loss of clarity of the right heart border. (B) The lateral view shows the wedge-shaped density extending anteriorly from the hilum.

Figure 17.22 Right middle lobe collapse. An example showing a triangular-shaped density adjacent to the right heart border.

Figure 17.23 Middle lobe syndrome. High-resolution CT showing right middle lobe collapse and bronchiectasis due to previous tuberculous infection.

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Figure 17.25 Left lower lobe collapse. A typical appearance of left lower lobe collapse resulting in a triangular density behind the heart (arrowheads). The contour of the medial left hemidiaphragm is lost.

Figure 17.24 Right lower lobe collapse. (A) Frontal view of an example of right lower lobe collapse demonstrating a triangular density which does not obscure the right hemidiaphragm silhouette. (B) The lateral radiograph shows the typical features of increased density of the posterior costophrenic angle and loss of the silhouette of the right diaphragm posteriorly.

hyperexpanded upper lobe. In addition, the vertebral column appears progressively denser inferiorly in lower lobe collapse (Fig. 17.24B), whereas normally the converse is true. On the frontal radiograph the lower lobe pulmonary artery is usually not seen in lower lobe collapse as it is no longer outlined by aerated lung (Fig. 17.26). The major airways, including the right and left main bronchi, are also displaced more vertically in lower lobe collapse and often the relevant aircontaining bronchus can be identified as leading directly into the triangular density of the collapsed lobe. There are several features involving the upper mediastinum which are sometimes helpful in diagnosing lower lobe collapse35. The first of these is the ‘superior triangle sign’ and refers to a triangular density to the right of the mediastinum seen in right lower lobe collapse due to displacement of anterior junctional structures36 (Fig. 17.26). The appearance should not be confused with right upper lobe collapse. The ‘flat waist sign’ is seen in extensive

collapse of the left lower lobe and describes flattening of the contours of the aortic knuckle and main pulmonary artery due to cardiac rotation and displacement to the left37. Third, the outline of the superior aortic knuckle may be lost in severe left lower lobe collapse35. On CT, the collapsed lower lobes form a triangle of soft tissue density posteriomedially in the thorax, adjacent to the spine. On the left, the collapsed lower lobe is seen to drape over the descending aorta, giving a focal convexity to the lateral border, a feature which potentially can cause confusion with an underlying mass on an unenhanced CT (Fig. 17.11).

Whole lung collapse Collapse of an entire lung results in complete opacification or ‘white-out’ of the affected hemithorax. In adults, the cause is often an obstructing neoplasm in the right or left main bronchi (see Fig. 17.1). There is marked volume loss with compensatory hyperinflation of the contralateral lung across the midline. The cardinal feature of volume loss can help discriminate between collapsed lung and a large pleural effusion, the latter usually resulting in mediastinal shift to the contralateral side. The lateral radiograph shows accentuation of the retrosternal space as the displacement of the contralateral lung is greatest anteriorly (see Fig. 17.1). By comparison, the opacity of the hemithorax is more uniform on the lateral view in large pleural effusion and may be a useful discriminating feature in equivocal cases.

Combinations of lobar collapse Occasionally various combinations of lobar collapse occur. Collapse of the right middle and right lower lobes is often due to an obstructing lesion in the bronchus intermedius (Fig. 17.27). The features are similar to right lower lobe collapse with the exception that the opacity extends laterally to the costophrenic

CHAPTER 17



PULMONARY LOBAR COLLAPSE: ESSENTIAL CONSIDERATIONS

Figure 17.26 Superior triangle sign. (A) An initial image shows the normal appearances (note the lower lobe artery is clearly visible). (B) The subsequent image shows a right lower lobe collapse demonstrating the superior triangle sign (arrow) (which should not be confused with a right upper lobe collapse). The lower lobe artery can no longer be seen.

Figure 17.27 Combined right middle and right lower lobe collapse. (A) On the frontal view the increased density extends to the right costophrenic angle. (B) On the lateral view the increased density also extends from the anterior to the posterior chest wall. The cause in this case was a bronchogenic carcinoma obstructing the bronchus intermedius.

angle on the frontal view and from the front to the back of the hemithorax on the lateral view5 (Fig. 17.27B). Collapse of the right upper and right middle lobes is more unusual as these lobes do not have a common bronchial origin which spares the lower lobe. In adults the cause is often a carcinoma which obstructs one bronchus and causes extrinsic compression of the other due to mass

effect. Combined collapse of the right upper and right middle lobes results in an appearance very similar to left upper lobe collapse on both frontal and lateral radiographs and CT38. Both bilateral lower lobe and upper lobe collapse are exceedingly rare and may occur as a result of metachronous bronchial neoplasms or mucous plugging (Fig. 17.28).

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Figure 17.28 Bilateral lower lobe collapse. Bilateral triangular densities are seen with obscuration of the medial portions of the hemidiaphragms. The cause was mucous plugging.

REFERENCES 1. Tuddenham W J 1984 Glossary of terms for thoracic radiology: recommendations of the Nomenclature Committee of the Fleischner Society. Am J Roentgenol 143: 509–517 2. Naidich D P, McCauley D I, Khouri N F, Leitman B S, Hulnick D H, Siegelman S S 1983 Computed tomography of lobar collapse: 1. Endobronchial obstruction. J Comput Assist Tomogr 7: 745–757 3. Naidich D P, McCauley D I, Khouri N F, Leitman B S, Hulnick D H, Siegelman S S 1983 Computed tomography of lobar collapse: 2. Collapse in the absence of endobronchial obstruction. J Comput Assist Tomogr 7: 758–767 4. Stein L A, Vidal J J, Hogg J C, Fraser R G 1976 Acute lobar collapse in canine lungs. Invest Radiol 11: 518–527 5. Proto A V, Tocino I 1980 Radiographic manifestations of lobar collapse. Semin Roentgenol 15: 117–173 6. Proto AV 1984 The chest radiograph: anatomic considerations. Clin Chest Med 5: 213–246 7. Lodin H 1957 Mediastinal herniation and displacement studied by transversal radiography. Acta Radiol 48: 337–350 8. Proto A V, Moser E S Jr 1987 Upper lobe volume loss: Divergent and parallel patterns of vascular reorientation. RadioGraphics 7: 875–887 9. Webber M, Davies P 1981 The Luftsichel: an old sign in upper lobe collapse. Clin Radiol 32: 271–275 10. Kattan K R, Eyler W R, Felson B 1980 The juxtaphrenic peak in upper lobe collapse. Semin Roentgenol 15: 187–193 11. Cameron D C 1993 Juxtaphrenic peak (Katten’s sign) is produced by rotation of an inferior accessory fissure. Australas Radiol 37: 332–335 12. Davis S D, Yankelevitz D F, Wand A, Chiarella D A 1996 Juxtaphrenic peak in upper and middle lobe volume loss: assessment with CT. Radiology 198: 143–149 13. Golden R 1925 The affect of bronchostenosis upon the roentgen-ray shadows in carcinoma of the bronchus. Am J Roentgenol Radiat Ther 13: 21–30 14. Naidich D P, Webb W R, Müller N L, Krinsky G A, Zerhouni E A, Siegelman S S 1999 Computed tomography and magnetic resonance of the thorax, 3rd edn. Lippincott–Raven, Philadelphia

15. LoCicero J, Costello P, Campos C T et al 1996 Spiral CT with multiplanar and three-dimensional reconstructions accurately predicts tracheobronchial pathology. Ann Thorac Surg 62: 818–822 16. Woodring J H 1988 Determining the cause of pulmonary atelectasis: a comparison of plain radiography and CT. Am J Roentgenol 150: 757–763 17. Henschke C I, Davis S D, Auh Y et al 1987 Detection of bronchial abnormalities: comparison of CT and bronchoscopy. J Comput Assist Tomogr 11: 432–435 18. Webb W R, Gamsu G, Speckman J M 1983 Computed tomography of the pulmonary hilum in patients with bronchogenic carcinoma. J Comput Assist Tomogr 1983;7:219–225. 19. Naidich D P, Lee J-J, Garay S M, McCauley D I, Aranda C P, Boyd A D 1987 Comparison of CT and fibreoptic bronchoscopy in the evaluation of bronchial disease. Am J Roentgenol 148: 1–7. 20. Mayr B, Ingrisch H, Häussinger K, Huber R M, Sunder-Plassmann L 1989 Tumours of the bronchi: role of evaluation with CT. Radiology 172: 647–652 21. Onitsuka H, Tsukuda M, Araki A, Murakami J, Torii Y, Masuda K 1991 Differentiation of central lung tumor from postobstructive lobar collapse by rapid sequence computed tomography. J Thorac Imaging 6: 28–31 22. Reinig J W, Ross P 1984 Computed tomography appearance of Golden’s “S” sign. J Comput Assist Tomogr 8: 219–223 23. Khoury M B, Godwin J D, Halvorsen R A, Putman C E 1985 CT of obstructive lobar collapse. Invest Radiol 20: 708–716 24. Woodring J H 1988 The computed tomography mucous bronchogram sign. J Comput Assist Tomogr 12: 165–168 25. Glazer H S, Anderson D J, Sagel S S 1989 Bronchial impaction in lobar collapse: CT demonstration and pathologic correlation. Am J Roentgenol 153: 485–488 26. Saida Y, Itai Y, Kujiraoka Y, Tohno E, Shimizu H T 1997 Bronchoarterial inversion: radiographic–CT correlation in combined right middle and lower lobe collapse. J Thorac Imaging 12: 59–63 27. Flanagan J J, Flower C D, Dixon A K 1982 Compensatory emphysema shown by computed tomography. Clin Radiol 33: 553–554 28. Blankenbaker D G 1998 The Luftsichel sign. Radiology 208: 319–320 29. Woodring J H, Reed J C 1996 Radiographic manifestations of lobar atelectasis. J Thorac Imaging 11: 109–144 30. Mayr B, Heywang S H, Ingrisch H, Huber R M, Häussinger K, Lissner J 1987 Comparison of CT with MR imaging of endobronchial tumors. J Comput Assist Tomogr 11: 43–48 31. Shioya S, Haida M, Ono Y, Fukuzaki M, Yamabayashi H 1988 Lung cancer: differentiation of tumor, necrosis, and atelectasis by means of T1 and T2 values measured in vitro. Radiology 167: 105–109 32. Herold C J, Kuhlman J E, Zerhouni E A 1991 Pulmonary atelectasis: signal patterns with MR imaging. Radiology 178: 715–720 33. Bourgouin P M, McLoud T C, Fitzgibbon J F et al 1991 Differentiation of bronchogenic carcinoma from postobstructive pneumonitis by magnetic resonance imaging: histopathologic correlation. J Thorac Imaging 6: 22–27 34. Nestle U, Walter K, Schmidt S et al 1999 18F-deoxyglucose positron emission tomography (FDG-PET) for the planning of radiotherapy in lung cancer: high impact in patients with atelectasis. Int J Radiat Oncol Biol Phys 44: 593–597 35. Kattan K R 1980 Upper mediastinal changes in lower lobe collapse. Semin Roentgenol 15: 183–186 36. Kattan K R, Felson B, Holder L E, Eyler W R 1975 Superior mediastinal shift in right lower lobe collapse: the “upper triangle sign.” Radiology 116: 305–309 37. Kattan K R, Wiot J F 1976 Cardiac rotation in left lower lobe collapse: “the flat waist sign.” Radiology 118: 275–279 38. Saterfiel J L, Virapongse C, Clore F C 1988 Computed tomography of combined right upper and middle lobe collapse. J Comput Assist Tomogr 12: 383–387

CHAPTER

Pulmonary Neoplasms

18

Simon Padley and Sharyn L. S. MacDonald

• • • • • • •

Bronchial carcinoma Pulmonary sarcoma and other primary malignant neoplasms Benign pulmonary tumours Benign lymphoproliferative disorders Malignant lymphoproliferative disorders Metastases Evaluation of the solitary pulmonary nodule

such as the inappropriate secretion of antidiuretic hormone or a peripheral neuropathy, are the cardinal symptoms at a stage when lobectomy or pneumonectomy may be curative; whereas hoarseness, chest pain, brachial plexus neuropathy and Horner’s syndrome (Pancoast’s tumour), superior vena caval obstruction, dysphagia and the problems of pericardial tamponade indicate invasion of the mediastinum or chest wall, and a poorer prognosis.

Early diagnosis

BRONCHIAL CARCINOMA Lung cancer is the most common cause of cancer-related death in both men and women1,2.Tobacco smoke is the most important causative agent imparting a 20–30-fold increased risk in smokers compared to non-smokers. Other risk factors include passive smoking3, exposure to inorganic substances such as asbestos, nickel and arsenic, interstitial pulmonary fibrosis and radiotherapy.

Pathology The World Health Organization (WHO) classification1 divides bronchial carcinoma into several histological subtypes. Four major cell types: adenocarcinoma, squamous cell carcinoma, large cell carcinoma and small cell carcinoma account for 95% of cases. Of the non-small cell carcinomas, adenocarcinoma accounts for 30–35% of cases. Its relative incidence is rising; it is now the predominant histological subtype in many countries4. The relative incidence of bronchiolo-alveolar carcinoma, which is a subtype of adenocarcinoma, is also increasing as smoking declines. In comparison, the relative incidence of squamous cell carcinoma (30–35% of cases) is decreasing. Large cell carcinoma accounts for 10–15% of cases. Small cell carcinoma accounts for 20–30% of cases.

Clinical presentation Clinical features vary with cell type5 and extent of disease. Approximately 25% of patients are asymptomatic at the time of diagnosis, following the discovery of an abnormality on chest radiograph or computed tomography (CT). Pneumonia is the other common presentation. Cough, wheeze, haemoptysis, symptoms of pneumonia and paraneoplastic syndromes,

Late presentation is one of the factors that have contributed to the lack of significant improvement in survival rates over the past 30 years, despite advances in detection methods and treatments. Median survival from diagnosis has remained at 6–12 months and overall 5-year survival is poor, approximately 5–15%6,7. No study has described definite benefit from screening for lung cancer. Recent large CT studies have demonstrated increased lung cancer detection in at-risk populations but many questions remain unanswered. Most importantly, there is no current evidence that screening confers a disease-specific survival benefit. In an effort to provide definitive evidence, a large-scale trial (National Lung Cancer Screening Trial [USA]) began in 2002 and is due to continue until 2009, after which the findings will be reported. This is a study of overall and comparative utility of chest radiography and spiral CT for lung cancer screening and has recruited 50 000 patients.

Imaging techniques Although lung cancers are frequently detected on chest radiograph, the chest radiograph is of limited use in the evaluation and staging of lung cancer. CT is a more sensitive test for the detection of lung cancer, and is the imaging investigation most widely used to evaluate the primary tumour and the extent of intrathoracic and regional extrathoracic disease. Magnetic resonance imaging (MRI) may provide additional information in selected cases when mediastinal or chest wall invasion is suspected8. Positron-emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) has become a very useful tool in lung cancer staging. It has been found to increase the accuracy of preoperative staging, particularly when used in conjunction with CT (PET–CT)9.

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Imaging features The thoracic imaging features of bronchial carcinoma are discussed under three headings: peripheral tumours; central tumours (arising in a large bronchus at or close to the hilum); and staging intrathoracic spread of bronchial carcinoma.

Peripheral tumours Approximately 40% of bronchial carcinomas arise beyond the segmental bronchi, and in 30% a peripheral mass is the sole radiographic finding10 (Fig. 18.1). Tumour shape and margins Tumours at the lung apex (Pancoast’s tumours, superior sulcus tumours) may resemble apical pleural thickening; however, the majority of peripheral lung cancers are approximately spherical or oval in shape. Lobulation, a sign that indicates uneven growth rates in different parts of the tumour, is common. Occasionally, a dumb-bell shape is encountered or two nodules are seen next to one another. The term corona radiata is used to describe numerous fine strands radiating into the lung from a central mass, sometimes with transradiant lung parenchyma between these strands11. While not specific, this sign is highly suggestive of bronchial carcinoma (Fig. 18.2). Absolutely spherical, sharply defined, smooth-edged nodules due to carcinoma of the lung are rare. A peripheral line shadow or ‘tail’ may be seen between a peripherally located mass lesion and the pleura12, a phenomenon that occurs in both benign and malignant lesions. When associated with carcinoma of the lung, the ‘tail’ probably represents either plate-like atelectasis secondary to bronchial obstruction beyond the mass, or septal oedema due to lymphatic obstruction. Although the edges of a tumour are frequently well defined, some peripheral cancers, notably adenocarcinoma and bronchiolo-alveolar carcinoma, have ill-defined edges similar to pneumonia (Fig. 18.3). Cavitation may be identified in tumours of any size (Fig. 18.4) and is best demonstrated by CT (Fig. 18.5). Squamous cell

Figure 18.1 Bronchial carcinoma in the left lower lobe showing typical rounded, slightly lobular configuration. The mass shows a notch posteriorly.

carcinoma is the most likely cell type to show cavitation. The walls of the cavity are of irregular thickness and may contain tumour nodules, but sometimes the wall has smooth inner and outer margins. The cavity wall is usually 8-mm thick or greater. Fluid levels are common. Calcification within bronchogenic carcinomas is rarely seen on chest radiograph but is identified on CT in 6–10% of cases13,14. Some foci of calcification represent pre-existing calcified granulomatous disease engulfed by tumour (Fig. 18.6). However, amorphous or cloudlike calcification consistent with dystrophic tumour calcification is seen in a significant proportion (Fig. 18.7). Most calcified tumours are large with a diameter of 5 cm or more, but calcification can also be seen in small peripheral tumours. Other findings Air bronchograms and bubble-like lucencies or pseudocavitation may be seen within lung cancers, in particular with bronchiolo-alveolar carcinoma and adenocarcinoma15. Occasionally, dilated mucus-filled bronchi (bronchocele, mucocele, mucoid impaction) are seen distal to a carcinoma obstructing a segmental or subsegmental bronchus16. Ground-glass attenuation may be seen as a component of nodules and is associated with a greater risk of malignancy than that of purely solid nodules. It is more commonly associated with bronchiolo-alveolar carcinoma17, which may present as a purely ground-glass opacity.

Central tumours The cardinal imaging signs of a central tumour are collapse/ consolidation of the lung beyond the tumour and the presence of hilar enlargement, signs that may be seen in isolation or in conjunction with one another. Collapse/consolidation in association with central tumours Obstruction of a major bronchus often leads to a combination of atelectasis and retention of secretions with consequent

CHAPTER 18

Figure 18.2 CT demonstrating a second primary bronchogenic carcinoma in the right lung in a patient who had undergone a previous left pneumonectomy 7 years earlier. The new tumour has spiculated edges infiltrating into the adjacent lung (corona radiata).



PULMONARY NEOPLASMS

pulmonary opacity18, but collateral air drift may partially or completely prevent these postobstructive changes. Secondary infection may occur beyond the obstruction. The following features suggest that pneumonia is secondary to an obstructing neoplasm: 1 The shape of the collapsed or consolidated lobe may be altered because of the bulk of the underlying tumour. In cases with lobar collapse due to a central tumour mass, the fissure in the region of the mass is unable to move in the usual manner and, therefore, the fissure may show a bulge (the Golden S sign) (Fig. 18.8). 2 The presence of pneumonia in an at-risk patient, confined to one lobe (or more lobes if there is a common bronchus supplying these lobes) that persists unchanged for longer than 2–3 weeks, or a pneumonia that recurs in the same lobe, particularly if the lobe shows loss of volume and no air bronchograms. Simple pneumonia often clears or spreads to other segments within a few weeks. In practice,

Figure 18.3 (A) Squamous cell carcinoma resembling pneumonia. The entire opacity seen on this radiograph is due to the carcinoma itself. (B) Apical bronchiolo-alveolar cell carcinoma of the left upper lobe with ground-glass attenuation margins.

Figure 18.4 Examples of neoplastic cavitation on chest radiography. (A) The cavity is eccentric (large cell undifferentiated carcinoma). (B) The inner wall of the cavity is irregular and an air–fluid level is present (squamous cell carcinoma). (C) The cavity wall is very thin (squamous cell carcinoma).

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Figure 18.5 CT showing cavitating squamous cell carcinoma. The wall of the cavity is variable in thickness.

complete resolution of pneumonia virtually excludes an obstructing neoplasm as a cause of infection. Although consolidation may improve partially on appropriate antibiotic therapy, it almost never resolves completely if secondary to an underlying carcinoma. Occasionally, the opacified lobe will appear larger than normal because of the build-up of infected secretions beyond the obstructing carcinoma, an appearance that has been labeled the ‘drowned lobe’. 3 The presence of a visible mass or irregular stenosis in a mainstem or lobar bronchus. Careful analysis of CT images will demonstrate the presence of an obstructing tumour in virtually every case of postobstructive atelectasis due to a lung carcinoma19. 4 Simple pneumonia rarely causes radiographically visible hilar adenopathy, though enlarged central nodes may be seen on

Figure 18.6 Calcified infectious granuloma engulfed by lung cancer. CT shows a cluster of densely calcified small nodules almost at the centre of a small carcinoma.

Figure 18.7 Tumour calcification. Large bronchial carcinoma in left lower lobe showing extensive amorphous and cloud-like calcification. Initial examination; no treatment had been given.

CT or MRI. Lung abscess can occasionally be confused with bronchial carcinoma because it may result in hilar or mediastinal adenopathy20. 5 Mucus-filled dilated bronchi may be visible within collapsed lobes on a CT examination as branching, tubular low-density structures, and when seen should prompt a search for a centrally obstructing tumour (Fig. 18.9). Hilar enlargement is a common presenting feature in patients with bronchial carcinoma. It may reflect a proximal tumour, lymphadenopathy, consolidated lung, or a combination of these phenomena21–24. In general, the more lobular the shape, the more likely that metastatic lymphadenopathy is present. A mass superimposed on the hilum may lead to increased density of the hilum owing to summation of the opacity of the mass and that of the normal hilar shadows (Fig. 18.10).This sign may be the only indication of lung cancer on a frontal chest radiograph; when suspected, it is essential to inspect a lateral radiograph with care. Radiographic patterns based on cell type The radiographic pattern of bronchial carcinoma varies to a degree with the cell type, which may aid in the differential diagnosis prior to obtaining histological confirmation25. Early, often massive, hilar or mediastinal lymphadenopathy (Fig. 18.11) and direct mediastinal invasion are well-recognized phenomena in both small cell carcinoma and large cell carcinoma. Adenocarcinoma frequently shows hilar and mediastinal adenopathy26, though the nodal enlargement is not as massive as it is with small cell and large cell undifferentiated tumours. A mass in, or adjacent to, the hilum is a particular characteristic of small cell carcinoma, seen in 78% of cases. A peripheral nodule is very common in adenocarcinoma (72% of cases) and large cell tumours (63% of cases); it occurs approximately twice as often as with squamous or small cell carcinomas. The largest peripheral masses are seen with squamous and large cell tumours, whereas most adenocarcinomas and small cell carcinomas are less than 4 cm in diameter.

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PULMONARY NEOPLASMS

Figure 18.8 Lobe collapse. (A) Collapse of a lobe around a central mass. (B) The middle lobe has undergone collapse, but there is a central mass causing the central portion of both the oblique and horizontal fissures to bulge outwards (arrows).

Squamous cell cancers may attain great size and they cavitate more frequently than the other cell types; in one series cavitation was seen in 12% of squamous cell carcinomas presenting as a peripheral mass, compared with only 4–6% of peripheral large cell and peripheral adenocarcinomas27. Collapse/consolidation of the lung beyond the tumour is the most frequent feature seen with squamous cell carcinoma, in keeping with the predominantly central origin of this form of neoplasm. Pleural effusion (with dyspnoea) is a feature of adenocarcinoma.

Figure 18.9 Fluid-filled dilated bronchi beyond a central obstructing carcinoma are visible in this collapsed and consolidated left lower lobe.

Bronchiolo-alveolar carcinomas arise from the alveoli and the immediately adjacent small airways. They therefore present as peripheral pulmonary opacities rather than with the effects of large airway obstruction. The most common radiographic finding28 is a solitary lobulated or spiculated pulmonary mass indistinguishable from other types of carcinoma. Bubble-like lucencies corresponding to patent small bronchi, air-containing cystic lucencies, or air bronchograms and cavitation may be seen29,30. Bronchiolo-alveolar carcinomas

Figure 18.10 Dense hilum. The right hilum is dense owing to a mass superimposed directly over it. The mass proved to be a squamous cell carcinoma.

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Figure 18.11 Massive mediastinal adenopathy in a patient with small (oat) cell carcinoma of the bronchus. The primary carcinoma is not visible because it lies centrally in the bronchial tree.

may also appear as an ill-defined opacity resembling a patch of pneumonia; homogeneous consolidation of one lobe (which may be expansile); patchy consolidation; atelectasis; or multiple ill-defined nodules spread widely through multiple lobes in one or both lungs (Figs 18.12–18.14). Less commonly, a lepidic (scale-like) growth pattern or focal ground-glass opacity is seen31.

Figure 18.13 Bronchiolo-alveolar carcinoma. (A) Bronchiolo-alveolar carcinoma with widespread lung involvement. The appearance closely resembles bronchopneumonia or pulmonary oedema. (B) CT of a similar case showing the typical airspace filling with an obvious air bronchogram.

Staging intrathoracic spread of tumour

Figure 18.12 Bronchiolo-alveolar carcinoma occupying the right lower lobe. The appearance is identical to consolidation with partial collapse. Air bronchograms are present.

Lung cancer staging provides information about the anatomical extent and histological nature of disease, which allows the most appropriate treatment to be planned and gives an indication of prognosis. In those in whom surgery is not deemed appropriate, assessment of disease burden aids the oncologist to plan radiotherapy and chemotherapeutic regimens, and assists in the assessment of response to therapy. Small cell lung cancer is usually disseminated at the time of diagnosis. It is almost always treated medically, with the role

CHAPTER 18



PULMONARY NEOPLASMS

Figure 18.14 Bronchiolo-alveolar carcinoma. (A) Bronchiolo-alveolar carcinoma demonstrating lepidote growth in the left upper lobe. CT obtained during fine needle aspiration biopsy. (B,C) Biopsy-proven bronchiolo-alveolar cell carcinoma presenting as diffuse consolidation and ground-glass shadowing on chest radiography (B) and CT (C).

of imaging largely being to determine the extent of intrathoracic (limited versus extensive) and extrathoracic disease for the purposes of treatment planning. The International Staging System for Lung Cancer7 uses the TNM system to describe the findings (Table 18.1), and the stage is derived from the TNM description (Table 18.2) (T

signifies the primary tumour, N the regional lymph nodes and M distant metastases.) The system is used for non-small cell lung cancers. In essence: • Following the 1997 revision of the International Staging System for Lung Cancer7 Stage I has been divided into IA and IB based on demonstrable survival differences between

Table 18.1 TNM DEFINITIONS FOR THE INTERNATIONAL STAGING SYSTEM FOR LUNG CANCER7 Primary tumour (T) TX

Tumour proved by the presence of malignant cells in bronchopulmonary secretions but not visualized radiographically or bronchoscopically, or any tumour that cannot be assessed as in a retreatment staging

T0

No evidence of primary tumour

T1S

Carcinoma in situ

T1

A tumour that is 3 cm or less in its greatest dimension, surrounded by lung or visceral pleura and without evidence of invasion proximal to a lobar bronchus at bronchoscopy* (i.e. not in the main bronchus)

T2

A tumour more than 3 cm in its greatest dimension, or a tumour of any size that either invades the visceral pleura or has associated atelectasis or obstructive pneumonitis extending to the hilar region. At bronchoscopy the proximal extent of demonstrable tumour must be within a lobar bronchus or at least 2 cm distal to the carina. Any associated atelectasis or obstructive pneumonitis must involve less than an entire lung

T3

A tumour of any size with direct extension into the chest wall (including superior sulcus tumours), diaphragm, or the mediastinal pleura or pericardium without involving the heart, great vessels, trachea, oesophagus, or vertebral body; or a tumour in the main bronchus within 2 cm of the carina without involving the carina

T4

A tumour of any size with invasion of the mediastinum or involving the heart, great vessels, trachea, oesophagus, vertebral body, or carina, or presence of malignant pleural effusion**, or with satellite tumour nodule(s) within the ipsilateral primary tumour lobe of the lung

Nodal involvement (N) NX

Regional lymph nodes cannot be assessed

N0

No demonstrable metastasis to regional lymph nodes

N1

Metastasis to lymph nodes in the peribronchial or the ipsilateral hilar region, or both, including direct extension

N2

Metastasis to ipsilateral mediastinal lymph nodes and subcarinal lymph nodes

N3

Metastasis to contralateral mediastinal lymph nodes, contralateral hilar lymph nodes, ipsilateral or contralateral scalene, or supraclavicular lymph nodes

Distant metastasis (M) MX

Presence of distant metastases cannot be assessed

M0

No (known) distant metastasis

M1

Distant metastasis present—specify sites

*The uncommon superficial tumour of any size with its invasive component limited to the bronchial wall, which may extend proximal to the main bronchus, is also classified T1. **Most pleural effusions associated with lung cancer are due to tumour. However, there are a few patients in whom multiple cytopathological examinations of the fluid reveal no tumour. In these cases the fluid is non-bloody and is not an exudate. When these elements and clinical judgement dictate that the effusion is not related to the tumour, the effusion should be excluded as a staging element and the patient’s disease should be staged T1, T2, or T3. Pericardial effusion is classified according to the same rules.

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Table 18.2

• THE CHEST AND CARDIOVASCULAR SYSTEM

STAGING GROUPING. TNM SUBSETS7

Stage

TNM subset

0

Carcinoma in situ

IA

T1N0M0

IB

T2N0M0

IIA

T1N1M0

IIB

T2N1M0

of collapsed lung relative to tumour on contrast-enhanced CT may assist; collapsed lung tends to enhance to a greater extent than the adjacent tumour32, although this is not always the case32–34.T1 and T2 tumours are the most amenable to surgical resection using standard techniques. T3 tumours that involve the chest wall or mediastinum to a limited extent may also be candidates for surgical resection, albeit with more complex techniques. T4 tumours are irresectable.

T3N0M0 IIIA

T3N1M0 T1N2M0 T2N2M0 T3N2M0

IIIB

T4N0M0 T4N1M0 T4N2M0 T1N3M0 T2N3M0 T3N3M0 T4N3M0

IV

Any T Any N M1

*Staging is not relevant for occult carcinoma, designated TXM0N0. For each stage, the prognoses, or estimated 5-year survival rates, in Europe are as follows:

• Stage IA—60% • Stage IB—38% • Stage IIA—34% • Stage IIB—24% • Stage IIIA—13% • Stage IIIB—5% (Stage IIIB and IV lesions are non-resectable.) • Stage IV—< 1%

patients with T1N0M0 lesions at presentation compared with T2N0M0 lesions. Both these lesions are resectable with a reasonable hope of cure. • For similar reasons, Stage II has also been subdivided into IIA and IIB. These lesions are the same T lesions as stage I but with hilar node involvement or resectable mediastinal/ chest wall invasion. They are resectable for potential cure but with less good prognosis than stage I lesions. • Stage III is divided into IIIA, in which there is locally extensive intrathoracic disease and/or hilar and ipsilateral lymph node involvement which may be surgically resectable, and IIIB where the intrathoracic disease is beyond the limits of conventional surgical resection. IIIB tumours may be considered localized in terms of planning radiotherapy. • Stage IV includes all patients with distant metastatic disease. Staging the primary tumour CT is the most commonly used tool in evaluation of the primary tumour. Defining the primary tumour in terms of T staging enables prediction of resectability.Tumour size, location, margins and relationship to adjacent structures should be described. Assessment of tumour size may not be straightforward as distinction from adjacent collapsed lung may be impossible. Differential enhancement

Mediastinal invasion Plain radiograph evidence of mediastinal invasion relies on demonstrating phrenic nerve paralysis. Caution is needed, however, before deciding that a high hemidiaphragm is caused by phrenic nerve invasion, because lobar collapse can also lead to elevation of a hemidiaphragm, a subpulmonary effusion may mimic it, and diaphragmatic eventration is common. The major CT and MRI signs of mediastinal invasion include the demonstration of visible tumour deep within the mediastinal fat, particularly if tumour surrounds the mediastinal vessels, oesophagus, or proximal mainstem bronchi (Figs 18.15, 18.16). Associated pneumonia or atelectasis may make it very difficult to determine whether or not mediastinal contact is present. Even clear-cut contact with the mediastinum is not enough for the diagnosis of invasion, and the apparent interdigitation of tumour with mediastinal fat can be a misleading sign on both CT and MRI. Glazer et al35 showed that the presence of (A) less than 3 cm of contact with the mediastinum; (B) less than 90 degrees of circumferential contact with the aorta; or (C) a visible mediastinal fat plane between the mass and any vital mediastinal structures indicated a very high likelihood of technical resectability, even if the tumour had crossed into the mediastinum, and that most tumours in their series conforming to this description had no mediastinal invasion at surgery. When the question is turned round to enquire as to the criteria for irresectability, however, the answer is less certain36–39. Tumours that obliterate fat planes or show greater contact than that described above are not necessarily irresectable, though the greater the degree of invasion and the extent of contact, the more likely it is that there is significant mediastinal involvement37. MRI does not appear to offer any advantages over CT for the routine diagnosis of mediastinal invasion, its role being limited to problem solving in specific cases (Fig. 18.16)8. Before the advent of multidetector CT (MDCT), the multiplanar capabilities of MRI (Fig.18.17) could be used to advantage to identify involvement of major mediastinal blood vessels8,40 and the tracheal carina. MDCT has largely obviated the need to proceed to MRI to take advantage of multiplanar imaging alone; however, MRI sequences optimized for evaluation of the heart and vessels may still offer advantages where there is concern about invasion of hilar or mediastinal vessels41, the heart or pericardium. Chest wall invasion The presence of chest wall invasion alone does not preclude surgical resection, though it does adversely affect prognosis42,43. The necessarily more extensive surgery is associated with increased morbidity and mortality and it therefore helps the surgeon to know the extent of any chest wall invasion pre-operatively.

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Figure 18.15



PULMONARY NEOPLASMS

(A) Extensive deep mediastinal invasion by primary bronchial carcinoma. (B) On lung windows there are pulmonary metastases.

Figure 18.16 MRI of involved mediastinal nodes in a patient with a right lower lobe non-small cell lung cancer.

Figure 18.17 MRI of a left lower lobe tumour that has directly invaded the aortic wall which has altered signal adjacent to the tumour.

The diagnosis of chest wall involvement adjacent to a tumour is unreliable on CT, unless there is clear-cut bone destruction or a large soft tissue mass38–40,42–45 (Fig. 18.18). Local chest wall pain remains the single most specific indicator of whether or not the tumour has spread to the parietal pleura or chest wall44. Contact with the pleura on CT examination, even if the pleura is thickened (see Fig. 18.21), does not necessarily indicate invasion, though the greater the degree of contact and the greater the pleural thickening, the more likely it is that the parietal pleura has been invaded, particularly if the extrapleural fat plane is obliterated45. A definite extrapleural mass that is not explicable by previous chest trauma is likely to be the result of invasion by tumour45, but even this sign may be misleading since soft tissue swelling may be due to inflammation and fibrosis rather than neoplasm46. Conversely, a clear extrapleural fat plane adjacent to the mass may be helpful, but again not definitive, in excluding chest wall invasion47 (Fig. 18.19). In selected cases MRI has proved to be better than CT in demonstrating chest wall48,49 and diaphragmatic invasion. MRI is regarded as the optimal modality for demonstrating the extent of superior sulcus tumours (Pancoast’s tumour) (Fig. 18.18), reliably diagnosing mediastinal invasion, extension into the root of the neck and involvement of vascular and neural structures. Transthoracic ultrasound can identify chest wall invasion with a high degree of accuracy; however, the technique is rarely used for this purpose in Europe or the USA50. 99m Tc radionuclide skeletal scintigraphy is a sensitive technique with which to assess bone invasion and it may be positive when the plain radiograph still shows no bony abnormality. Intrathoracic lymph node metastases The American Thoracic Society’s description of nodal stations is the most widely used system to define the anatomical position of lymph nodes. Lung cancers normally spread to ipsilateral hilar nodes, then

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Figure 18.18 Chest wall invasion by a Pancoast’s tumour. Involvement of the soft tissues of the chest wall is appreciated on the (A) coronal T1- and (B) T2-weighted MRI images. (C) This example from a different patient shows the better demonstration of bone involvement (arrows) on CT.

ipsilateral mediastinal, contralateral mediastinal and supraclavicular nodes. Though nodal spread is most often sequential, skip metastases to mediastinal nodes in the absence of hilar nodes is seen in 33% of cases51. Generally chest radiography is insensitive for nodal staging. However, the presence of enlarged hilar or paratracheal nodes has been shown to be specific (92%) for N2–N3 disease8. Lymph node assessment on CT and MRI is limited to size, shape and location, with size being the major criterion used to predict metastatic involvement (Fig. 18.20). Normal mediastinal lymph node size on CT or MRI varies according to the location of the nodes within the mediastinum, but a simple and reasonably accurate rule is that nodes with a short axis diameter of less than 10 mm fall within the 95th percentile and nodes above this size should, therefore, be considered enlarged. The problem with using size as the only criterion for malignant involvement is that intrathoracic lymph node enlargement

has many nonmalignant causes, including previous tuberculosis, histoplasmosis, pneumoconiosis, sarcoidosis and, most importantly, reactive hyperplasia to the tumour (Fig. 18.21) or associated pneumonia/atelectasis: it has repeatedly been shown that one-half to two-thirds of enlarged nodes draining postobstructive pneumonia/atelectasis are free of tumour52. Conversely, microscopic involvement by tumour can be present in normal sized nodes. It will, therefore, be clear that there is no measurement above which all nodes can be assumed to be malignant and below which all can be considered to be benign. The sensitivity and specificity of CT for diagnosing metastatic involvement of mediastinal lymph nodes varies greatly in different published series, reflecting different size criteria and the methods used to confirm or exclude lymph node metastases. A reasonable generalization in the USA (where fungal infection is endemic) is that both sensitivity and specificity are in the 50 to low 60% range when the cut-off point for normal is a short axis diameter of 1 cm8,53,54. Better specificity figures

Figure 18.19 Cavitating bronchogenic carcinoma. There is preservation of the extrapleural fat plane at the point of contact with the chest wall. Although the pleura may be involved the chest wall is likely to be otherwise spared.

Figure 18.20 True-positive CT for metastatic lymphadenopathy. There are several enlarged nodes in the right paratracheal area. The largest measured 16 mm in its short axis diameter (arrow). The primary tumour was a bronchial carcinoma in the right lung.

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Figure 18.21 False-positive CT for metastatic mediastinal lymphadenopathy. The largest of the right paratracheal nodes (arrow) is 17 mm in its short axis diameter. This node proved to be free of malignant tumour at thoracotomy. The enlargement was due to reactive hyperplasia. None of the hilar or mediastinal nodes in this patient was involved by tumour. The primary tumour can be seen in the right lung. It shows extensive contact with the right chest wall, but no definite evidence of invasion of the chest wall on CT. At surgery there was invasion of the soft tissues of the chest wall but no spread to the ribs.

have been obtained in Europe55 and Japan56, probably because the prevalence of coincidental histoplasmosis is much lower than in the USA.The positive predictive value for nodal metastatic disease may be improved (to up to 95%) by ensuring that nodes draining the tumour are larger than nodes elsewhere in the mediastinum55. The accuracy of MRI, despite its improved contrast resolution, is limited by the same constraint as for CT of overlap of features of benign and malignant causes of node enlargement. Although it is generally considered that the MRI signal within nodes is not a useful predictor of involvement, a recent study has reported that STIR imaging produces sufficient signal



PULMONARY NEOPLASMS

difference between normal and pathological nodal tissue to detect metastases with 93% sensitivity and 87% specificity57. The previously cited advantage of MRI over CT in nodal detection due to its ability to distinguish small nodes from vessels without intravenous enhancement has been effectively negated by the advantages of MDCT. Endoscopic ultrasound (EUS) can be used to assess the size and morphology of, and to guide fine needle aspiration (FNA) of, aortopulmonary, subcarinal and posterior mediastinal nodes58, achieving greater sensitivity and specificities for nodal involvement than CT and PET in some series59. Ultrasound assessment (± FNA) of supraclavicular lymph nodes improves sensitivity for detection of supraclavicular lymph node involvement; its routine use has been suggested as a method to improve the accuracy of pre-operative staging60. PET imaging with fluorodeoxyglucose (FDG) is increasingly used for staging lung carcinoma, with published studies consistently demonstrating greater accuracy compared to CT and MRI in the detection of nodal disease (Fig. 18.22). Falsepositive results still occur, most commonly due to inflammation and reactive hyperplasia. In one meta-analysis of nodal staging the sensitivity of PET was 79% and specificity was 91%, compared with 60% and 70% respectively for CT61. Fused PET–CT imaging provides registration of FDG metabolic activity with the anatomical detail of CT (Fig. 18.22); it has been reported to be more accurate than PET or CT alone in staging patients with non-small cell lung cancer62–64. Decision analysis studies have shown that PET can be incorporated into the work-up of lung cancer in a cost-effective manner, with savings derived from identifying inoperable patients before thoracotomy65,66. Mediastinoscopy and mediastinotomy remain the most widely employed techniques for mediastinal lymph node sampling. They have high sensitivity and specificity for detecting malignant disease and, although invasive, are indicated prior to thoracotomy when other forms of imaging suggest nodal involvement.

Figure 18.22 Recurrent malignant right hilar lymph nodes from a small peripheral non-small cell lung cancer. (A) CT demonstrates nodes at the right hilum. (B) The PET–CT image confirms high FDG uptake in keeping with malignant involvement.

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Pleural involvement may occur as a result of direct spread, lymphatic involvement, or tumour emboli. On occasion, adenocarcinoma takes the form of a sheet of lobular pleural thickening indistinguishable from malignant mesothelioma. A pleural effusion in association with a primary lung cancer designates the tumour as being T4. The exception is the few patients who have clinical evidence of another cause for the effusion (e.g. heart failure) and in whom cytology examinations of multiple pleural fluid samples are negative for tumour cells, in which case the effusion can be disregarded as a staging criterion. Attempts to characterize the nature of the pleural fluid based on density measurements at CT or signal intensities at MRI have not so far proved useful. Several studies suggest PET may have a role in the evaluation of pleural effusion in patients with lung cancer, although this requires further evaluation67–69. Summary Staging the intrathoracic extent of lung cancer is a multidisciplinary process utilizing imaging, bronchoscopy and biopsy. Chest radiography, CT and PET (where available) are currently the routine imaging procedures for assessing intrathoracic spread and determining resectability, with MRI and ultrasound reserved for specific indications. The essential points to establish when staging the intrathoracic extent of non-small cell cancers are: (A) whether or not the tumour has spread to hilar or mediastinal nodes; (B) if it has, which nodal groups are involved; (C) whether or not the tumour has invaded the chest wall or mediastinum; and (D) if it has, whether it is still potentially curable surgically. If chest radiography and CT ± PET show no evidence of spread beyond the lung (other than to ipsilateral hilar nodes) in a patient who is suitable for surgery, and in whom bronchoscopy shows the tumour to be resectable, then that patient should be offered surgical resection without further pre-operative invasive procedures. Spread to ipsilateral nodes, whilst not necessarily precluding surgical resection, has a significantly adverse effect on prognosis and if surgery is undertaken, it is performed with the understanding that 5-year survival rates are poor. The poor specificity of CT in determining nodal involvement must be appreciated. Nodal enlargement, whilst probably due to metastatic carcinoma, may also be due to coincidental benign disease, reactive hyperplasia to the presence of the tumour, or to any associated obstructive consolidation/atelectasis. Thus biopsy confirmation of neoplastic nodal involvement by mediastinoscopy, mediastinotomy, or needle aspiration is usually essential before a patient is denied surgery. Positive PET findings for nodal involvement do not obviate the need for histological confirmation of nodal involvement. However, in patients with no enlarged lymph nodes on CT and normal findings on PET, the likelihood of nodal involvement is so low that mediastinoscopy can be omitted. For lung cancers that have invaded the mediastinum or chest wall, it is important to decide whether the tumour is nevertheless resectable for possible cure, again recognizing that the prognosis will be poorer than for tumours confined to the lung. CT may show definitively that the tumour is too

extensive for resective surgery (i.e. that it is a T4 lesion)54. Alternatively CT may leave the issue in doubt and MRI may then help to solve the problem.

Extrathoracic staging of lung cancer Lung cancer is commonly associated with widespread haematogenous dissemination at the time of presentation. Sites of spread include the adrenal glands, bones, brain, liver and more distant lymph nodes. Detection of metastatic disease precludes surgical resection of the primary tumour. There is evidence to support the approach of extending the staging chest CT to include the liver and adrenals, with no further imaging being undertaken in the absence of clinical features suggesting metastatic disease. Currently, there is a lack of consensus regarding whether or not to perform more extensive extrathoracic screening in patients who otherwise have potentially operable disease. The increased availability of PET and PET–CT, with its greater sensitivity for detecting occult extrathoracic metastatic disease, may well result in a change in practice to include routine assessment for extrathoracic disease. In patients initially selected for curative resection using standard tumour staging, PET–CT has been reported to detect occult metastatic disease in 11–14% of patients, and to alter management in up to 40%61,70,71. A more detailed discussion of this topic is beyond the scope of this chapter.

Missed lung cancer Whether the failure to diagnose a lung cancer on an initial chest radiograph, seen only in retrospect, constitutes malpractice or whether such ‘misses’ are inevitable can be a difficult decision72,73. Forty-five of the 50 potentially visible primary peripheral lesions in one part of the National Cancer Institutes (NCI) screening programme had been overlooked on at least one previous chest radiograph, though it should be realized that the opacities in question were often very subtle74. Similarly, Heelan et al found that 65% of cancers had been overlooked in a yearly screening programme75. Lung cancers may also be overlooked at CT; the majority of missed cancers on CT are endobronchial or perihilar in location. If failure to diagnose a lung cancer at the first opportunity, however subtle the abnormality, were automatically to be regarded as malpractice, then radiologists would be found guilty of malpractice even though their radiographic reporting conformed to the same standards as those of a group of experienced chest radiologists. Clearly the dividing line between negligence and acceptable practice is difficult to define72. It is worth noting, however, that a legal case will sometimes hinge on the technical adequacy of the radiographs and appropriate communication of the findings, as well as on the issue of interpretation.

PULMONARY SARCOMA AND OTHER PRIMARY MALIGNANT NEOPLASMS The majority of pulmonary sarcomas in the lungs are metastases from extrathoracic primary tumours. Primary pulmonary sarcomas are rare, the most common primary forms

CHAPTER 18

being fibrosarcoma and leiomyosarcoma. Chondrosarcoma, fibroleiomyosarcoma, rhabdomyosarcoma, malignant fibrous histiocytoma, carcinosarcoma, liposarcoma and osteosarcoma are among the other sarcomas that may occasionally arise as primary airway or pulmonary tumours. All the above neoplasms present as a solitary pulmonary nodule or as a tracheal or endobronchial mass indistinguishable radiologically from bronchial carcinoma. Angiosarcomas of the pulmonary artery extend or arise intravascularly. The autoimmune deficiency syndrome (AIDS) epidemic has led to an increased number of cases of Kaposi’s sarcoma involving the lung. Kaposi’s sarcoma in the respiratory tract appears to be rare in the absence of cutaneous involvement76,77. Coincidental involvement of the tracheobronchial tree is relatively frequent but parenchymal involvement may occur in the absence of endobronchial disease. Imaging may show the disease to be focal or widespread78–80. Focal segmental or lobar opacities are usually due to the tumour itself, but endobronchial Kaposi’s sarcoma may result in atelectasis or postobstructive pneumonia81. Radiographically widespread disease is the more frequent pattern, with a tendency to perihilar predominance of linear, rounded, or reticulonodular shadowing, reflecting a bronchocentric distribution of the lesions79 (Fig. 18.23). The pulmonary opacities of Kaposi’s sarcoma do not fluctuate in severity, whereas the major differential diagnoses—pulmonary oedema and opportunistic infections—may do so. Intrathoracic hilar/mediastinal lymphadenopathy has been detected in 25–60% of cases in some series78,79,82. Pleural involvement is frequent78,83; pleural effusions are most commonly bilateral and may on occasion be large.



PULMONARY NEOPLASMS

Other rare malignant pulmonary neoplasms include haemangiopericytoma, pulmonary blastoma, plasmacytoma, choriocarcinoma, teratoma and Askin tumours. The most common malignant tumour of the trachea is invasion from an adjacent neoplasm, notably bronchial carcinoma. Primary malignant tracheal tumours are rare and are virtually confined to adults.The least infrequent is squamous cell carcinoma, followed by adenoid cystic carcinoma and mucoepidermoid carcinoma84,85 (Fig. 18.24). These three tumours make up over 90% of primary malignant tracheal tumours, the remaining 10% encompassing a wide variety of neoplasms, including sarcoma, lymphoma, adenocarcinoma, chondrosarcoma, plasmacytoma, small cell carcinoma and metastases. Some malignant tracheal tumours may present on imaging studies as a mural nodule with lobular or irregular contours, whereas some grow circumferentially as a stenosing lesion of variable length. All these tumours grow through the tracheal wall to produce a paratracheal mass, a feature most frequently seen with adenoid cystic carcinoma. Like bronchial carcinoid and various benign tumours, adenoid cystic carcinomas may calcify.

BENIGN PULMONARY TUMOURS Bronchial carcinoids Bronchial carcinoids are uncommon, constituting less than 5% of pulmonary tumours.The peak age at diagnosis is in the fifth decade, but the age range is wide and includes children. Two forms of bronchial carcinoid are described: typical (85– 90%) and atypical (10–15%).Typical carcinoids most commonly arise in central airways. Atypical carcinoids usually arise in the

Figure 18.23 Kaposi’s sarcoma in two patients with AIDS. (A) Plain chest radiograph showing extensive pulmonary shadowing consisting of a mixture of ill-defined rounded and bandlike shadows maximal in the perihilar regions and lower zones. (B) CT showing the peribronchial distribution of the illdefined pulmonary nodules. There is interlobular septal thickening, a feature that is also frequently identified on the chest radiograph.

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Pulmonary hamartoma

Figure 18.24 Adenoid cystic carcinoma of the trachea. There is irregular polypoid tumour within the tracheal lumen.

lung periphery. Despite their classification as benign neoplasms, bronchial carcinoids can invade locally and may metastasize to hilar and mediastinal lymph nodes as well as to the brain, liver and bone. The atypical carcinoids have histological and clinical features intermediate between typical bronchial carcinoid and small cell carcinoma of the lung86, and have a poorer prognosis. Bronchial carcinoid may present with wheeze, pneumonia, or haemoptysis. Even when small, tumours may secrete adrenocorticotropic hormone (ACTH) in sufficient quantities to cause Cushing’s syndrome. Carcinoid syndrome is very rare if the tumour is still confined to the lung. Radiographic appearances vary with location of the tumour87–89. There is no lobar predilection and on rare occasions carcinoids may arise in the trachea. Bronchial carcinoids, particularly those located centrally, may calcify and occasionally ossify. Calcification is seen on CT in up to one-third of cases, but is only occasionally visible on chest radiograph90. Marked contrast enhancement may be seen on CT. Carcinoids arising in central bronchi (80–90% of cases) often show a larger mass external to the bronchus than within the lumen (‘iceberg’ lesions), and the extrabronchial component may be visible as a hilar mass (Fig. 18.25). Central lesions usually produce partial or complete bronchial obstruction, resulting in atelectasis with or without pneumonia. Central bronchial obstruction may be complicated by development of distal bronchiectasis or lung abscess. Occasionally, a bronchial carcinoid in a segmental or subsegmental bronchus may obstruct bronchial secretions, thereby causing a mucocele. Peripheral lesions (10–20% of carcinoids) present as solitary spherical or lobular nodules, 2–4 cm in diameter, with a welldefined smooth edge. Noncalcified peripheral bronchial carcinoid tumours closely resemble bronchial carcinomas, both radiologically and cytologically and are therefore frequently removed surgically in the belief that they are carcinomas.

Hamartomas are tumour-like malformations composed of an abnormal mixture of mature tissues normally found in the organ in which the tumour occurs. Pulmonary hamartomas consist predominantly of masses of cartilage with clefts lined by bronchial epithelium and may contain large collections of fat. Malignant transformation is either nonexistent or extremely rare. Pulmonary hamartomas are very occasionally multiple. A triad of pulmonary chondroma(s) (often multiple), gastric epithelioid leiomyosarcoma (leiomyoblastoma) and functioning extra-adrenal paragangliomas, known as Carney’s triad, has been reported, as has a form with just pulmonary chondromas and gastric smooth muscle tumours91,92. The age range for hamartoma is from young adulthood to old age, with presentation peaking in the seventh decade; they are only occasionally seen in children. The distribution of pulmonary hamartomas is opposite to that seen with bronchial carcinoid: 90% are peripheral and present as a solitary pulmonary nodule, while the remaining 10% arise within a major bronchus. Central lesions may lead to major airway obstruction and the features are then identical to those seen with bronchial carcinoids. On plain chest radiography93,94 the tumour is seen as a spherical or slightly lobulated, well-defined nodule, usually less than 4 cm in size, with normal surrounding lung (Fig. 18.26). Some hamartomas show calcification, which may be spotty or linear or show the characteristic ‘popcorn’ configuration associated with calcification in cartilage (Fig. 18.26). The frequency of calcification increases significantly with the size of the lesion. Popcorn calcification, if present, is virtually diagnostic of a hamartoma (the only differential diagnosis is a chondrosarcoma). Central fat density on CT is another important finding, which, if present, establishes the diagnosis95. The lesions grow slowly, usually much more slowly than carcinoma of the bronchus, and cavity formation is almost unknown.

Other benign pulmonary neoplasms Fibroma, chondroma, lipoma, haemangioma, benign clear cell tumours, neurogenic tumours, chemodectoma and granular cell myoblastoma are benign neoplasms that are occasionally encountered in the trachea, bronchi, or lungs. The plain radiograph and CT findings vary with the size and location of the tumour mass, but no features distinguish any one of these lesions from any other, and therefore the specific diagnosis has to be made histologically. They are indistinguishable radiologically from carcinoid tumour and solitary metastasis. Leiomyoma of the lung may be a solitary lesion, radiographically indistinguishable from the other benign connective tissue neoplasms. Multiple leiomyomas present as multiple discrete nodules in the lungs96. They are given a wide variety of names, including benign metastasizing leiomyoma. In women these tumours may be very slow growing metastases from a uterine leiomyoma; women with multiple pulmonary leiomyomas often have a history of previous hysterectomy for uterine fibroids.

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PULMONARY NEOPLASMS

Figure 18.25 Carcinoid tumour. (A) A small tumour is completely occluding the right main bronchus and causing extensive collapse in the right lung. The endoluminal component is well seen (arrows), but there is poor differentiation of the tumour from adjacent collapsed lung. (B) A well-defined perihilar carcinoid tumour (arrows) is demonstrated anterior to the artery to the right lower lobe. (C) On lung windows there is only a small band of atelectasis in the middle lobe. (D) A small peripheral carcinoid tumour indistinguishable from a number of other causes of a solitary pulmonary nodule.

Intrapulmonary teratomas are very unusual. Most are benign, though malignant lesions are occasionally encountered. Radiographically and on CT, intrapulmonary teratomas appear as lobulated masses that may show calcification or cavitation97.

to be viral in origin. Rarely, these papillomas are also present in the lung and are seen on plain chest radiography or CT as multiple, small, widely scattered and well-defined, round pulmonary nodules, frequently showing cavitation101,102.

Plasma cell granuloma of the lung (inflammatory pseudotumour) is the name given to a lesion that is presumed to be reactive inflammatory granulomatous tissue98. The age range is wide and includes children. Most patients present with an asymptomatic solitary pulmonary nodule. Cavitation and calcification have both been described.

Benign tumours of the trachea are rare. They are most frequent in children, in whom squamous papillomas are the most common type, the next most common being haemangiomas. Haemangiomas are often associated with cutaneous haemangiomas and frequently present in the first year of life with stridor; imaging examinations show them to be eccentrically located nodular masses, most often in the subglottic region.

Sclerosing haemangioma is a benign neoplasm99,100, which almost always presents as an asymptomatic solitary pulmonary mass. Calcification may be seen. Squamous papillomas of the trachea, bronchi and lungs are most commonly associated with laryngeal papillomatosis, a disease that usually commences in childhood and is believed

BENIGN LYMPHOPROLIFERATIVE DISORDERS Lymphocytic interstitial pneumonia Lymphocytic interstitial pneumonia (LIP) is an uncommon non-neoplastic lymphoproliferative disorder characterized by

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Figure 18.26 Hamartoma of the lung. (A,B) Round, completely smooth, hamartoma in a 57 year old asymptomatic man. There is typical coarse popcorn calcification in this lesion which is unusually large.

diffuse infiltration of the pulmonary parenchymal interstitium by lymphocytes and plasma cells98. Histological differentiation between benign proliferation and low grade lymphoma can be difficult. LIP may occur as an isolated entity (it is included in the classification of idiopathic interstitial pneumonias); however, this is rare. It is more commonly seen in association with an underlying immunological abnormality such as Sjögren’s syndrome and AIDS. The main imaging findings are of bilateral areas of ground-glass opacification and cysts103.

Follicular bronchiolitis Follicular bronchiolitis, also known as diffuse lymphoid hyperplasia, is characterized by hyperplasia of bronchial mucosa associated lymphoid tissue (MALT) in relation to airways. Reticular or reticular nodular shadowing with centrilobular nodules and ground-glass opacity and occasionally bronchial wall thickening, bronchial dilatation, interlobular septal thickening and peribronchovascular airspace consolidation, is seen104.

visible intrathoracic adenopathy, whereas in the non-Hodgkin’s lymphomas, isolated pulmonary involvement is not uncommon107. If the mediastinal and hilar nodes have been previously irradiated, then recurrence confined to the lungs may be seen in both Hodgkin’s and non-Hodgkin’s lymphoma. The radiographic appearances of lung involvement in malignant lymphoma vary108,109. The usual patterns are: (A) one or more areas of pulmonary consolidation resembling pneumonia (Fig. 18.27); (B) multiple pulmonary nodules (Fig. 18.28); and, occasionally (C) miliary nodulation or reticulonodular shadowing resembling lymphangitis carcinomatosa (Fig. 18.29). The areas of pulmonary consolidation, which may contain air bronchograms, may be segmental or lobar in shape, but often they radiate from the hila or mediastinum without conforming to segmental anatomy, in keeping with the concept that extension into the lungs is by direct invasion from involved hilar or mediastinal nodes. Peripheral subpleural masses or areas of consolidation without any visible connection to enlarged nodes in the mediastinum and hila are, however, common in both Hodgkin’s disease and non-Hodgkin’s lymphoma. Very rapid increase in the size of lymphomatous deposits in the lung, so rapid that the disease may be confused with pneumonia, has been reported with high grade non-Hodgkin’s lymphoma110. Primary lymphoma of the lung (see Fig 18.27) (i.e. lymphoma isolated to the lung at initial presentation) is very uncommon, non-Hodgkin’s lymphoma of MALT type being the most frequently encountered form. These are low grade B-cell lymphomas of MALT (also called bronchus associated lymphoid tissue or BALT), which consists of mucosal lymphoid follicles located in distal bronchi and bronchioles, particularly at airway bifurcations98. The second most common primary tumour, known as angiocentric immunoproliferative lesion or lymphoid granulomatosis, is high grade and may have B- or T-cell phenotype98. Primary pulmonary Hodgkin’s disease is notably rare.

MALIGNANT LYMPHOPROLIFERATIVE DISORDERS Lymphoma Only pulmonary parenchymal involvement by lymphoma is considered in this chapter. Pulmonary parenchymal involvement can be broadly divided into that occurring in association with existing or previously treated nodal disease, and that due to primary lymphoma of the lung (Hodgkin’s or non-Hodgkin’s). Parenchymal involvement is comparatively rare at initial presentation (10–15% of cases105), but it becomes considerably more common as the disease progresses. It is particularly frequent in patients who relapse after treatment106. Involvement of the lung appears to be three times as frequent in Hodgkin’s lymphoma as it is in non-Hodgkin’s lymphoma105. In Hodgkin’s lymphoma the lung disease is almost invariably accompanied by

Figure 18.27 Primary pulmonary lymphoma. This appearance had been very slowly progressive over several years.

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PULMONARY NEOPLASMS

be a striking feature. A few of the lesions show cavitation, but calcification does not occur. MALT lymphomas are relatively rarely associated with pleural effusions despite contact with the pleura.

Other findings in pulmonary lymphoma

Figure 18.28 Pulmonary involvement by lymphocytic lymphoma showing multiple pulmonary masses.

The imaging features of MALT111–113 lymphomas are solitary or multifocal, round or segmental areas of pulmonary consolidation. There is no lobar predilection and the consolidations may be placed centrally or peripherally in the lung parenchyma. Air bronchograms are frequently visible and may

Lobar atelectasis caused by endobronchial lymphoma is occasionally encountered, but, somewhat surprisingly, atelectasis as a result of extrinsic compression by enlarged lymph nodes is rare, with encasement rather than obstruction being the usual pattern of disease. Pleural effusions are common except in MALT lymphoma. They are usually unilateral and accompanied by visible intrathoracic adenopathy. They frequently disappear once the mediastinal nodes have been irradiated; in such cases they are probably due to venous or lymphatic obstruction rather than neoplastic involvement of the pleura. The usual radiographic problem is in deciding whether the pulmonary abnormality is due to involvement by lymphomatous tissue, infection or a complication of therapy. It should be remembered that the pattern of pulmonary infection in patients with lymphoma is modified because they are immunocompromised hosts, owing either to their disease or, more often, to the drugs used for treating the disorder. In many instances, a biopsy is the only way to establish the precise diagnosis. Since Hodgkin’s disease is believed to spread from nodal sites, a useful guideline is that if a patient presents with Hodgkin’s lymphoma and a pulmonary opacity, but no evidence of hilar or mediastinal disease, it is more likely that the opacity represents something other than Hodgkin’s lymphoma114. A caveat here is that the patient should not previously have received radiation therapy to the mediastinum.

Leukaemia

Figure 18.29 Pulmonary involvement by non-Hodgkin’s lymphoma showing an appearance closely resembling lymphangitis carcinomatosa with widespread nodules and thickened septal lines.

The incidence of leukaemic infiltration of the lungs, mediastinal lymph nodes and pleura varies with the course of the disease. Pulmonary infiltration by leukaemic cells is found at autopsy in nearly two-thirds of patients who have leukaemia. However, provided those patients with leukostasis (see below) are considered separately, leukaemic infiltration of the lungs, though very common pathologically, is usually asymptomatic and is rarely a cause of significant pulmonary opacity on chest radiograph. When respiratory impairment is present, pulmonary infection, oedema or haemorrhage, are more likely causes of the patient’s symptoms115. Imaging features include diffuse bilateral reticulation and patterns resembling interstitial oedema; lymphangitic carcinomatosis, small nodules, ground-glass opacification and consolidation have also been described.116 Radiographically visible hilar and/or mediastinal lymph node enlargement may be present and pleural effusions are common, though it is not possible to state the cause of the effusion with any confidence. The distribution of nodal enlargement closely resembles that of the lymphomas. T-cell leukaemias may show massive mediastinal adenopathy that responds rapidly to chemotherapy or radiation treatment. Huge mediastinal masses of T-cell leukaemia may disappear within a few days following appropriate treatment.

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Pleural thickening due to a mass of leukaemic cells in patients with myeloid leukaemia, so-called granulocytic sarcoma or chloroma formation (because of its green appearance), may be encountered on rare occasions117–119. Leukostasis is seen in patients with acute myeloid leukaemia with very high white blood cell counts in the order of 100 000–300 000 cells mm−3. The patients may be dyspnoeic because of the obliteration of their small pulmonary blood vessels by the leukaemic cells117. The chest radiograph may be normal or show airspace shadowing, which is probably due to pulmonary oedema rather than directly to the accumulation of leukaemic cells in the lungs120,121.

METASTASES Pulmonary metastases122 in adults are usually from breast, gastrointestinal tract, kidney, testes, head and neck tumours or from a variety of bone and soft tissue sarcomas. The basic sign of haematogenous pulmonary metastasis is one or more discrete pulmonary nodules (Fig. 18.30), usually in the outer portions of the lungs, a distribution that is most evident on CT (Fig. 18.31). The nodules are usually spherical and well defined, but they may be almost any shape and can occasionally have a very irregular edge. Such irregular edges are seen particularly with metastases from adenocarcinomas (Fig. 18.32). Cavitation is occasionally seen in pulmonary metastases; it is a particular feature of squamous cell carcinoma123. Calcification is very unusual except in osteosarcoma and chondrosarcoma. Even if the primary tumour shows calci-

Figure 18.30 Typical pulmonary metastases showing multiple, welldefined spherical nodules in the lungs. Rib metastases with associated soft tissue swelling are also present (arrows). In this case the primary tumour was a synovial cell carcinoma.

Figure 18.31 Pulmonary metastases (arrow). CT demonstrating a single peripheral metastasis (arrow). There were multiple lesions at other levels. The volume loss and scarring in the left lung is secondary to previous resection of the primary bronchogenic carcinoma.

fication, e.g. in breast and colon, visible calcification in the pulmonary metastases is rare.The rate of growth of metastases is highly variable; in some choriocarcinomas and osteosarcomas, for example, it may be explosive and double the volume of the lesions in less than 30 d124. Alternatively, metastases can remain unchanged in size for a long time, as in some cases of thyroid carcinoma125. A solitary pulmonary metastasis may be the presenting feature in a patient without a known primary tumour. However, a metastasis is a rare cause of the asymptomatic pulmonary

Figure 18.32 Irregular pulmonary metastases due to metastatic adenocarcinoma from an unknown primary. The nodules are irregular in outline. A large left pleural effusion is also present.

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nodule in patients who do not have a known extrathoracic primary neoplasm, comprising no more than 2–3% of most series. The simplest technique for diagnosing pulmonary metastases is the plain postero-anterior (PA) and lateral chest radiograph. High-kV techniques are often used routinely, since substantial portions of the lungs are obscured on low-kV radiographs by overlying structures such as the diaphragm, heart, mediastinum, hila and ribs. Such radiographs will detect most lung metastases above 1 cm in diameter. Increasing sensitivity can be obtained with CT, in particular MDCT. The increase in sensitivity for small nodules is, however, at the cost of decreasing specificity. On CT, lesions smaller than 1 cm are regularly demonstrated, together with most lesions above 3 mm in diameter. Below 1 cm and particularly below 6 mm, the differential diagnosis from granulomas due to tuberculosis, histoplasmosis, or other fungi becomes difficult. Where calcification can be identified, metastases (except from osteogenic sarcoma or chondrosarcoma) can effectively be dismissed from consideration. If the nodules are not calcified, the best that can be done in most instances is to give a statistical probability of the nodules being metastases. With a plain chest radiograph showing multiple noncalcified nodules, the probability is high, well over 90%, even in areas endemic for fungus granulomas, and approaches 100% in areas where fungus granulomas are rare or nonexistent. With the smaller lesions detectable on CT, this probability diminishes. Depending on the prevalence of infectious granulomas in the community and the likelihood of a particular tumour metastasizing to the lung, the probability that a pulmonary nodule seen solely on CT is indeed a metastasis may drop to as low as 50%. The use of chest CT to detect pulmonary metastases should be limited to selected patients. There are no universally agreed guidelines but general indications include: 1 Investigation of patients with a normal chest radiograph in whom the likelihood of metastasis is high and in whom demonstration of the presence of pulmonary metastases would significantly alter management, e.g. patients with osteosarcoma, choriocarcinoma and testicular germ-cell tumours. 2 Investigation of patients who are being considered for surgical resection of a known pulmonary metastasis to look for further occult lesions. 3 Distinction of solitary from multiple pulmonary nodules in a patient with an extrathoracic primary tumour in whom the diagnostic question is metastasis versus new primary bronchial carcinoma. A truly solitary pulmonary nodule may represent a primary bronchogenic carcinoma, whereas multiple nodules make metastases more likely. Currently CT is the most cost-effective and widely used method of screening for pulmonary metastases. PET can be useful for detection of thoracic metastases for tumours such as melanoma, colon and breast. The major weakness of PET alone is the limited sensitivity for nodules less than 10 mm in diameter.



PULMONARY NEOPLASMS

Lymphangitic carcinomatosis Lymphangitic carcinomatosis is the name given to permeation of pulmonary lymphatics and/or their adjacent interstitial tissue by neoplastic cells.The most common tumours that spread in this manner are carcinomas of the bronchus, breast, stomach and prostate126. Lymphangitic carcinomatosis may develop secondary to blood-borne emboli lodging in smaller pulmonary arteries and subsequently spreading through the vessel walls into the perivascular interstitium and lymphatic vessels. Such spread tends to give rise to bilateral symmetric pulmonary abnormality. Alternatively, lymphangitic carcinomatosis may result from direct extension of tumour from hilar lymph nodes into peribronchovascular interstitium, from the pleura into adjacent interlobular septa, or from a primary carcinoma of the lung into the adjacent peribronchovascular interstitium. Tumour spreading by these mechanisms tends to be more localized98. The radiological findings are fine reticulonodular shadowing and/or thickened septal lines (Figs 18.33, 18.34). These signs occur because of a combination of dilated lymphatics and interstitial oedema, together with shadows due to the tumour cells themselves along with any desmoplastic response which may have been induced by the tumour98,126. Another useful sign of lymphangitis carcinomatosa is subpleural oedema resulting from lymphatic obstruction by tumour cells, a feature that is most readily visible as thickening of the fissures. Pleural effusion is common, seen in about 30%. As would be expected, CT is more sensitive than plain radiography in the detection of lymphangitic spread and may show changes in patients whose chest radiograph is normal. CT, particularly high-resolution CT127–130, shows nonuniform, often nodular, thickening of the interlobular septa and irregular thickening of the bronchovascular bundles in the

Figure 18.33 Unilateral lymphangitic carcinomatosis due to carcinoma of the bronchus, showing thickened septal lines and nodules confined to the right lung.

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Figure 18.34 Bilateral lymphangitic carcinomatosis showing bilateral thickened septal lines together with widespread nodulation of the lungs. The primary tumour in this 71 year old woman was presumed to be a bronchial carcinoma (a diagnosis based on sputum cytology).

Figure 18.35 High-resolution CT of lymphangitic carcinomatosis. Note the variable thickening of the interlobular septa and the enlargement of the bronchovascular bundle in the centre of the secondary pulmonary lobules. The polygonal shape of the walls (septa) of the secondary pulmonary lobules is particularly well shown anteriorly. The pulmonary nodule is due to a discrete metastasis, a relatively frequent finding in this condition.

Tumour emboli central portions of the lungs (Fig. 18.35). Small, peripherally located, wedge-shaped densities are sometimes seen as well; these may represent volume averaging of the thickened septa. There is often patchy airspace shadowing, but an important differential diagnostic feature from pulmonary oedema is that many of the acini subtended by thickened interlobular septa are normally aerated. Nodular shadows may be seen scattered through the parenchyma. The abnormalities may involve all zones of both lungs or they may be centrally or peripherally predominant; sometimes, particularly when lymphangitis is due to bronchial carcinoma, they are confined to a lobe or one lung. Hilar lymph node enlargement is seen in only some of the patients.

Unusual patterns of metastatic cancer Endobronchial metastases Endobronchial metastases are most unusual. Melanoma and renal, colorectal and breast carcinomas are the primary tumours that most frequently give endobronchial submucosal metastases131. In such cases the effect of airway obstruction is the dominant feature.

Miliary metastases Occasionally, innumerable tiny nodules closely resembling miliary tuberculosis are seen throughout both lungs, with no large masses and no evidence of lymphatic obstruction, such as is seen in lymphangitis carcinomatosa. Metastases are, however, one of the rarest causes of this pattern. The primary tumours that are most likely to produce miliary nodulation of the lungs are thyroid and renal carcinomas, bone sarcomas and choriocarcinoma.

Radiologically recognizable pulmonary arterial hypertension may occur on rare occasions as a result of tumour emboli blocking small pulmonary arteries132. Many tumours can embolize in this fashion, particularly hepatoma, carcinoma of the breast, kidney, stomach, and prostate and choriocarcinoma132.

EVALUATION OF THE SOLITARY PULMONARY NODULE A solitary pulmonary mass or nodule is defined as a solitary circumscribed pulmonary opacity with no associated pulmonary, pleural, or mediastinal abnormality, measuring less than 3 cm in diameter133. Many are discovered incidentally at chest radiography or CT. Although most are benign, up to 40% of these nodules may be malignant, with the relative incidence varying amongst different patient populations, e.g. there is a relatively higher incidence of granulomas in countries where fungal disease is endemic. Table 18.3 lists some of the causes of the solitary nodule, and Table 18.4 some of the mimics. The primary role of radiological investigation is to differentiate benign from malignant disease. It is as important to avoid a false-positive diagnosis of cancer with an unnecessary operation as to avoid a false-negative diagnosis leaving a potentially resectable cancer untreated. Chest radiography and CT are the primary imaging investigations used, with CT optimal for characterization. The following discussion reviews factors used to differentiate between the benign and malignant lesion. Of those listed below, the two primary criteria are rate of growth/stability over time and the attenuation of the nodule.

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Table 18.3

CAUSES OF A SOLITARY PULMONARY MASS

Bronchial carcinoma Bronchial carcinoid Granuloma Hamartoma Metastasis Chronic pneumonia or abscess Hydatid cyst Pulmonary haematoma Bronchocele Fungus ball Massive fibrosis in coal workers Bronchogenic cyst Sequestration Atriovenous malformation Pulmonary infarct Round atelectasis

Table 18.4

SIMULANTS OF A SOLITARY PULMONARY MASS

Extrathoracic artefacts Cutaneous masses Bony lesions Pleural tumours or plaques



PULMONARY NEOPLASMS

Attenuation and enhancement The attenuation of a pulmonary nodule on CT can be classified as soft tissue, calcification, fat and ground glass. A dense central nidus or laminated calcification are good indications of a granulomatous process (tuberculosis, histoplasmosis). Irregular ‘popcorn’ calcification is very suggestive of a hamartoma, but is comparatively uncommon in such tumours when they are less than 30 mm in diameter. Granular calcification on CT is seen in up to 7% of carcinomas, usually in large rather than small tumours. Sometimes the calcification represents tumour calcification, sometimes it is due to benign granulomatous calcification engulfed by a carcinoma. CT is of most value for the detection of fat, its presence being virtually diagnostic of hamartoma (present in 20–30% of cases). A lack of enhancement (< 15 HU) following an intravenous bolus of contrast medium is also indicative of benignity138 (Fig. 18.36). Recent studies of screening CT have found that mixed soft tissue and ground-glass attenuation nodules have a greater likelihood of malignancy compared to soft tissue nodules, and that groundglass attenuation nodules when malignant are more likely to be of bronchiolo-alveolar carcinoma cell type17.

Size The size of the mass is of little diagnostic value. Although only a small percentage of nodules under 1 cm in diameter are malignant, over 40% of malignant nodules are less than 2 cm and 15% are less than 1 cm in diameter15,139.

Encysted pleural fluid Pulmonary vessels

The age of the patient is also a significant distinguishing feature. Only 1% of solitary masses in patients under the age of 35 years will be carcinomas.

Margins The features of the margins of the mass are of some predictive value and are best demonstrated by high-resolution CT15. Carcinomas typically have ill-defined margins which are irregular, speculated, or lobulated and may exhibit umbilication or a notch. Unfortunately all these features can be seen with benign disease. On the other hand, a well-defined mass

Rate of growth/stability over time Considerable amounts of data have been accumulated on the growth rates of benign and malignant masses. The measure of growth is the volume doubling time. Benign lesions almost invariably have a doubling time of less than 1 month or more than 18 months, with the volume doubling time for most peripheral pulmonary carcinomas being between 1 and 18 months (median 3 months)134–136. Bronchiolo-alveolar carcinomas are an exception; they may grow slowly, with volume doubling times much longer than those usually quoted for bronchial carcinoma137. Monitoring of growth by serial radiography is now not recommended, but these data serve to underline the fact that a mass which has demonstrably not changed in size over a period of 2 years can be regarded as almost certainly benign, and emphasize the importance of obtaining old images for comparison wherever possible. Volumetric analysis tools on CT provide a more accurate determination of interval growth. Growth in and of itself does not indicate malignancy, but does increase the likelihood that a nodule is malignant.

Figure 18.36 Contrast-enhanced CT for the evaluation of a solitary pulmonary nodule. There is differential enhancement in this lesion that was due to a primary adenocarcinoma.

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with a perfectly smooth, pencil-sharp margin is unlikely to be bronchial carcinoma, although a metastasis may occasionally exhibit these features. PET or PET–CT has been shown to have sensitivity, specificity and accuracy of 90% or greater in the diagnosis of benign nodules133. False-positive results may occur in patients with infectious or inflammatory processes, and false-negative results may occur in slow growing malignancies such as bronchiolo-alveolar carcinoma. PET also has difficulty evaluating lesions less than 10 mm in diameter. In a patient with a known extrathoracic primary malignancy the lesion should be considered as a probable metastasis. There is no place for searching for an occult extrapulmonary primary malignancy which, as the source of an isolated metastasis, accounts for only 2% of all solitary pulmonary masses. Such a search is far more fruitfully conducted after surgical excision or needle biopsy of the mass, when there will be some indication of the primary site from the histology available. Sputum cytology provides a low yield in solid, as opposed to cavitating, masses, but is easy to perform and may provide a definitive diagnosis of malignancy. Whilst percutaneous biopsy has an extremely low falsepositive rate for malignancy (well under 1%), the false-negative rate is around 10%. Other limitations of the technique are the low yield of a specific diagnosis of many benign lesions and the imperfect correlation of cell type between the cytological sample and the eventual histology. Most of these series, however, relied on FNA cytology. Improved diagnostic rates of benign pathology may be achieved with cutting needle biopsy techniques140.

Summary When a solitary pulmonary mass is detected every attempt should be made to obtain old images to check for interval change in size. The margins of the lesion and the presence or absence of calcification should be assessed. This frequently involves the use of CT which may also demonstrate specific signs of a benign lesion (atriovenous malformation, bronchocele and fungus ball). Lesions that are unchanged in size over a 2-year period may be presumed to be benign and followed up at 6-monthly intervals for a further 2 years. The presence of central or ringlike calcification also places the lesion in the benign category. Solitary pulmonary masses in patients under 40 years of age which are truly spherical with a clear-cut margin are unlikely to be malignant. Whilst it may be difficult to firmly establish the benign nature of the lesion in this way, the absence of evidence of malignancy in a satisfactory specimen allows a ‘wait and see’ policy in some patients. The other indications for biopsy are a presumed solitary metastasis; a presumed bronchial carcinoma when thoracotomy is inadvisable owing to the general health of the patient or is contraindicated because the lesion is unresectable or there are known metastases; and for the investigation of the solitary pulmonary mass occurring in the immunosuppressed patient.

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70. Valk P E, Pounds T R, Hopkins D M 1995 Staging non-small cell lung cancer by whole-body positron emission tomographic imaging. Ann Thorac Surg 60: 1573–1582 71. Dietlein M, Weber K, Gandjour A et al 2000 Cost-effectiveness of FDGPET for the management of solitary pulmonary nodules: a decision analysis based on cost reimbursement in Germany. Eur J Nucl Med 27: 1441–1456 72. Potchen E J, Bisesi M A 1990 When is it malpractice to miss lung cancer on chest radiographs? Radiology 175: 29–32 73. Woodring J H 1990 Pitfalls in the radiologic diagnosis of lung cancer. Am J Roentgenol 154: 1165–1175 74. Muhm J R, Miller W E, Fontana R S, Sanderson D R, Uhlenhopp M A 1983 Lung cancer detected during a screening program using fourmonth chest radiographs. Radiology 148: 609–615 75. Heelan R T, Flehinger B J, Melamed M R et al 1984 Non-small cell lung cancer: results of the New York screening program. Radiology 151: 289–293 76. Lemlich G, Schwam L, Lebwohl M 1987 Kaposi’s sarcoma and acquired immunodeficiency syndrome. Postmortem findings in twenty-four cases. J Am Acad Dermatol 16: 319–325 77. Nash G, Fligiel S 1984 Kaposi’s sarcoma presenting as pulmonary disease in the acquired immunodeficiency syndrome: diagnosis by lung biopsy. Hum Pathol 15: 999–1001 78. Davis S D, Henschke C I, Chamides B K, Westcott J L 1987 Intrathoracic Kaposi sarcoma in AIDS patients: Radiographic pathologic correlation. Radiology 163: 495–500 79. Sivit C J, Schwartz A M, Rockoff S D 1987 Kaposi’s sarcoma of the lung in AIDS: radiologic–pathologic analysis. Am J Roentgenol 148: 25–28 80. Naidich D P, Tarras M, Garay S M, Birnbaum B, Rybak B J, Schinella R 1989 Kaposi’s sarcoma. CT–radiographic correlation. Chest 96: 723–728 81. Huang R M, Naidich D P, Lubat E, Schinella R, Garay S M, McCauley D I 1989 Septic pulmonary emboli: CT–radiographic correlation. Am J Roentgenol 153: 41–45 82. Zibrak J D, Silvestri R C, Costello P et al 1986 Bronchoscopic and radiologic features of Kaposi’s sarcoma involving the respiratory system. Chest 90: 476–479 83. Hannon F B, Easterbrook P J, Padley S, Boag F, Goodall R, Phillips R H 1998 Bronchopulmonary Kaposi’s sarcoma in 106 HIV-1 infected patients. Int J STD AIDS 9: 518–525 84. Gelder C M, Hetzel M R 1993 Primary tracheal tumours: a national survey. Thorax 48: 688–692 85. Allen M S 1993 Malignant tracheal tumors. Mayo Clin Proc 68: 680–684 86. Choplin R H, Kawamoto E H, Dyer R B, Geisinger K R, Mills S E, Pope T L 1986 Atypical carcinoid of the lung: radiographic features. Am J Roentgenol 146: 665–668 87. Altman R L, Miller W E, Carr D T, Payne W S, Woolner L B 1973 Radiographic appearance of bronchial carcinoid. Thorax 28: 433–434 88. Forster B B, Muller N L, Miller R R, Nelems B, Evans K G 1989 Neuroendocrine carcinomas of the lung: clinical, radiologic, and pathologic correlation. Radiology 170: 441–445 89. Nessi R, Basso R P, Basso R S, Bosco M, Blanc M, Uslenghi C 1991 Bronchial carcinoid tumors: radiologic observations in 49 cases. J Thorac Imaging 6: 47–53 90. Zwiebel B R, Austin J H, Grimes M M 1991 Bronchial carcinoid tumors: assessment with CT of location and intratumoral calcification in 31 patients. Radiology 179: 483–486 91. Carney J A 1983 The triad of gastric epithelioid leiomyosarcoma, pulmonary chondroma, and functioning extra-adrenal paraganglioma: a five-year review. Med Balt 62: 159–169 92. Mazas-Artasona L, Romeo M, Felices R et al 1988 Gastro-oesophageal leiomyoblastomas and multiple pulmonary chondromas: an incomplete variant of Carney’s triad. Br J Radiol 61: 1181–1184 93. Bateson E M, Abbott E K 1960 Mixed tumors of the lung, or hamartochondromas. A review of the radiological appearances of cases published in the literature and a report of fifteen new cases. Clin Radiol 11: 232–247 94. Poirier T J, van Ordstrand H S 1971 Pulmonary chondromatous hamartomas. Report of seventeen cases and review of the literature. Chest 59: 50–55

95. Siegelman S S, Khouri N F, Scott W W Jr et al 1986 Pulmonary hamartoma: CT findings. Radiology 160: 313–317 96. Martin E 1983 Leiomyomatous lung lesions: a proposed classification. Am J Roentgenol 141: 269–272 97. Morgan D E, Sanders C, McElvein R B, Nath H, Alexander C B 1992 Intrapulmonary teratoma: a case report and review of the literature. J Thorac Imaging 7: 70–77 98. Muller N L, Fraser R S, Lee K S, Johkoh T 2003 Diseases of the Lungs, 1st edn. Lippincott Williams & Wilkins, Philadelphia 99. Katzenstein A L, Gmelich J T, Carrington C B 1980 Sclerosing hemangioma of the lung: a clinicopathologic study of 51 cases. Am J Surg Pathol 4: 343–356 100. Sugio K, Yokoyama H, Kaneko S, Ishida T, Sugimachi K 1992 Sclerosing hemangioma of the lung: radiographic and pathological study. Ann Thorac Surg 53: 295–300 101. Kwong J S, Muller N L, Miller R R 1992 Diseases of the trachea and main-stem bronchi: correlation of CT with pathologic findings. RadioGraphics 12: 645–657 102. McCarthy M J, Rosado-de-Christenson M L 1995 Tumors of the trachea. J Thorac Imaging 10: 180–198 103. Johkoh T, Muller N L, Pickford H A et al 1999 Lymphocytic interstitial pneumonia: thin-section CT findings in 22 patients. Radiology 212: 567–572 104. Howling S J, Hansell D M, Wells A U, Nicholson A G, Flint J D, Muller N L 1999 Follicular bronchiolitis: thin-section CT and histologic findings. Radiology 212: 637–642 105. Filly R, Bland N, Castellino R A 1976 Radiographic distribution of intrathoracic disease in previously untreated patients with Hodgkin’s disease and non-Hodgkin’s lymphoma. Radiology 120: 277–281 106. Cobby M, Whipp E, Bullimore J, Goodman S, Davies E R, Goddard P 1990 CT appearances of relapse of lymphoma in the lung. Clin Radiol 41: 232–238 107. Jenkins P F, Ward M J, Davies P, Fletcher J 1981 Non-Hodgkin’s lymphoma, chronic lymphatic leukaemia and the lung. Br J Dis Chest 75: 22–30 108. Au V, Leung A N 1997 Radiologic manifestations of lymphoma in the thorax. Am J Roentgenol 168: 93–98 109. Lee K S, Kim Y, Primack S L 1997 Imaging of pulmonary lymphomas. Am J Roentgenol 168: 339–345 110. Dunnick N R, Parker B R, Castellino R A 1976 Rapid onset of pulmonary infiltration due to histiocytic lymphoma. Radiology 118: 281–285 111. King L J, Padley S P, Wotherspoon A C, Nicholson A G 2000 Pulmonary MALT lymphoma: imaging findings in 24 cases. Eur Radiol 10: 1932–1938 112. Lee D K, Im J G, Lee K S et al 2000 B-cell lymphoma of bronchusassociated lymphoid tissue (BALT) : CT features in 10 patients. J Comput Assist Tomogr 24: 30–34 113. Wislez M, Cadranel J, Antoine M et al 1999 Lymphoma of pulmonary mucosa-associated lymphoid tissue: CT scan findings and pathological correlations. Eur Respir J 14: 423–429 114. Bragg D G 1987 Radiology of the lymphomas. Curr Probl Diagn Radiol 16: 177–206 115. Maile C W, Moore A V, Ulreich S, Putman C E 1983 Chest radiographic– pathologic correlation in adult leukemia patients. Invest Radiol 18: 495–499 116. Heyneman L E, Johkoh T, Ward S, Honda O, Yoshida S, Muller N L 2000 Pulmonary leukemic infiltrates: high-resolution CT findings in 10 patients. Am J Roentgenol 174: 517–521 117. Siegel M J, Shackelford G D, McAlister W H 1981 Pleural thickening. An unusual feature of childhood leukemia. Radiology 138: 367–369 118. Neiman R S, Barcos M, Berard C et al 1981 Granulocytic sarcoma: a clinicopathologic study of 61 biopsied cases. Cancer 48: 1426–1437 119. Lee M J, Grogan L, Meehan S, Breatnach E 1991 Pleural granulocytic sarcoma: CT characteristics. Clin Radiol 43: 57–59 120. van Buchem M A, Wondergem J H, Kool L J et al 1987 Pulmonary leukostasis: radiologic-pathologic study. Radiology 165: 739–741

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121. Vernant J P, Brun B, Mannoni P, Dreyfus B 1979 Respiratory distress of hyperleukocytic granulocytic leukemias. Cancer 44: 264–268 122. Coppage L, Shaw C, Curtis A M 1987 Metastatic disease to the chest in patients with extrathoracic malignancy. J Thorac Imaging 2: 24–37 123. Chaudhuri M R 1970 Cavitary pulmonary metastases. Thorax 25: 375–381 124. Ishihara T, Kikuchi K, Ikeda T, Yamazaki S 1973 Metastatic pulmonary diseases: biologic factors and modes of treatment. Chest 63: 227–232 125. Schaner E G, Chang A E, Doppman J L, Conkle D M, Flye M W, Rosenberg S A 1978 Comparison of computed and conventional whole lung tomography in detecting pulmonary nodules: a prospective radiologic-pathologic study. Am J Roentgenol 131: 51–54 126. Janower M L, Blennerhassett J B 1971 Lymphangitic spread of metastatic cancer to the lung. A radiologic–pathologic classification. Radiology 101: 267–273 127. Johkoh T, Ikezoe J, Tomiyama N et al 1992 CT findings in lymphangitic carcinomatosis of the lung: correlation with histologic findings and pulmonary function tests. Am J Roentgenol 158: 1217–1222 128. Munk P L, Muller N L, Miller R R, Ostrow D N 1988 Pulmonary lymphangitic carcinomatosis: CT and pathologic findings. Radiology 166: 705–709 129. Ren H, Hruban R H, Kuhlman J E et al 1989 Computed tomography of inflation-fixed lungs: the beaded septum sign of pulmonary metastases. J Comput Assist Tomogr 13: 411–416 130. Stein M G, Mayo J, Muller N, Aberle D R, Webb W R, Gamsu G 1987 Pulmonary lymphangitic spread of carcinoma: Appearance on CT scans. Radiology 162: 371–375 131. Baumgartner W A, Mark J B 1980 Metastatic malignancies from distant sites to the tracheobronchial tree. J Thorac Cardiovasc Surg 79: 499–503 132. Chan C K, Hutcheon M A, Hyland R H, Smith G J, Patterson B J, Matthay R A 1987 Pulmonary tumor embolism: a critical review of clinical, imaging, and hemodynamic features. J Thorac Imaging 2: 4–14



PULMONARY NEOPLASMS

133. Hartman T E 2005 Radiologic evaluation of the solitary pulmonary nodule. Radiol Clin North Am 43: 459–465, vii 134. Hayabuchi N, Russell W J, Murakami J 1983 Slow-growing lung cancer in a fixed population sample. Radiologic assessments. Cancer 52: 1098–1104 135. Nathan M H, Collins V P, Adams R A 1962 Differentiation of benign and malignant pulmonary nodules by growth rate. Radiology 79: 221–232 136. Steele J D, Buell P 1973 Asymptomatic solitary pulmonary nodules. Host survival, tumor size, and growth rate. J Thorac Cardiovasc Surg 65: 140–151 137. Hill C A 1984 Bronchioloalveolar carcinoma: a review. Radiology 150: 15–20 138. Swensen S J, Morin R L, Schueler B A et al 1992 Solitary pulmonary nodule: CT evaluation of enhancement with iodinated contrast material—a preliminary report. Radiology 182: 343–347 139. Gurney J W 1993 Determining the likelihood of malignancy in solitary pulmonary nodules with Bayesian analysis. Part I. Theory. Radiology 186: 405–413 140. McLoud T C 1998 Should cutting needles replace needle aspiration of lung lesions? Radiology 207: 569–570

SUGGESTIONS FOR FURTHER READING Hansell D M, Armstrong P, Lynch D A, McAdams H P 2005 Imaging of diseases of the chest, 4th edn. Elsevier, Philadelphia Muller N L, Fraser R S, Lee K S, Johkoh T 2003 Diseases of the lung, 1st edn. Lippincott Williams & Wilkins, Philadelphia

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High-Resolution Computed Tomography of Interstitial and Occupational Lung Disease

19

David M. Hansell, Zelena A. Aziz and Nestor L. Müller

• High-resolution computed tomography patterns of interstitial lung disease • Idiopathic interstitial pneumonias • Sarcoidosis • Hypersensitivity pneumonitis • Langerhans cell histiocytosis • Lymphangioleiomyomatosis • Connective tissue diseases • Systemic vasculitides • Drug-induced lung disease • Occupational lung disease

The pulmonary interstitium is the network of connective tissue fibres that supports the lung. It includes the alveolar walls, interlobular septa and the peribronchovascular interstitium. The term interstitial lung disease (ILD) is used to refer to a group of disorders that mainly affects these supporting structures. Although the majority of these disorders also involve the airspaces, the predominant abnormality is thickening of the interstitium which may be due to the accumulation of fluid, cells, or fibrous tissue. The chest radiograph remains part of the initial assessment of ILD, but the radiographic pattern is often non-specific, observer variation is considerable1 and it is relatively insensitive to early ILD2–4. High-resolution computed tomography (HRCT) has revolutionized the imaging of ILD as it enables early detection of disease, allows a histospecific diagnosis to be made in certain cases, and provides insight into disease reversibility and prognosis.

HIGH-RESOLUTION COMPUTED TOMOGRAPHY PATTERNS OF DIFFUSE LUNG DISEASE Diffuse abnormalities of the lung on HRCT may be broadly classified into one of the following four patterns: (A) reticular

or linear; (B) nodular; (C) ground-glass opacity through to consolidation; and (D) areas of decreased lung attenuation.

Reticular pattern A reticular pattern on CT almost always represents significant ILD. Morphologically, a reticular pattern may be caused by thickened interlobular or intralobular septa or honeycomb (fibrotic) destruction. Numerous thickened interlobular septa indicate an extensive interstitial abnormality and causes include infiltration by fibrosis (interstitial fibrosis), abnormal cells (lymphangitis carcinomatosa), or fluid (pulmonary oedema). Although thickened interlobular septa can be a consequence of infiltration by fibrosis, this feature is not a frequent finding in idiopathic pulmonary fibrosis (IPF). Interlobular septal thickening is usually described as smooth (seen in pulmonary oedema and alveolar proteinosis) or irregular (lymphangitic spread of tumour), but the distinction is not always easily made. Sarcoidosis causes nodular septal thickening although this pattern is not usually the dominant feature5. Intralobular septal thickening manifests as a fine reticular pattern on HRCT and is seen in all ILDs but most commonly in IPF. Often, the intralobular septal thickening may be so fine that HRCT does not demonstrate discrete intralobular opacities but a generalized increase in lung density (ground-glass opacification). Severe pulmonary fibrosis usually results in a coarse reticular pattern made up of interlacing irregular linear opacities. The reticular pattern of end-stage fibrotic (honeycomb) lung is characterized by cystic airspaces surrounded by irregular walls. The distortion of normal lung morphology by extensive fibrosis results in irregular dilatation of segmental and subsegmental airways (traction bronchiectasis/bronchiolectasis); in the periphery of the lung, it can be difficult to distinguish dilated airways from true honeycomb change.

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Nodular pattern A nodular pattern is a feature of both interstitial and airspace disease.The distribution and density of nodules can help narrow what can be a lengthy differential diagnosis. Nodules within the lung interstitium, especially those related to the lymphatic vessels, are seen in the interlobular septa, subpleural and peribronchovascular regions; a distribution seen most commonly in sarcoidosis but also in lymphangitis carcinomatosa. Centrilobular nodules are seen in several conditions (Table 19.1). In particular, distinguishing between subacute hypersensitivity pneumonitis and respiratory bronchiolitis–interstitial lung disease (RB–ILD) can be difficult, because both cause relatively low density, poorly defined centrilobular nodules which may look identical on HRCT. A random distribution of very small well-defined nodules is seen in patients with haematogenous spread of tuberculosis, pulmonary metastases, pneumoconiosis and rarely in pulmonary sarcoidosis.

lung disease. In the first two processes, the decreased attenuation (‘black’) lung is abnormal; in infiltrative lung disease it is the ‘grey’ lung that is abnormal. In a study of 70 patients in whom a mosaic attenuation pattern was the dominant abnormality, Worthy et al showed that small airways disease and infiltrative lung disease were correctly identified but the mosaic attenuation pattern caused by occlusive vascular disease was frequently misinterpreted6. Bronchial abnormalities and the presence of air trapping on expiratory CT are the most useful discriminatory features in identifying small airways disease as the cause of mosaic attenuation. However, the phenomenon of hypoxic bronchodilatation in chronic occlusive vascular disease7, and the demonstration that air trapping is seen on expiration in acute pulmonary embolism8 complicates the interpretation. Nevertheless, the differentiation between the three basic causes of a mosaic attenuation pattern is usually easily made when clinical and physiological information is taken into account.

Ground-glass pattern A ground-glass pattern on HRCT is defined as a generalized increase in opacity that does not obscure pulmonary vessels. At a microscopic level, the changes responsible for ground-glass opacity are complex and include partial filling of the airspaces, considerable thickening of the interstitium, or a combination of the two. Ultimately though, the pattern of groundglass opacity on HRCT results from displacement of air from the lungs. Many conditions result in the non-specific pattern of ground-glass opacity but the most common causes include subacute hypersensitivity pneumonitis, acute respiratory distress syndrome (ARDS), acute interstitial pneumonia (AIP), non-specific interstitial pneumonia (NSIP) and diffuse pneumonias, particularly Pneumocystis jirovecii (carinii) pneumonia in patients with acquired immune deficiency syndrome (AIDS). The definite identification of dilated airways within areas of ground glass is usually an indication of fine fibrosis and thus usually indicates irreversible disease. The caveat is that, in certain entities (e.g. organizing pneumonia), dilated airways that are present within areas of ground glass in the acute setting may completely resolve following successful treatment.

Mosaic attenuation pattern The term mosaic attenuation pattern refers to regional attenuation differences demonstrated on HRCT.The attenuation of a given area of lung depends on the amount of blood, parenchymal tissue and air in that area, and thus the sign of a mosaic attenuation pattern is non-specific. It is the dominant abnormality in three completely different types of diffuse pulmonary disease: small airways disease, occlusive vascular disease and infiltrative

Table 19.1 CONDITIONS CHARACTERIZED BY PROFUSE CENTRILOBULAR NODULES IN HRCT Subacute hypersensitivity pneumonitis Respiratory bronchiolitis–interstitial lung disease Diffuse panbronchiolitis Endobronchial spread of tuberculosis or bacterial pneumonia Cryptogenic organizing pneumonia (unusual pattern)

IDIOPATHIC INTERSTITIAL PNEUMONIAS The term idiopathic interstitial pneumonia (IIP) is applied to a group of disorders with no known cause, and with more or less distinct histological and radiological appearances. Over the years, there have been additions and subtractions to the classification, but in 2001 an American Thoracic Society (ATS)/ European Respiratory Society (ERS) consensus panel consisting of clinicians, radiologists and pathologists sought to clarify the nomenclature by combining the histopathological pattern seen on lung biopsy with clinical and radiological features9. The current classification of IIPs is outlined in Table 19.2. Current guidelines recommend a multidisciplinary approach to the diagnosis of the IIPs and a recent study has demonstrated that dynamic interaction between clinicians, radiologists and pathologists improves interobserver agreement and diagnostic confidence10.

Usual interstitial pneumonia/idiopathic pulmonary fibrosis Usual interstitial pneumonia (UIP) is the most common histopathological pattern in patients with the clinical presentation of cryptogenic fibrosing alveolitis (CFA)/IPF. Under the new classification, the term IPF is exclusively reserved for patients with the idiopathic clinical syndrome associated with the morphological pattern of UIP. Other causes of a UIPtype pattern on histology include chronic hypersensitivity pneumonitis, asbestosis, connective tissue disease and rarely drugs. The pathological features of UIP are the presence of fibroblastic foci, normal areas, dense fibrosis and honeycombing; the crucial finding is of areas of fibrosis at different stages of maturity. The number of fibroblastic foci on lung biopsy is an important predictor of survival11. Classic chest radiographic features include bilateral asymmetric peripheral reticular opacities most profuse at the lung bases associated with lung volume loss, although in the presence of coexisting emphysema, lung volumes may be preserved or increased. The characteristic and virtually pathognomonic appearance of IPF on HRCT is of a predominantly subpleural bibasal

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HIGH-RESOLUTION COMPUTED TOMOGRAPHY OF INTERSTITIAL AND OCCUPATIONAL LUNG DISEASE

Table 19.2 HISTOLOGICAL AND CLINICAL CLASSIFICATION OF THE IDIOPATHIC INTERSTITIAL PNEUMONIAS Clinico–radiological–pathological criteria

Histological pattern

HRCT features

Idiopathic pulmonary fibrosis

Usual interstitial pneumonia

Reticular opacities Honeycombing Areas of ground-glass opacity associated with traction bronchiectasis

Non-specific interstitial pneumonia

Non-specific interstitial pneumonia

Areas of ground-glass opacity ± traction bronchiectasis Honeycombing minimal

Cryptogenic organizing pneumonia

Organizing pneumonia

Peripheral or peribronchial consolidation Areas of ground-glass opacity Perilobular pattern (increasingly recognized)

Acute interstitial pneumonia

Diffuse alveolar damage

Consolidation (dependent lung) Areas of ground-glass opacity Traction bronchiectasis (organizing phase)

Respiratory bronchiolitis–interstitial lung

RB–ILD

disease (RB–ILD)

Poorly defined centrilobular nodules Areas of ground-glass opacity Bronchial wall thickening Limited emphysema

Desquamative interstitial pneumonia (DIP)

DIP

Areas of ground-glass opacity Features of interstitial fibrosis

Lymphoid interstitial pneumonia (LIP)

LIP

Areas of ground-glass opacity Centrilobular nodules Thickened interlobular septa Thin-walled discrete cysts

reticular pattern within which there are areas of honeycomb destruction (Fig. 19.1)12. As the disease progresses, it often appears to ‘creep’ around the periphery of the lung to involve the anterior aspects of the upper lobes (Fig. 19.2); the finding of upper lobe irregularities (reticulation) is an important discriminator between UIP and other conditions with similar

Figure 19.1 Usual interstitial pneumonia. HRCT abnormalities predominate in the posterior, subpleural regions of the lower lobes and comprise honeycombing and traction bronchiectasis within the abnormal lung.

clinical presentations13. In the study by Hunninghake et al, the presence of both honeycombing and upper lobe irregularities increased the specificity for UIP from 69% (honeycombing alone) to 81%13. The presence of ground-glass opacification is not a dominant feature and when present, there is usually obvious traction bronchiectasis and bronchiolectasis. Mediastinal lymphadenopathy (up to 2 cm) unrelated to infection or malignancy is a frequent accompaniment14.

Figure 19.2 Usual interstitial pneumonia. In the upper lobes anteriorly there are peripheral irregular lines with areas of honeycombing.

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Studies have demonstrated that when a confident diagnosis of IPF is made on HRCT, the diagnosis is invariably correct15,16, and it has been suggested that a confident diagnosis of IPF made by experienced observers should obviate biopsy16. HRCT also has a role in predicting survival. A study by Flaherty et al suggested that patients with histological UIP who had definite or probable UIP by HRCT criteria had a worse prognosis than those who had interdeterminate HRCT findings17. The rapid development of a diffuse increase in the attenuation of lung parenchyma in patients with IPF should raise the possibility of an opportunistic infection (such as PCP), an accelerated phase of the disease (Fig. 19.3)18, or concurrent pulmonary oedema. Other complications include lung cancer19 and pulmonary tuberculosis (Fig. 19.4); the latter usually has atypical appearances on CT due to the presence of underlying lung fibrosis20.

Figure 19.4 Tuberculosis on a background of usual interstitial pneumonia. Biopsy of the area of consolidation in the right lower lobe confirmed tuberculosis.

Non-specific interstitial pneumonia NSIP is characterized by varying degrees of interstitial inflammation and fibrosis without the specific features that allow a diagnosis of UIP or desquamative interstitial pneumonia (DIP)21. While NSIP may have significant fibrosis, it is usually of uniform temporality (in comparison to UIP), and fibroblastic foci and honeycombing, if present, are scanty. Although the clinical features of NSIP resemble those of UIP, prognosis is considerably better22,23. Non-idiopathic NSIP is most often found on lung biopsy in patients with connective tissue disease and may be the pattern identified in some cases of drug-induced lung disease and hypersensitivity pneumonitis. On HRCT, NSIP is characterized by a predominant pattern of ground-glass opacification in a predominantly basal and subpleural distribution with or without associated distortion of airways (Fig. 19.5). A reticular pattern is common but honeycombing is sparse or absent24. In general, NSIP may be distinguished from UIP on CT by a more prominent component of ground-glass attenuation and a finer reticular pattern in the absence of honeycombing25. However, the variability of CT appearances reflects the heterogeneity of the pathological processes encompassed by NSIP and a confident diagnosis of NSIP based on CT alone is less readily made than in cases of UIP. Consolidation is reportedly a highly variable feature (0–98%24,25) and this discrepancy probably reflects the fact that some patients with non-idiopathic NSIP have significant amounts of histological organizing pneumonia, making classification of individual cases difficult.

Cryptogenic organizing pneumonia Figure 19.3 Usual interstitial pneumonia. HRCT performed (A) before and (B) after clinical deterioration in a patient with biopsy proven usual interstitial pneumonia. HRCT obtained during the accelerated phase of the disease demonstrates a generalized increase in lung attenuation and progression of both the reticular and honeycomb patterns.

A component of organizing pneumonia is identifiable in a variety of different contexts, including infection26, malignancy27, drug-related lung injury28 and in association with connective tissue disease29. However, in 1983, Davison et al30 described a clinicopathological entity of isolated organizing pneumonia in patients without an identifiable associ-

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HIGH-RESOLUTION COMPUTED TOMOGRAPHY OF INTERSTITIAL AND OCCUPATIONAL LUNG DISEASE

distribution is typically seen in patients with polymyositis or dermatomyositis. Ground-glass opacification, subpleural linear opacities and a distinctive perilobular pattern (Fig. 19.7)34 are also commonly encountered. The histopathological appearance of organizing pneumonia is a uniform temporal appearance of mild interstitial chronic inflammation associated with an intraluminal organizing fibrosis in distal airspaces. The lung architecture is generally well preserved. A complete response to a long (2–3 months) course of high-dose steroid treatment is the general rule, although in a minority of patients the process progresses with the incorporation of the organizing pneumonia into the alveolar walls as mature fibrosis35.

Respiratory bronchiolitis–interstitial lung disease and desquamative interstitial pneumonia

Figure 19.5 Non-specific interstitial pneumonia. The predominant abnormality is patchy, bilateral ground-glass opacification, mild reticulation and traction bronchiectasis. There is no frank honeycombing destruction.

ated disease. In 1985, Epler et al31 described the same entity and used the term bronchiolitis obliterans organizing pneumonia (BOOP). The ATS/ERS Consensus statement9 recommends that the term cryptogenic organizing pneumonia (COP) be used because it avoids confusion with airway diseases such as constrictive obliterative bronchiolitis. On a chest radiograph the most frequent feature of COP is patchy, often subpleural and basal, areas of consolidation with preservation of lung volumes. The areas of airspace consolidation have a propensity to progress and change location over time. On HRCT, consolidation corresponding to areas of organizing pneumonia is the cardinal feature found more frequently in the lower zones, with either a subpleural or a peribronchial distribution (Fig. 19.6)32,33; the peribronchial

Figure 19.6 Cryptogenic organizing pneumonia. HRCT through the upper lobes demonstrates areas of consolidation in a subpleural and peribronchial distribution in association with areas of ground-glass opacification (left upper lobe).

These two entities are considered together because of their strong association with cigarette smoking. All cigarette smokers have, to some degree, inflammation around their small airways (‘respiratory bronchiolitis’) but this is clinically unimportant and not considered further here. Patients generally present with an insiduous onset of dyspnoea and cough. The chest radiograph is relatively insensitive for the detection of RB–ILD and DIP and a normal chest radiograph has been reported in up to 20% of patients with RB–ILD36 and 25% in DIP37. On HRCT, the features of RB–ILD include areas of patchy ground-glass opacification (resulting from macrophage accumulation within alveolar spaces and alveolar ducts) and poorly defined low attenuation centrilobular nodules (Fig. 19.8). In addition, upper lobe centrilobular emphysema, usually of very limited extent and areas of air trapping, reflecting that the bronchiolitic element of this entity may be present38. Some patients show thickening of the interlobular septa and features of interstitial fibrosis, but this is unusual36. Ground-glass opacification is also the dominant feature seen in DIP (Fig. 19.9). The distribution is typically

Figure 19.7 Biopsy proven organizing pneumonia. There are poorly defined arcade-like and polygonal opacities (the perilobular pattern) in the subpleural and posterior regions of both lungs. The opacities resemble ill-defined thickened interlobular septa.

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Figure 19.8 Respiratory bronchiolitis–interstitial lung disease. HRCT shows (A) subtle areas of ground-glass opacification and (B) ill-defined centrilobular nodules.

and Langerhans cell histiocytosis (LCH) and interstitial fibrosis, the global term smoking related-interstitial lung disease (SRILD) has been proposed to encompass DIP, RB–ILD, LCH and interstitial fibrosis (Fig. 19.10)36,40,41.

Acute interstitial pneumonia

Figure 19.9 Several areas of non-specific ground-glass opacification in the right middle lobe and both lower lobes.

lower zone, peripheral and may be patchy39. In some patients there are HRCT features of established fibrosis (in the form of architectural distortion with dilatation of some bronchi), usually of limited extent. The majority of patients with DIP or RB–ILD have a relatively stable clinical course. Smoking cessation is an important part of the management of patients but the influence of smoking on the clinical course of these patients has not been fully delineated; some patients have persistent abnormalities on HRCT even with smoking cessation and corticosteroid therapy. Because of the significant overlap between the clinical, imaging and histological features of DIP and RB–ILD and to a lesser extent between these two patterns

Acute interstitial pneumonia (AIP) can be regarded as an idiopathic form of the ARDS and is histologically (and clinically) distinct from the other interstitial pneumonias. The histological pattern seen in AIP is that of diffuse alveolar damage (DAD), which is also found in infection, connective tissue disease, drug toxicity, toxic inhalation, uraemia and sepsis. DAD has an acute exudative phase and a subsequent organizing and fibrotic phase. Lung biopsy shows diffuse involvement with temporal homogeneity, which may imply lung injury due to a single event42. The chest radiograph shows bilateral patchy airspace opacification43. HRCT demonstrates a combination of ground-glass opacification, consolidation, bronchial dilatation and architectural distortion44. Ground-glass opacification on HRCT is found in all three phases of AIP, but coexistent traction bronchiectasis probably reflects the incorporation of established fibrosis in the proliferative and fibrotic phases45. Follow-up CT studies in survivors demonstrate clearing of the ground-glass attenuation and consolidation, leaving reticular opacities consistent with residual fibrosis. Anterior nondependent fibrotic damage in survivors secondary to barotrauma has also been reported46.

Lymphoid interstitial pneumonia The term lymphoid interstitial pneumonia (LIP) was proposed by Liebow and Carrington47 to describe a disease entity characterized by a widespread interstitial lymphoid infiltrate

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HIGH-RESOLUTION COMPUTED TOMOGRAPHY OF INTERSTITIAL AND OCCUPATIONAL LUNG DISEASE

Figure 19.10 Smoking related-interstitial lung disease. Images of the (A) upper and (B) lower lobes of a 42 year old man with a 25-pack year smoking history and dyspnoea. The combination of a fine reticular pattern representing fibrosis and ground-glass opacification on a background of emphysema suggests a diagnosis of smoking related-interstitial lung disease.

of the lung, resembling lymphoma but with a clinical course more akin to a chronic interstitial pneumonia. Although in the past LIP has been considered by some to be a pulmonary lymphoproliferative disorder, evolution to frank lymphoproliferative disease is rare and thus LIP remains within the group of interstitial pneumonias9. Classically, LIP occurs in association with autoimmune diseases, most often Sjögren’s syndrome. Other diseases associated with LIP include dysproteinaemias, autologous bone marrow transplantation and viral, mycobacterial and human immunodeficiency virus (HIV) infections. Intrathoracic Castleman’s disease is frequently associated with LIP48. The incidence of LIP is approximately two-fold greater in women and symptoms of progressive cough and dyspnoea usually predominate. Common HRCT findings are nodules of varying sizes (which may be ill-defined), areas of groundglass opacification, thickened bronchovascular bundles, interlobular septal thickening and thin-walled cysts (1–30 mm) (Fig. 19.11)49,50. Airspace disease, large nodules and pleural effusions are rare in these patients. The cysts in LIP are usually discrete, are not found in clusters and are found deep within the lung parenchyma49. The cysts have been postulated to result from the lymphocytic infiltrate compressing bronchioles, causing stenosis or obstruction and subsequent postobstructive bronchiolar ectasia.

SARCOIDOSIS Sarcoidosis is a multisystem granulomatous disorder of unknown aetiology. As a consequence, the diagnosis of this syndrome is defined by the presence of characteristic clinical and radiological data along with histological evidence of noncaseating granuloma. Granulomas in the lung have a characteristic distribution along the lymphatics in the bronchovascular sheath and, to a lesser extent, in the interlobular septa and subpleural lung regions. Sarcoidosis is a disease of young

Figure 19.11 Lymphocytic interstitial pneumonitis. There is a background of ground-glass opacification and a few thin-walled cystic airspaces (the pathogenesis of these cysts is unclear).

adults, with a peak incidence in the second to fourth decades. The hilar and mediastinal nodes and the lungs are affected clinically much more commonly than any other organ or system. They are followed in decreasing order of frequency by the skin (26%), peripheral lymph nodes (22%), eyes (15%), spleen (6%), central nervous system (4%), parotid glands (4%) and bones (3%)51. Pulmonary involvement accounts for most of the morbidity and mortality associated with sarcoidosis. Sarcoidosis is traditionally staged according to its appearance on the chest radiograph: stage I, lymphadenopathy; stage II, lymphadenopathy with parenchymal opacity; stage III, parenchymal opacity alone52. Low stages at presentation are reported to have a

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better prognosis than high stages, although the precision and clinical usefulness of such ‘staging’ is questionable.

Lymphadenopathy Sarcoidosis is characterized by bilateral, symmetrical hilar and paratracheal lymphadenopathy. Some degree of lymphadenopathy is evident on a chest radiograph in about 70–80% of patients at some time during the course of the condition. Hilar lymph node enlargement ranges from the barely detectable to the massive and gives the hila a lobulated and usually well-demarcated outline. Occasionally hilar lymphadenopathy appears to be asymmetrical or, in 1–5% of cases, may even be strictly unilateral although this is distinctly unusual53,54. Marked asymmetry that is confirmed by CT is sufficiently unusual to bring the diagnosis into question. Clinically significant compression of adjacent airways, arteries and veins is extremely unusual, even though lymph node enlargement is often massive. Paratracheal lymphadenopathy may be bilateral or unilateral and in the latter instance is usually right sided. The most common manifestation of left-sided lymphadenopathy is enlargement of the aortopulmonary window nodes—a common and characteristic feature on the chest radiograph. Other mediastinal nodes (anterior prevascular, posterior and subcarinal) are often not identified as being enlarged on the chest radiograph but on CT are seen to be affected in about half of patients55. In 90% of patients with lymphadenopathy, nodal enlargement is maximal on the first radiograph and usually disappears within 6–12 months. In about 5%, however, large nodes persist more or less indefinitely and these can be a source of confusion. Recurrence of lymphadenopathy is exceedingly rare. The lymph nodes may calcify, sometimes in a characteristic eggshell fashion. This latter feature is shared by only a few conditions (Table 19.3). Although lymph node calcification is seen on the radiograph in 5% or less of patients with sarcoidosis, it may be evident on CT in up to 40% of patients with long-standing disease56. The calcification is of variable intensity but may be relatively light, and the affected lymph nodes are usually small in volume and evenly distributed throughout the mediastinum and hila (very different from calcified nodes due to tuberculous infection which usually follow a drainage path)57. About 40% of patients presenting with nodal enlargement will develop parenchymal opacities, usually within a year, and of these about one-third will go on to have persistent (fibrotic) shadowing. Nodal enlargement does not develop after parenchymal opacities have appeared.

Table 19.3 CAUSES OF EGGSHELL NODAL CALCIFICATION Sarcoidosis Silicosis Histoplasmosis Lymphoma (postirradiation) Blastomycosis Amyloidosis

Parenchymal changes Parenchymal changes probably occur histologically in all patients but are only detected on the chest radiograph in 50–70% of cases. Characteristically, parenchymal abnormalities appear as the nodal enlargement is subsiding (in lymphoma such abnormalities tend to progress in unison).The most common radiographic pattern, seen in 75–90% of patients with parenchymal opacities, is of rounded or irregular nodules 2– 4 mm in diameter, which are usually moderately well defined. Smaller or larger opacities are not uncommon, though they rarely exceed 5 mm.Very small aggregated opacities sometimes give a ground-glass appearance. All zones tend to be affected but there is usually a mid and upper zonal predominance. The second most common pattern, seen in 10–20% of patients with parenchymal opacity, is patchy airspace consolidation. Opacities sometimes contain air bronchograms and have ill-defined margins that commonly break up into a nodular pattern. They tend to involve predominantly the peribronchovascular regions of the middle and upper lungs zones, although they may be diffuse or, occasionally, have a subpleural predominance. The parenchymal opacities described above will clear completely in about two-thirds of cases and progress to fibrosis in one-third. Permanent fibrotic shadowing is unusually coarse with a mid and upper zone predominance. The radiographic pattern consists of coarse linear opacities with evidence of volume loss and ring shadowing caused by bullae or traction bronchiectasis. Occasionally a conglomerate opacity develops resembling progressive massive fibrosis. Cor pulmonale, bullous disease with or without mycetoma formation, and pneumothorax are all recognized complications of this fibrotic stage.

High-resolution computed tomography features Parenchymal opacities are well demonstrated on HRCT (Fig. 19.12)5,58 and HRCT appearances have a high sensitivity and specificity for the diagnosis. The most consistent pulmonary parenchymal abnormality is the presence of nodular opacities (1–5 mm) distributed in a perilymphatic fashion, predominantly along the bronchovascular bundles and subpleurally and, to a lesser extent, along interlobular septa. Other findings include irregular and beaded interfaces, larger ill-defined nodules with/without an air bronchogram, patchy groundglass opacities and occasional interlobular septal thickening. In advanced disease there is evidence of fibrosis, predominantly in the perihilar regions of the middle and upper lung zones (Fig. 19.13). Air trapping is a common HRCT feature of sarcoidosis and its presence shows a good correlation with indices of small airways disease on pulmonary function tests59.The combination of a peribronchovascular, subpleural distribution, small well-defined nodules, fibrosis and a mid and upper zone distribution has been highlighted as the features most helpful in making a diagnosis of sarcoidosis. In a very small number of cases, sarcoidosis has been shown to mimic IPF with intralobular septal thickening and ground-glass opacity seen predominantly in the basal subpleural regions of the lung60. Despite the better delineation of parenchymal disease on HRCT, it is not recommended as part of the initial diagnostic work-up in patients with suspected sarcoidosis; its greatest use being

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Figure 19.12



HIGH-RESOLUTION COMPUTED TOMOGRAPHY OF INTERSTITIAL AND OCCUPATIONAL LUNG DISEASE

Sarcoidosis. Typical HRCT features are (A) nodular opacities which (B) may become confluent, and (C) interlobular septal thickening.

They are seen most often in the context of established disease and are subacute, lasting weeks or months. The prevalence of effusions is about 2%.

Bronchial stenosis and airflow obstruction Mild large airway narrowing may be due to nodal compression, but significant lesions are usually due to intrinsic mural sarcoidosis. Stenoses may be single or multiple and particularly affect larger airways to segmental level65. Such stenoses are very rare but can cause significant airflow obstruction or atelectasis, particularly in the middle lobe. However, the functional severity of airflow obstruction seems to be largely determined by the extent of a reticular pattern, representing established fibrosis, on HRCT66.

Figure 19.13 Fibrotic sarcoidosis. There are areas of conglomerate fibrosis in a perihilar distribution with associated bronchial distortion and volume loss. The appearances superficially mimic progressive massive fibrosis seen in the pneumoconioses.

in patients who present with an atypical chest radiograph61. Previous HRCT studies have shown that areas of parenchymal consolidation and ground-glass opacity are usually reversible, whereas little resolution is identified following treatment in patients with reticulation and architectural distortion56,62. Despite this distinction between reversible and irreversible disease on HRCT, studies comparing HRCT assessment of disease activity to clinical, scintigraphic and bronchoscopic findings have yielded contradictory results63,64. Hence, HRCT is not generally used to guide prognosis in patients with sarcoidosis.

Other thoracic findings Pleural thickering and effusions Pleural thickening and effusions are unusual manifestations of sarcoidosis and do not occur in isolation. Effusions, though commonly unilateral, may be bilateral and are usually small.

HYPERSENSITIVITY PNEUMONITIS Hypersensitivity pneumonitis, also known as extrinsic allergic alveolitis, is an immunologically mediated lung disease characterized by an inflammatory reaction to specific antigens contained in a variety of organic dusts67. Common causes include avian proteins (e.g. bird breeder’s lung) and thermophilic bacteria present in mouldy hay (farmer’s lung), mouldy grain (grain handler’s lung), or heated water reservoirs (humidifier or air conditioner lung). A more comprehensive list is given in Table 19.4. These antigens reach the alveoli where they provoke an immunological reaction that includes both type III (immune complex response) and type IV (cell-mediated) mechanisms. The cell-mediated response results in a delayed hypersensitivity reaction and the presence of granulomatous inflammation within the pulmonary interstitium. Interestingly, several studies have shown that cigarette smoking has a suppressive effect that interferes with the immunopathological process that ultimately leads to hypersensitivity pneumonitis68,69. The clinical features of hypersensitivity pneumonitis are characteristic. Approximately 6 h after exposure the patient develops fever, chills, dyspnoea and cough.There is no eosinophilia, and

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Table 19.4 MAJOR CAUSES OF HYPERSENSITIVITY PNEUMONITIS Agent

Source

Disease

Aspergillus

Mouldy hay

Farmer's lung

Thermophilic actinomyces

Compost

Mushroom worker's lung

Trichosporum asahii

Tatami mats

Japanese summer-type hypersensitivity pneumonitis

Isocyanates

Paint sprays, plastics Isocyanate hypersensitivity pneumonitis

Mycobacterium avium complex

Hot tubs

Unknown

Metal working fluids Metal worker's lung

Bird proteins

Bird feathers, excrement

Hot tub lung

Bird fancier's lung

wheeze is not a prominent feature. The radiological findings are influenced by the stage of the disease. A chest radiograph taken during the acute episode can be normal70, but typical radiographic findings include diffuse ground-glass opacification and a fine nodular or reticulonodular pattern; these two features become more prominent in the subacute phase71. Between acute attacks the radiograph may return to normal and the fluctuating nature of changes on serial radiographs is highly suggestive of the diagnosis. In chronic hypersensitivity pneumonitis, fibrosis with upper lobe retraction, reticular opacity, volume loss and honeycombing may be seen. On HRCT, the nodules of hypersensitivity pneumonitis are typically poorly defined, < 5 mm in diameter72, centrilobular70 and seen throughout the lung, although a mid to lower lung zone predominance has been variably reported (Fig. 19.14)73. Ground-glass opacity is most common in the acute phase but may also be a feature of subacute and chronic hypersensitivity pneumonitis, especially if there is ongoing exposure74. A mosaic attenuation pattern is common in hypersensitivity pneumonitis; the presence of lobular areas of decreased vascularity that show air trapping on expiratory HRCT, reflecting the coexisting bronchiolitis caused by antigen deposition in the small airways (Fig. 19.15)75. The combination on HRCT

Figure 19.14 Subacute extrinsic allergic alveolitis. HRCT shows numerous poorly defined, relatively low attenuation nodules.

Figure 19.15 Hypersensitivity pneumonitis. (A) Inspiratory image shows patchy density differences reflecting both the interstitial infiltrate of subacute hypersensitivity pneumonitis and coexisting small airways disease. (B) End-expiratory image enhances the density differences revealing several secondary pulmonary lobules of decreased attenuation.

of features of infiltrative (ill-defined nodules and ground-glass opacity) and small airways disease may be remarkably similar to that seen in patients with RB–ILD; however, the distinction can usually be made with knowledge of the smoking history. Lymph node enlargement (smaller than 20 mm) has been described in both acute and subacute hypersensitivity pneumonitis14, and the presence of thin-walled lung cysts is also an occasional feature in subacute hypersensitivity pneumonitis. Cysts range in size from 3 to 25 mm and resemble those seen in lymphocytic interstitial pneumonia76, although their pathogenesis remains uncertain. Emphysema is a reported sequela of farmer’s lung and a study has demonstrated that in hypersensi-

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tivity due to farmer’s lung, emphysema was a more prominent feature than honeycombing/fibrosis (even in never smokers) and was seen in approximately one-third of patients74. This is in comparison to pigeon breeder’s disease, where lung fibrosis is the major complication. The chronic stage of hypersensitivity pneumonitis is characterized by fibrosis, although evidence of active disease is often present. Radiological findings include intralobular and interlobular interstitial thickening, traction bronchiectasis and honeycomb destruction (Fig. 19.16)77. In some cases, there is a mid zone predominance, but the fibrotic appearance may be seen in the upper or lower lobes73. Patients with hypersensitivity pneumonitis may exhibit histological and imaging features of NSIP78,79 or UIP80,81, and thus should be considered as a differential diagnosis when either IPF or NSIP is being considered on HRCT appearances. Imaging

Figure 19.16 Chronic hypersensitivity pneumonitis. The reticular pattern with distortion of the lung parenchyma indicates established fibrosis in this case of chronic hypersensitivity pneumonitis.

features that favour hypersensitivity pneumonitis over IPF include an upper or mid zone predominance, the presence of ground-glass opacity and air trapping81.

LANGERHANS CELL HISTIOCYTOSIS Langerhans cell histiocytosis (LCH), formerly known as pulmonary histiocytosis X or eosinophilic granuloma of the lung, is a granulomatous disorder characterized histologically by the presence of large histiocytes containing rod- or racket-shaped organelles (Langerhans cells)67. The male-to-female ratio is about 4:1, and the vast majority of adult patients are cigarette smokers. In the earliest stages, patients are often asymptomatic. Others present with dyspnoea, cough, constitutional symptoms or a spontaneous pneumothorax. Pulmonary involvement is widespread, bilateral and usually symmetrical. At presentation, usually because of dyspnoea or a pneumothorax, the chest radiograph is abnormal. Typical appearances are of reticulonodular shadowing in the mid and upper zones of the lungs that are of normal or increased volume82. The nodules vary in size from micronodular to approximately 1 cm in diameter and, although histopathological examination will often demonstrate cavitation83, this feature is often difficult to appreciate on chest radiography. The classical appearances of LCH on HRCT are nodules (ranging in size from a few millimetres to 2 cm), several of which show cavitation (this feature often clinches the diagnosis) and have bizarre shapes (Fig. 19.17). At this stage of the disease, there are no obvious features of fibrosis. The distribution of disease is a useful diagnostic pointer and the typical sparing of the extreme lung bases and anterior tips of the right middle lobe and lingula is preserved even in end-stage disease84. The typical nodules of LCH85 tend to show a predictable progression through the following stages: cavitation of the nodules, thin-walled cystic lesions, and finally emphysematous and fibrobullous destruction86.

Figure 19.17 Langerhans cell histiocytosis. (A) Shows the characteristic combination of thin-walled cysts and poorly defined nodules, some of which are just beginning to cavitate. (B) Image from a patient with more advanced disease. There are numerous irregularly-shaped cysts bilaterally and a pneumothorax on the right.

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LYMPHANGIOLEIOMYOMATOSIS Lymphangioleiomyomatosis (LAM) is a disease characterized histologically by two key features: cysts and proliferation of atypical smooth muscle cells (LAM cells) of the pulmonary interstitium, particularly in the bronchioles, pulmonary vessels and lymphatics67. LAM is a rare disease seen almost exclusively in women, the vast majority of cases being diagnosed during childbearing age. Similar pulmonary abnormalities can be seen in approximately 1% of patients with tuberous sclerosis. The most commonly described radiographic manifestation of LAM is a pattern of generalized, symmetrical, reticular, or reticulonodular opacities with normal or increased lung volumes87,88. Pleural effusions occur in 10–40% of patients89–91 (these may be unilateral or bilateral) and pneumothoraces in approximately 50% of cases.The effusions are chylous and result from involvement of the thoracic duct by the leiomyomatous tissue. The CT manifestations of LAM are distinctive, characterized by numerous thin-walled cysts randomly distributed throughout the lungs with no zonal predilection92 (Fig.19.18). Imaging features that help distinguish LAM from LCH include a more diffuse distribution of cysts typically with no sparing of the bases, more regularly shaped cysts and normal intervening lung parenchyma. Occasionally HRCT may demonstrate interlobular septal thickening88 (attributed to dilatation of lymphatic channels secondary to obstruction of pleuropulmonary lymphatics) or patchy areas of ground-glass attenuation (presumably the result of pulmonary haemorrhage)89.

in each disease separately, depending upon whether imaging, physiological, or histological criteria are used to judge involvement. Although the radiographic and HRCT appearances are not specific for any of the collagen vascular disorders, they frequently provide good corroborative evidence in substantiating what is often a difficult clinical diagnosis.

Rheumatoid disease Rheumatoid arthritis (RA) is a connective tissue disease characterized by a symmetrical inflammatory arthritis. The majority of patients have extra-articular disorders, thus the term rheumatoid disease is commonly used to emphasize the systemic nature of the disorder. RA is associated with a broad spectrum of pleural and pulmonary manifestations. Most, but not all, patients with pleuropulmonary disease have other clinical evidence of RA. In a significant minority of patients with rheumatoid disease, pleuropulmonary disease antedates the development of arthritis and in general, pleuropulmonary involvement is not related to the severity of the arthritis. The most frequently encountered manifestations of rheumatoid disease in the chest are listed in Table 19.5. Pleural involvement, either manifesting as effusions or thickening, is common. Pleural effusions can be unilateral or bilateral, are usually small or moderate in size, and the majority resolve spontaneously93.

Table 19.5 INTRATHORACIC MANIFESTATIONS OF RHEUMATOID DISEASE Pleural effusion or thickening

CONNECTIVE TISSUE DISEASES

Interstitial fibrosis (most frequently usual interstitial pneumonia type) Constrictive obliterative bronchiolitis

The connective tissue diseases form a heterogeneous group of chronic inflammatory and immunologically mediated disorders, all of which affect the lung and pleura to a variable extent and in various ways. Although the lung is a particularly vulnerable target organ, the frequency of pleuropulmonary involvement varies widely within the spectrum of disease and also

Bronchiectasis Organizing pneumonia Follicular bronchiolitis Drug-induced lung disease (methotrexate) Necrobiotic nodules/Caplan's syndrome

Figure 19.18 Lymphangioleiomyomatosis. (A) There is a profusion of thin-walled cystic airspaces scattered evenly throughout the lungs. The cysts are relatively uniform in size. (B) In a more advanced case of LAM, note the small left-sided pleural effusion.

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HIGH-RESOLUTION COMPUTED TOMOGRAPHY OF INTERSTITIAL AND OCCUPATIONAL LUNG DISEASE

ILD in RA is more common in men with seropositive disease. The most common histopathological pattern in RA-associated ILD is UIP with HRCT features that are indistinguishable from idiopathic cases; namely reticular opacities with honeycombing predominantly in the subpleural regions of the lung (Fig. 19.19)94. It is thought that the prognosis for RA–ILD is better than for idiopathic cases; Flaherty et al have demonstrated that patients with a connective tissue disease-associated UIP pattern had fewer fibroblastic foci and better survival when compared with patients with the idiopathic type95. NSIP is also seen but is less prevalent than in the other connective tissue diseases such as systemic sclerosis. Other pulmonary abnormalities seen in RA include follicular bronchiolitis, bronchiectasis (in up to 30% of cases) (Fig. 19.20)96,97, obliterative bronchiolitis (this

Figure 19.19 Rheumatoid arthritis with a usual interstitial pneumonia (UIP)-type pattern. In this case the HRCT appearances of peripheral reticular abnormality and honeycombing are indistinguishable from that of UIP.

can occur in patients who are on penicillamine, gold or no treatment)98, methotrexate-induced pneumonitis and organizing pneumonia94. Rheumatoid (necrobiotic) pulmonary nodules are an uncommon feature of the disease.They are usually associated with the presence of subcutaneous nodules, and like them may wax and wane. They may be single or multiple, vary in size from a few millimetres to several centimetres, are well circumscribed and may cavitate99.They are usually asymptomatic and may occur in association with pulmonary fibrosis and pleural changes. Radiologically identical nodules, characteristically appearing rapidly and in crops, may occur in patients with rheumatoid arthritis who have been exposed to silica. Radiographic findings of pneumoconiosis may be present but usually are not a prominent feature100. This phenomenon was originally described in Welsh coalminers (Caplan’s syndrome). These nodules contain dust particles and are quite different from necrobiotic nodules on histological examination. Follicular bronchiolitis (discussed here because of its frequent association with rheumatoid disease) is part of the spectrum of lymphoproliferative disease and is characterized histologically by a diffuse peribronchiolar proliferation of hyperplastic lymphoid follicles and mild, if any, alveolar interstitial inflammation101. Clinically the patients usually present during young adulthood or middle age with insidious dyspnoea102. Most cases of follicular bronchiolitis are associated with connective tissue disease, especially RA, Sjögren’s syndrome and scleroderma, but it is also seen in association with immunodeficiency syndromes including AIDS, pulmonary infections, or ill-defined hypersensitivity reactions. The cardinal features of follicular bronchiolitis on HRCT consist of centrilobular nodules measuring 1–12 mm in diameter, variably associated with peribronchial nodules and patchy areas of ground-glass opacity103. Nodules and ground-glass opacities are generally bilateral and diffuse in distribution. Mild bronchial dilatation with wall thickening and a tree-inbud pattern are less frequent findings104.

Sjögren’s syndrome

Figure 19.20 Rheumatoid arthritis. HRCT demonstrates both mild cylindrical bronchiectasis and constrictive obliterative bronchiolitis (reflected by areas of low attenuation in which there is a reduction in the number of vessels present) in this patient with rheumatoid arthritis.

Sjögren’s syndrome (SjS) is a chronic autoimmune inflammatory disease characterized by a triad of clinical features: dry mouth (xerostomia), dry eyes (keratoconjunctivitis sicca) and arthritis105. SjS can occur alone as primary SjS or in association with other autoimmune diseases—secondary SjS. A recent study evaluating the radiological and pathological manifestations of lung diseases associated with primary SjS found that NSIP was the most common entity; other pathologies included bronchiolitis, lymphoma, amyloid and atelectasis106. HRCT studies have demonstrated LIP in patients with Sjögren’s syndrome107,108; the imaging findings of which are described under the section on the IIPs. The association of LIP and amyloidosis (manifesting on HRCT as multiple irregular nodules) in patients with SjS is recognized (Fig. 19.21)107, but as these patients are also at increased risk of pulmonary lymphoma108, the finding of LIP on HRCT in conjunction with multiple nodules in a patient with SjS should at least prompt the consideration of a neoplastic process.

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Figure 19.21 Sjögren’s syndrome—lymphoid interstitial pneumonia and amyloid. There are numerous thin-walled cysts in association with multiple irregular solid nodules, some of which are heavily calcified. Histopathological examination showed marked thickening of the interstitium with an infiltrate of small, mature lymphocytes and plasma cells. Multiple deposits of amyloid were seen throughout the specimen and there was no evidence of malignancy.

Progressive systemic sclerosis (scleroderma) Progressive systemic sclerosis (SSc) is a collagen vascular disease characterized by the deposition of excessive extracellular matrix with vascular occlusion involving several organs. It commonly affects the skin (scleroderma), peripheral vasculature, kidneys, oesophagus and lungs. As with systemic lupus erythematosus, SSc occurs more frequently in women. Cutaneous features dominate the clinical picture, at least in the early stages, although the prognosis is usually determined by involvement of the heart, lungs and kidneys. ILD is common in patients with SSc and causes considerable morbidity and

mortality. The interstitium and pulmonary vasculature are the predominant sites that are affected109,110. The HRCT findings of interstitial fibrosis in SSc include peripheral reticular opacities, ground-glass attenuation associated with traction bronchiectasis and occasionally honeycomb destruction111,100. At microscopy, NSIP is increasingly regarded as the more prevalent histological pattern in patients with SSc112,113, and indeed CT studies have confirmed that patients with SSc typically have HRCT features more akin to idiopathic NSIP with a less coarse fibrosis when compared with IPF and a greater proportion of ground-glass opacification (Fig. 19.22)114. A UIP pattern is thought to occur in 5–10% of cases113. Pleural disease is much less common in SSc than in other connective tissue diseases; pleural thickening being seen on HRCT in approximately 10% of patients115. As in other diffuse fibrosing lung diseases, enlarged mediastinal lymph nodes (which histologically show reactive hyperplasia) are a frequent finding on CT116.

Polymyositis/dermatomyositis Polymyositis (PM) is an idiopathic autoimmune inflammatory myopathy that results in proximal muscle weakness117. Dermatomyositis (DM) is similar except that it is accompanied by a skin rash. Pulmonary complications of PM/DM are important determinants of the clinical course with aspiration pneumonia being the most important pulmonary disease due to its prevalence as well as its associated morbidity and mortality118. Respiratory muscle weakness and a poor cough reflex are responsible for the high prevalence of recurrent aspiration. ILD in PM/DM was first described in 1956119 and occurs in an estimated 5–47% of patients. Initial clinical presentation is with cough, dyspnoea and fever, prior to musculoskeletal manifestations of arthralgia, myalgia and weakness in 30%, with simultaneous occurrence in only 20%120. NSIP is thought to

Figure 19.22 Scleroderma. (A,B) Two patients with scleroderma showing ground-glass opacification in association with traction bronchiectasis and a fine reticular pattern. The pattern of fibrosis is closest to that of non-specific interstitial pneumonia. Note the dilated oesophagus in both examples.

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HIGH-RESOLUTION COMPUTED TOMOGRAPHY OF INTERSTITIAL AND OCCUPATIONAL LUNG DISEASE

be the most common histological pattern seen in PM/DM120. The ILD can be acute and aggressive, similar to AIP, with some series reporting up to 10.5% mortality29,121, or more slowly progressive. In some, the lung disease is responsive to steroids and immunosuppression121. At presentation, the most common HRCT features of PM/DM are linear opacities with a lower lung predominance, ground-glass opacities, irregular interfaces and areas of consolidation (Fig. 19.23). Parenchymal micronodules and honeycombing are less frequently observed29. Histologically, organizing pneumonia is the correlate of consolidation and ground-glass opacification seen on HRCT. DAD is demonstrated in some cases and is associated with widespread involvement, dense dependent consolidation and extensive diffuse ground-glass opacification. Organizing pneumonia in PM/DM can also be admixed with interstitial fibrosis with a predominance of reticular elements and architectural distortion, traction bronchiectasis and honeycombing, and this overlap entity is associated with a poor prognosis122. When comparing patients with PM/DM ILD as a whole, the 3-year survival is 74.7% and 5-year survival 60.4%120, which is better than in IPF, but not significantly different from patients with idiopathic NSIP.

Systemic lupus erythematosus Systemic lupus erythematosus (SLE) is a chronic multisystem disease of unknown origin characterized by the presence of autoantobodies against various cell nuclear antigens123. SLE is associated with widespread inflammatory changes in the connective tissues, vessels and serosal surfaces. Pleuropulmonary disease will occur in more than half of patients with SLE at some point during the course of their illness124. Although pleuritis is the most common manifestation of SLE, diverse thoracic manifestations which range from diaphragmatic dysfunction (shrinking lung syndrome) to life-threatening pneumonitis or

pulmonary haemorrhage are encountered. A list of the other pulmonary complications may be found in Table 19.6. Pleural effusions are the most common radiographic abnormality. They are frequently bilateral, usually only small in volume and, unlike those in rheumatoid disease, are often associated with pleuritic pain. Thick horizontal band shadows at the lung bases due to linear atelectasis may be secondary to the pleurisy or, more likely, restricted diaphragmatic movement. Pulmonary consolidation in patients with SLE may cause diagnostic difficulty as it may be a consequence of infection (the incidence of respiratory tract infection in patients with SLE is high due to the immunological abnormalities, immunosuppression from steroids and respiratory muscle weakness), pulmonary oedema, lupus pneumonitis, or pulmonary haemorrhage. Pulmonary oedema may be secondary to renal

Table 19.6 INTRATHORACIC MANIFESTATIONS OF SYSTEMIC LUPUS ERYTHEMATOSUS Pleural effusion Segmental or subsegmental collapse Lupus pneumonitis Pulmonary infection Pulmonary oedema Diaphragmatic dysfunction Interstitial fibrosis (rare) Pericardial effusion Pulmonary vascular disease Pulmonary arterial hypertension Vasculitis/capillaritis Pulmonary embolism Pulmonary veno-occlusive disease

Figure 19.23 Polymyositis/dermatomyositis. HRCT features include (A) reticular opacities and (B) areas of ground-glass opacification. The appearances of (B) are compatible with organizing pneumonia being incorporated as fibrosis.

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disease or cardiac failure. Acute lupus pneumonitis is a wellrecognized but rare manifestation of the disease that is characterized by fever, severe hypoxaemia and diffuse pulmonary infiltrates125. Radiological features are typically patchy consolidation and focal atelectasis seen predominantly in the lower lung zones with concomitant pleural effusions. Histological findings are not diagnostic but include alveolar wall damage, inflammatory cell infiltration and haemorrhage125. Compared with many other collagen vascular diseases, SLE is not commonly associated with chronic diffuse ILD. When present, reported HRCT findings include irregular linear and bandlike opacities (in part atelectasis), ground-glass opacities and interlobular septal thickening. Honeycombing which can resemble IPF is extremely rare100. Loss of lung volume is sometimes a prominent feature and is secondary to a myopathy of the diaphragmatic muscle. Diffuse alveolar haemorrhage is a rare but dramatic complication of SLE126, which manifests radiologically as widespread ground-glass opacity and consolidation. SLE is associated with increased risk of malignancy, with lymphoma being the most common124.

Ankylosing spondylitis Ankylosing spondylitis is a chronic inflammatory disease that affects mainly the axial skeleton, particularly the costovertebral, apophyseal and sacroiliac joints127. The majority of patients with ankylosing spondylitis have airway and interstitial abnormalities evident on HRCT, but these are usually mild and seldom evident on the chest radiograph128. Apical fibrosis, evident on chest radiography, is seen in approximately 1% of patients100. The upper lobe fibrosis causes upward retraction of the hila, and is often associated with bullous formation and apical pleural thickening. The changes are usually bilateral but may be unilateral, especially initially, and are indistinguishable from tuberculosis. Occasionally pulmonary changes may antedate the spondylitis. Ankylosing spondylitis is one of a number of causes (albeit a very rare one) of upper lobe fibrosis (Table 19.7). As with tuberculosis, mycetomas may form within the upper lobe cavities. The HRCT findings of ankylosing spondylitis include apical fibrosis, mild peripheral interstitial fibrosis, parenchymal bands, bronchiectasis and bullae128,129.

SYSTEMIC VASCULITIDES A number of disorders are characterized histologically by a systemic vasculitis in which the primary pathogenetic mechanism is the deposition of immune complexes in the walls of Table 19.7 CAUSES OF BILATERAL UPPER LOBE FIBROSIS Tuberculosis (including atypical mycobacterial infections) Sarcoidosis Histoplasmosis Allergic bronchopulmonary aspergillosis Chronic extrinsic allergic alveolitis Ankylosing spondylitis Progressive massive fibrosis (distinctive mass-like opacities)

blood vessels. The systemic vasculitides that most commonly affect the lung are Wegener’s granulomatosis, Churg–Strauss syndrome and Behçet’s disease. Only Churg–Strauss syndrome and Wegener’s granulomatosis will be covered in this section.

Wegener’s granulomatosis Wegener’s granulomatosis is a multisystem disease with variable clinical expression. It is characterized histologically by necrotizing granulomatous inflammation of the upper and lower respiratory tracts, the lungs being involved in approximately 90% of cases; focal necrotizing glomerulonephritis; and a small vessel vasculitis affecting arteries, capillaries and veins130. The majority of patients present with symptoms referable to the nose, paranasal sinuses, or chest; in some patients, the disease manifests solely in the respiratory tract and is known as limited (nonrenal) Wegener’s granulomatosis131. Chest symptoms include cough, dyspnoea, pleuritic chest pain and haemoptysis. Multiple nodules or masses are the most common imaging finding in Wegener’s granulomatosis, being seen in approximately 70% of cases132. Nodules range in size from a few millimetres to 10 cm, are frequently multiple, and increase in size and number as the disease progresses. Nodules are bilateral in 75% of cases, have no predilection for any lung zone, and usually show cavitation at about 2 cm in size133. HRCT may demonstrate nodules not apparent on radiography and is superior in demonstrating the presence of cavitation. Airspace consolidation and ground-glass opacities also may occur with or without the presence of nodules. Several patterns of consolidation have been described: (A) peripheral wedge-shaped lesions abutting the pleura mimicking pulmonary infarcts134; (B) a peribronchial distribution of consolidation135; and (C) a region of focal consolidation with or without cavitation (Fig. 19.24). Diffuse bilateral areas of ground-glass opacification are often a consequence of pulmonary haemorrhage132, but may also be related to necrotizing granulomatous inflammation similar to that associated with nodules. Rarely, Wegener’s granulomatosis may present as a fibrosing lung disease (closest to a UIP-type pattern) on HRCT136. Histopathologists have also described bronchocentric granulomatosis137 and organizing pneumonia138 in patients with Wegener’s granulomatosis, all of whom also demonstrated typical features of necrotizing vasculitis. Unilateral or bilateral pleural effusions are present in about 10% of patients and hilar or mediastinal lymphadenopathy has also been reported. Airway involvement is common in Wegener’s granulomatosis which may lead to subglottic, tracheal or bronchial narrowing (the latter resulting in segmental or lobar atelectasis). Mild bronchiectasis is an additional feature in Wegener’s granulomatosis occurring in up to 40% of cases134.

Churg–Strauss syndrome Churg–Strauss syndrome is an antineutrophil cytoplasmic antibody (ANCA)-associated systemic vasculitis affecting small arteries and veins. It is characterized histologically by the presence of necrotizing vasculitis and extravascular granulomatous inflammation rich in eosinophils, and clinically by the presence of asthma, fever and blood eosinophilia130. While the vasculitis affects both arteries and veins, predominant small vessel involvement is rarely encountered, and it is therefore not sur-

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Figure 19.24 Wegener’s granulomatosis. Images through the (A) mid and (B) upper zones in a patient with Wegener’s granulomatosis. Thick-walled cavitating mass in the left upper lobe (A). Note also the focal narrowing of the mid intrathoracic trachea (B) reflecting focal involvement by Wegener’s granulomatosis.

prising that diffuse pulmonary haemorrhage is an uncommon manifestation of Churg–Strauss syndrome. HRCT appearances largely reflect the eosinophilic infiltrate and are largely nonspecific. HRCT features include ground-glass opacities, areas of airspace consolidation, centrilobular nodules (some of which may display cavitation) and airways abnormalities attributable to asthma (Fig. 19.25)139. Histologically the airspace disease is due to eosinophilic infiltrate or foci of organizing pneumonia139. Interlobular septal thickening may be seen as a result of interstitial pulmonary oedema secondary to cardiac involvement. However, a significant proportion (up to 25%) of patients with Churg–Strauss syndrome have few or no imaging abnormalities and imaging is often of little help in making this somewhat elusive diagnosis. Even when HRCT abnormalities exist they

are not specific and the diagnostic accuracy for Churg–Strauss syndrome was less than 50% in one study140.

DRUG-INDUCED LUNG DISEASE The lung is less commonly the site of drug-induced disease than other organs such as the skin and gastrointestinal tract. Nevertheless, approximately 350 drugs can cause injury to the lungs, and the list of drugs and patterns of involvement continues to increase. Respiratory disease secondary to drugs may be the result of the pharmacological action of the drug in normal or excessive dosage, or caused by an allergic or idiosyncratic reaction. The radiological manifestations of drug-induced ILD, although heterogeneous and non-specific,

Figure 19.25 Churg–Strauss syndrome. Spectrum of HRCT features: (A) areas of ground-glass opacification, (B) small cavitating nodules,

Continued

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Figure 19.25, Cont’d (C) thickened interlobular septa, and (D) an area of airspace opacification, likely to be a peripheral infarct.

enable many alternative diagnoses to be excluded. There is no specific radiological pattern of parenchymal change associated with drug-induced lung disease and in the early stages of disease, patients with symptoms secondary to drug reaction may have a normal chest radiograph. Furthermore, data based on a small number of cases suggest that the different histological patterns of drug reaction are not always reflected by distinctive HRCT findings141. Despite these limitations, it is reasonable to understand the radiological manifestations of drug-induced lung disease via an appreciation of the underlying histological patterns of drug-induced disease142. The most common histological manifestations can be classified into DAD, chronic interstitial pneumonia (a vague term used by histopathologists which incorporates drug-induced lung disease with histologiTable 19.8

cal features that resemble either NSIP or less commonly UIP), hypersensitivity pneumonitis, organizing pneumonia and eosinophilic pneumonia142. Most drugs typically cause more than one type of histological pattern. Table 19.8 lists the drugs associated with the different histological patterns.

Diffuse alveolar damage Chemotherapeutic drugs such as busulphan, cyclophosphamide, carmustine (BCNU) and bleomycin constitute the largest group of drugs associated with this pattern of lung toxicity141. DAD usually develops a few weeks or months after initiating therapy and disease onset is heralded by progressive dyspnoea.The corresponding radiological features, not surprisingly, are similar to those found in ARDS with bilateral patchy or homogeneous

HISTOLOGICAL PATTERN OF DRUG-INDUCED LUNG DISEASE

Diffuse alveolar damage

Diffuse alveolar haemorrhage

Non-specific interstitial pneumonia

Organizing pneumonia

Eosinophilic pneumonia

Amiodarone

Amphotericin B

Amiodarone

Amiodarone

Ampicillin

Bleomycin

Cyclophosphamide

Carmustine

Carbamazepine

Captopril

Methotrexate

Nitrofurantoin

Busulphan

Interferon

Chlorpropamide

Nitrofurantoin

Amiodarone

Methotrexate

Methotrexate

Ethambutol

Carmustine

Anticoagulants

Nitrofurantoin

Sotalol

Indomethacin

Busulphan

Penicillamine

Melphalan

Nitrofurantion

Mesalazone

Sulphasalazine

Streptokinase

Phenytoin

Minocycline

Naproxen

Vinblastine

Haloperidol

Simvastatin

Phenytoin

Tetracycline Ranitidine Propranolol

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airspace consolidation involving mainly the middle and lower lung zones. HRCT demonstrates extensive bilateral groundglass opacities and dependent areas of airspace consolidation (Fig. 19.26)143. In most circumstances there are no histological features that allow separation of drug toxicity from other potential causes of DAD and the diagnosis of drug-induced lung disease requires vigorous exclusion of other potential aetiologies, most importantly opportunistic infection.

Non-specific interstitial pneumonia Drugs reported to cause an NSIP-type pattern include amiodarone, busulphan, carmustine, methotrexate, phenytoin and simvastatin142. Descriptions of HRCT findings are available for a limited number of agents, but demonstrate the same range of abnormalities described in patients with the idiopathic form of NSIP (Fig. 19.27)143,144. With disease progression, there may be evidence of fibrosis with development of a reticular pattern and traction bronchiectasis. The fibrosis is patchy in distribution and predominantly peribronchovascular,

a pattern most commonly seen in patients receiving nitrofurantoin. In some cases, however, HRCT features suggestive of irreversible fibrosis may show complete resolution on cessation of nitrofurantoin145. NSIP is the most common manifestation of amiodarone-induced lung disease146. HRCT features that have been described with amiodarone-induced lung disease include ground-glass opacities in association with fine intralobular reticulation seen predominantly in a peripheral distribution. Foci of consolidation have also been described147, and are likely to represent areas of organizing pneumonia.

Hypersensitivity pneumonitis Several drugs have been associated with a pattern of lung toxicity with radiological and histopathological features indistinguishable from hypersensitivity pneumonitis144, although in general, this pattern is an uncommon manifestation of drug-induced lung disease. Methotrexate is the best known offender; similar changes have been attributed to cyclophosphamide, fluoxetine, nitrofurantoin and amitriptyline. The radiological and HRCT findings are similar to those seen in hypersensitivity pneumonitis secondary to the inhalation of organic dust and consist of bilateral ground-glass opacities (Fig. 19.28) and/or small, poorly defined centrilobular nodular opacities141,144. HRCT and lung biopsies in methotrexate toxicity show features more characteristic of NSIP in the majority of patients with a pattern resembling hypersensitivity pneumonitis seen in only a few patients142.

Organizing pneumonia

Figure 19.26 Diffuse alveolar damage secondary to amiodarone. There is extensive bilateral ground-glass opacification and airspace consolidation. Note also the bilateral pleural effusions.

Figure 19.27 Non-specific interstitial pneumonia secondary to bleomycin. The dominant abnormality is ground-glass opacification in association with a fine reticular pattern. The pattern of fibrosis most closely resembles non-specific interstitial pneumonia.

An organizing pneumonia-like reaction has been reported most frequently in association with methotrexate, cyclophosphamide, gold, nitrofurantoin, amiodarone, bleomycin and busulphan141. The chest radiograph shows patchy bilateral areas of consolidation, masses or nodules, which may be asymmetric or symmetric. HRCT may demonstrate patchy asymmetrical ground-glass opacity and areas of consolidation which often have a predominantly peripheral or peribronchiolar distribution (Fig. 19.29)144.

Figure 19.28 Hypersensitivity pneumonitis secondary to sertraline. HRCT shows extensive bilateral ground-glass opacification and lobular areas of air trapping (arrows).

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Figure 19.29 Organizing pneumonia secondary to (A,B) nitrofurantoin and (C) amiodarone. The HRCT features of ground-glass opacification and consolidation (A,C) and a perilobular pattern (B) are in keeping with organizing pneumonia. The areas of consolidation in (C) are both peribronchial and perilobular in distribution.

Eosinophilic pneumonia Eosinophilic pneumonia is characterized histologically by the accumulation of eosinophils in the alveolar airspaces and infiltration of the adjacent interstitial space by eosinophils and variable numbers of lymphocytes and plasma cells. Peripheral blood eosinophilia is present in around 40% of patients. Eosinophilic pneumonia secondary to drug reaction is seen most commonly in association with methotrexate, sulphasalazine, para-aminosalicylic acid, nitrofurantoin and non-steroidal anti-inflammatory drugs. Chest radiography and HRCT show bilateral airspace consolidation, which tends to involve mainly the peripheral lung regions and the upper lobes141,143. The diagnosis of drug-induced disease will be missed unless specifically sought as a cause of unexplained diffuse pulmonary shadowing in patients at known risk with clinical symptoms of lung disease. It is particularly important, though often difficult, to differentiate between drug-induced disease, infections (particularly of the opportunistic variety) and metastatic malignancy in patients who are susceptible to a combination of these processes.

OCCUPATIONAL LUNG DISEASE Diseases of the lung caused by workplace and environmental exposures are common throughout both developed and developing worlds, and as industrial techniques continue to evolve, new occupational diseases will be recognized. The following section highlights the imaging features of the main pneumoconioses—silicosis, coal worker’s pneumoconiosis and asbestos-related pulmonary disease. Table 19.9 summarizes some of the other main occupational lung diseases. Hypersensitivity pneumonitis is covered in the preceding section on ILD. Work-related asthma is one of the most frequently reported occupational lung diseases in a number of industrialized countries148 but as these patients are not frequently imaged (and the contribution of imaging is negligible), this topic is not further discussed.

The International Labour Office Classification The International Labour Office (ILO) International Classification of Radiographs for the Pneumoconioses is a system

Table 19.9 EXAMPLES OF OCCUPATIONAL EXPOSURES THAT CAUSE LUNG PATHOLOGY Occupational lung disease Flock worker's lung

Pathology

Radiology

Lymphocytic bronchiolitis

Ground-glass opacities with centrilobular nodules181

Flavour worker's lung Obliterative (flavouring agents used bronchiolitis in microwave popcorn)

Mosaic attenuation pattern, air trapping, bronchial wall thickening182

Berylliosis

Noncaseating granulomas (indistinguishable from sarcoidosis) accompanied by mononuclear cell infiltrates and interstitial fibrosis

Nodules with a similar distribution to sarcoidosis, ground-glass opacities, thickened interlobular septa, reticular opacities and honeycombing (rare)183,184. Mediastinal adenopathy is less common than in sarcoidosis. Conglomerate masses are seen in advanced disease

Hard metal pneumoconiosis (alloys of tungsten carbide and cobalt, titanium and tantalum)

Giant cell interstitial pneumonia

Ground-glass attenuation and consolidation. Cysts and reticular abnormality may also occur185

used for the recording of chest radiographic abnormalities related to the inhalation of dusts. Its intent was to improve health workers’ health surveillance by facilitating international comparisons of pneumoconiosis statistics and research reports149. Thus, it was designed primarily for population epidemiology, rather than for individual diagnosis. In the ILO system, the size, shape and profusion of opacities on radiographs are classified in a detailed manner by trained observers using a set of standard radiographs. Rounded or nodular opacities are graded as p (< 1.5 mm diameter), q (1.5–3 mm), or r (3–10 mm). Irregular opacities are classified as s, t, or u, using the same size criteria. Large opacities (> 10 mm) are graded as A, B and C based on the combined dimensions of all large opacities present. The classification also scores the extent and thickness of plaques, pleural thickening, fissural thickening and

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calcified nodules. Profusion of the opacities is classified into four categories (0–3); category 0 indicating that there is no excess of small opacities above normal. The use of two profusion categories is useful when appearances lie between those of the standard radiographs. Thus, 1/0 indicates that appearances most closely resemble category 1, but that the reader has also considered category 0. Despite acknowledged limitations and problems with the ILO classification (interobserver variability, the presence of background opacities that are unrelated to dust exposure, the relative insensitivity of the chest radiograph to early disease, and the misuse of the classification in legal settlements for compensation), it remains a useful shorthand whose meaning is widely understood for population studies. HRCT classification systems for the pneumoconioses have been developed150, but it is too early to gauge whether such a classification will be widely accepted and adopted.

Silicosis/coal worker’s pneumoconiosis Silicon dioxide or silica is the most abundant mineral on earth and is formed from the elements silicon and oxygen under conditions of increased heat and pressure. Any occupation that disturbs the earth’s crust or exposes the worker to the use or processing of silica-containing rock or sand has potential risks. Mining, tunnelling through rock, quarrying, stone cutting and foundry work, amongst others, are potentially hazardous occupations. Coal worker’s pneumoconiosis (CWP) is a consequence of the inhalation of coal dust. Both coalmine dust and silica predispose workers to chronic bronchitis, simple pneumoconiosis, emphysema, complicated pneumoconiosis (progressive massive fibrosis [PMF]), lung cancer (in excess of that expected from smoking alone) and mycobacterial pulmonary infection—the risk for tuberculosis is increased three-fold in patients with chronic silicosis151. As coal also contains a variable proportion of quartz, it has often been difficult to separate the pulmonary effects of coal dust from that of silica; in general, coal of high rank (high carbon content), such as anthracite, is associated with a higher incidence of CWP. Silica causes three distinct clinical patterns of lung disease (Table 19.10) which are related to both level and duration of exposure. The earliest radiographic changes of silicosis and CWP are nearly identical. Typical appearances are a profusion

Table 19.10 EXPOSURE

of small (1–3 mm) round nodules distributed in the posterior aspects of the upper two-thirds of the lung152. Radiologically, the only difference between simple CWP and simple silicosis is that the nodules in CWP are often smaller (typically p, rather than q opacities, according to the ILO classification). With advancing disease, the nodules increase in size and number to involve all lung zones. The nodules are sometimes calcified. Hilar and mediastinal lymph node enlargement with calcification of the eggshell type is not uncommon and may be seen on the chest radiograph or CT. On CT, the micronodules are sharply defined and distributed throughout the lungs but are frequently most numerous in the upper lung zones. The nodules may be centrilobular or subpleural in location; the subpleural micronodules may become confluent, forming a ‘pseudo-plaque’153. PMF refers to the coalescence of large nodules and is much more common in silicosis than in CWP. On the chest radiograph, PMF is seen as mass-like opacities, typically in the posterior upper lobes and associated with contraction of the upper lobes and hilar elevation. Sequential evaluation of these masses often demonstrates migration towards the hila, leaving a peripheral rim of cicatricial emphysema. The outer margins of PMF often parallel the contour of the adjacent chest wall. CT confirms the architectural distortion associated with PMF (Fig. 19.30). Large lesions (> 5 cm) often show irregular low attenuation regions on CT indicative of necrosis. Frank cavitation is a less frequent finding and when present should always raise the suspicion of tuberculosis (conventional or atypical). Unilateral or asymmetric PMF may be distinguished from lung cancer by the presence of lobar volume loss and peripheral emphysema. Acute silicoproteinosis develops after exposure to high concentrations of crystalline silica. The dominant feature is the presence of an alveolar proteinaceous exudate, similar to that found in pulmonary alveolar proteinosis, hence the term acute silicoproteinosis.The chest radiograph demonstrates widespread alveolar opacity with an upper and mid zone dominance. Air

PATTERNS OF DISEASE CAUSED BY SILICA

Clinical pattern

Duration and level of exposure

Acute silcoproteinosis

Occurs in response to a massive inhalation of silica (e.g. in sandblasting) usually within a few weeks to 4–5 years after exposure

Accelerated silicosis

Develops less than 10 years after first inhalation of high concentrations of silica. Its more rapid development than in simple silicosis indicates that the worker is at great risk for the development of progressive massive fibrosis

Chronic simple silicosis

The most common manifestation usually developing after 10–50 years of low level silica exposure

Figure 19.30 Progressive massive fibrosis in coalworker’s pneumoconiosis. Mass-like opacities are seen bilaterally in the upper lobes in association with multiple small nodules and calcified mediastinal lymphadenopathy.

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bronchograms may be seen initially and hilar and mediastinal adenopathy also occur. Studies have shown that silica workers have an increased risk of IPF154,155, although epidemiological data are currently insufficient firmly to establish an aetiological link between exposure to silica and IPF-like diseases156. In addition, there has been a long-recognized association of silicosis with connective tissue disease (CTD)157. Among the CTDs, the association of silicosis and rheumatoid arthritis (Caplan’s syndrome) is more common than systemic sclerosis (Erasmus syndrome). In the development of CTD, it appears that exposure to very fine silica dust (silica flour) is necessary; this exposure may be experienced by dental technicians and workers exposed to fine scouring powders158.

Asbestos-related disease Asbestos is the generic term for a group of fibrous silicates that share the property of heat resistance. They are classified into two groups: the serpentines and the amphiboles.The only serpentine asbestos used commercially is chrysolite, which accounts for more than 90% of the asbestos used in the USA. The pathological hallmark of asbestos exposure is the asbestos body consisting of an asbestos fibre usually 2–5 µm in width. These bodies can be identified in tissue sections in interstitial fibrous tissue and intra-alveolar macrophages in broncho-alveolar lavage (BAL) fluid. The effects of asbestos on the lung are diverse and clinical manifestations of these abnormalities typically do not appear until 20 years or more after initial exposure, apart from asbestos-related pleural effusions which may be present as early as 5 years post exposure.

Benign pleural effusions The exact prevalence of benign pleural effusions is unknown, as many are subclinical. The effusions are typically haemorrhagic exudates of mixed cellularity and usually do not contain asbestos bodies. Their diagnosis is therefore reliant largely on the exclusion of other causes of effusions in an asbestos-exposed patient.The development of effusions is thought to be exposure dependent159.The effusions are often small, may be persistent or recurrent and may be simultaneously or sequentially bilateral160. Diffuse pleural thickening is the usual consequence.

Pleural plaques The most common manifestation of asbestos exposure is pleural plaques which macroscopically are discrete foci of pearly white fibrous tissue, usually 2–5-mm thick. They involve the parietal pleural almost exclusively and on the chest radiograph are classically distributed along the posterolateral chest wall between the 7th and 10th ribs, lateral chest wall between the 6th and 9th ribs, the dome of the diaphragm and the mediastinal pleura161. CT also demonstrates anterior and paravertebral plaques that are not well demonstrated on chest radiography. Calcification is reported in 10–15% of cases161. At histological examination, the plaques are relatively acellular, with a ‘basket-weave’ appearance of collagen bundles. Asbestos fibres (usually chrysolite) are often seen, but asbestos bodies are usually absent. CT is undoubtedly more sensitive for the detection of pleural plaques. Only

50–80% of cases of documented pleural thickening are detected by chest radiography162,163; on chest radiography pleural plaques were most commonly missed in the paravertebral and posterior regions of the costal pleural164. Studies have suggested that pleural plaques are not associated with significantly impaired lung function165,166.

Diffuse pleural thickening The frequency of diffuse pleural thickening increases with time from first exposure and is thought to be dose related. It results from thickening and fibrosis of the visceral pleura, which leads to fusion with the parietal pleura and may be caused by extension of interstitial fibrosis to the visceral pleura, consistent with the pleural migration of asbestos fibres. Diffuse pleural thickening superimposed on circumscribed plaques has been observed, often after a pleural effusion. Histologically, there is a similarity between pleural thickening and plaques, except that fusion of the pleural layers is suggestive of more intense inflammation. It has been shown that workers with diffuse pleural thickening have a significant reduction in forced vital capacity (FVC) and gas transfer (DLCO)167. CT is more sensitive and specific than chest radiography in the detection of diffuse pleural thickening168 and is better at the distinction between mild pleural disease and extrapleural fat169. Although oblique views can enhance detection of pleural abnormalities in cases in which HRCT is unavailable, they may also fail to distinguish plaques from extrapleural fat170.

Round atelectasis Round atelectasis, also known as folded lung, is a form of parenchymal collapse that occurs most commonly in the peripheral lung in the dorsal regions of the lower lobes. Pathological examination shows pleural fibrosis overlying the abnormal parenchyma as well as invaginations of fibrotic pleura into the region of collapse. The appearance suggests that retraction of collagen in the pleura as it matures is the cause of the collapse. Because of the pathogenetic association with fibrosis, the areas of atelectasis are always seen adjacent to the visceral pleura. A characteristic finding is the presence of crowding of bronchi and blood vessels that extend from the border of the mass to the hilum (‘comet tail’ sign)171. In most cases, the collapsed lung has a rounded or oval shape; however, wedgeand irregularly-shaped masses can also occur (Fig. 19.31).Volume loss of the affected lobe is invariably present and often associated with hyperlucency of the adjacent lung172. Serial examinations show a relatively stable appearance, and the differentiation from a lung neoplasm is usually straightforward on CT.

Asbestosis Asbestosis is defined as pulmonary parenchymal fibrosis secondary to inhalation of asbestos fibres. The lag between exposure and onset of symptoms is usually 20 years or longer. Histologically, fibrosis is first seen in the interstitium of respiratory bronchioles, particularly in the lower lobes adjacent to the visceral pleura. With advancing disease, the fibrous tissue extends into the adjacent alveolar septa, eventually involving the entire lobule173. In the

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most severe cases there is diffuse interstitial fibrosis associated with parenchymal remodelling and honeycombing. Asbestos bodies are almost always identifiable microscopically in the fibrous tissue or macrophages in residual airspaces. Early CT changes indicative of asbestosis are the presence of subpleural curvilinear lines and dots, pleural-based nodular irregularities, parenchymal bands and septal lines164.The fine reticulation eventually progresses to a coarse linear pattern with honeycombing (Fig. 19.32). These abnormalities are usually most severe in the subpleural regions of the lower lobes. HRCT–pathological correlation studies have shown that subpleu-

ral dots and branching structures correspond to peribronchiolar fibrosis174. The sensitivity of HRCT over the chest radiograph for the identification of early fibrosis in asbestos-exposed individuals is well established175,176; however, sensitivity is not 100% and a histopathological diagnosis of asbestosis can be present in patients with normal or near-normal HRCTs177.The diagnosis of asbestosis has significant implications for the patient in terms of prognosis, work ability and the possibility of receiving legal compensation.Although both the chest radiograph and HRCT can confirm previous exposure, the diagnosis of asbestosis is largely inferential and based on

Figure 19.31 Atelectasis. Two examples of rounded atelectasis in association with (A) pleural thickening and (B) a pleural effusion. In both cases, there is evidence of lobar volume loss as evidenced by displacement of fissures. The most common location of rounded atelectasis is in the lower lobes.

Figure 19.32 Asbestosis. (A) HRCT features of early asbestosis include subpleural lines (arrowheads) and fine reticulation (arrows). These subtle abnormalities persisted on prone sections. (B) In more advanced disease, a coarse reticular pattern with honeycombing, often indistinguishable from usual interstitial pneumonia on HRCT, is seen. Note the calcified pleural plaques in both examples.

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demonstrating a compatible structural lesion, an appropriate exposure history with a suitable latency, and the exclusion of other plausible conditions. One of the problems in interpreting the presence of interstitial fibrosis, whether on chest radiography or HRCT, is the fact that asbestos-exposed individuals are as likely as the rest of the population to develop other causes of fibrosis such as IPF178. Distinguishing asbestosis from IPF is also desirable, as asbestosis is associated with a much slower rate of progression and hence better prognosis. Discrimination between the two by HRCT appearances is by no means straightforward and is usually impossible. It has been suggested that subpleural dot-like or branching opacities are significantly more common in patients with asbestosis, whereas honeycombing, traction bronchiectasis with areas of confluent fibrosis and a mosaic perfusion pattern resulting from air trapping are more common in patients with IPF179. Additionally, pleural disease may be a discriminator: in Akira et al’s study, pleural disease was found in 83% (66/80) of patients with asbestosis but only in 4% (3/80) of patients with IPF179. Copley et al found no statistically significant differences in the coarseness of fibrosis between individuals with asbestosis and a cohort of individuals with biopsy-proven UIP, although the CT findings of asbestosis were strikingly different from NSIP; the quality of fibrosis was coarser, there was a lower proportion of ground-glass opacification, and a higher likelihood of a basal and subpleural distribution180.

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138. Uner A H, Rozum-Slota B, Katzenstein A L 1996 Bronchiolitis obliterans-organizing pneumonia (BOOP)-like variant of Wegener’s granulomatosis. A clinicopathologic study of 16 cases. Am J Surg Pathol 20: 794–801 139. Silva C I, Müller N L, Fujimoto K et al 2005 Churg–Strauss syndrome: high resolution CT and pathologic findings. J Thorac Imaging 20: 74–80 140. Johkoh T, Müller N L, Akira M et al 2000 Eosinophilic lung diseases: diagnostic accuracy of thin-section CT in 111 patients. Radiology 216: 773–780 141. Cleverley J R, Screaton N J, Hiorns M P et al 2002 Drug-induced lung disease: high-resolution CT and histological findings. Clin Radiol 57: 292–299 142. Myers J L, Limper A H, Swensen S J 2003 Drug-induced lung disease: A pragmatic classification incorporating HRCT appearances. Semin Respir Crit Care Med 24: 445–453 143. Rossi S E, Erasmus J J, McAdams H P et al 2000 Pulmonary drug toxicity: radiologic and pathologic manifestations. RadioGraphics 20: 1245–1259 144. Ellis S J, Cleverley J R, Müller N L 2000 Drug-induced lung disease: high-resolution CT findings. Am J Roentgenol 175: 1019–1024 145. Sheehan R E, Wells A U, Milne D G et al 2000 Nitrofurantoin-induced lung disease: two cases demonstrating resolution of apparently irreversible CT abnormalities. J Thorac Imag 24: 259–261 146. Kennedy J I, Myers J L, Plumb V J et al 1987 Amiodarone pulmonary toxicity. Clinical, radiologic, and pathologic correlations. Arch Intern Med 147: 50–55 147. Vernhet H, Bousquet C, Durand G et al 2001 Reversible amiodaroneinduced lung disease: HRCT findings. Eur Radiol 11: 1697–1703 148. Goe S K, Henneberger P K, Reilly M J et al 2004 A descriptive study of work aggravated asthma. Occup Environ Med 61: 512–517 149. International Labour Office 1980 Guidelines for the use of the ILO international classification of radiographs of the pneumoconioses, revised edition. International Labour Office, Geneva 150. Hering K G, Tuengerthal S, Kraus T 2004 Standardized CT/HRCTclassification of the German Federal Republic for work and environmental related thoracic diseases. Radiologe 44: 500–511 151. American Thoracic Society Committee of the Scientific Assembly on Environmental and Occupational Health 1997 Adverse effects of crystalline silica exposure. Am J Respir Crit Care Med 155: 761–768 152. Bergin C J, Müller N L, Vedal S et al 1986 CT in silicosis: correlation with plain films and pulmonary function tests. Am J Roentgenol 146: 477–483 153. Remy-Jardin M, Beuscart R, Sault M C et al 1990 Subpleural micronodules in diffuse infiltrative lung diseases: evaluation with thinsection CT scans. Radiology 177: 133–139 154. Brichet A, Wallaert B, Gosselin B et al 1997 “Primary” diffuse interstitial fibrosis in coal miners: a new entity? Study Group on Interstitial Pathology of the Society of Thoracic Pathology of the North. Rev Mal Respir 14: 277–285 155. Honma K, Chiyotani K 1993 Diffuse interstitial fibrosis in nonasbestos pneumoconiosis—a pathological study. Respiration 60: 120–126 156. De Vuyst P, Camus P 2000 The past and present of pneumoconioses. Curr Opin Pulm Med 6: 151–156 157. Rosenman K D, Moore-Fuller M, Reilly M J 1999 Connective tissue disease and silicosis. Am J Ind Med 35: 375–381 158. Koeger A C, Lang T, Alcaix D et al 1995 Silica-associated connective tissue disease. A study of 24 cases. Medicine (Baltimore) 74: 221–237 159. Epler G R, McLoud T C, Gaensler E A 1982 Prevalence and incidence of benign asbestos pleural effusion in a working population. JAMA 247: 617–622 160. Hillerdal G 2005 Non-malignant asbestos pleural disease. Thorax 36: 669–675 161. Peacock C, Copley S J, Hansell D M 2000 Asbestos-related benign pleural disease. Clin Radiol 55: 422–432 162. Friedman A C, Fiel S B, Fisher M S et al 1988 Asbestos-related pleural disease and asbestosis: A comparison of CT and chest radiography. Am J Roentgenol 150: 269–275

163. Schwartz D A, Galvin J R, Yagla S J et al 1993 Restrictive lung function and asbestos-induced pleural fibrosis. A quantitative approach. J Clin Invest 91: 2685–2692 164. Oksa P, Suoranta H, Koskinen H et al 1994 High-resolution computed tomography in the early detection of asbestosis. Int Arch Occup Environ Health 65: 299–304 165. Van Cleemput J, De Raeve H, Verschakelen J A et al 2001 Surface of localized pleural plaques quantitated by computed tomography scanning: no relation with cumulative asbestos exposure and no effect on lung function. Am J Respir Crit Care Med 163: 705–710 166. Sette A, Neder J A, Nery L E et al 2004 Thin-section CT abnormalities and pulmonary gas exchange impairment in workers exposed to asbestos. Radiology 232: 66–74 167. Kee S T, Gamsu G, Blanc P 1996 Causes of pulmonary impairment in asbestos-exposed individuals with diffuse pleural thickening. Am J Respir Crit Care Med 154: 789–793 168. Jarad N A, Poulakis N, Pearson M C et al 1991 Assessment of asbestos induced pleural disease by computed tomography—correlation with chest radiograph and lung function. Respir Med 85: 203–208 169. Lee Y C, Runnion C K, Pang S C et al 2001 Increased body mass index is related to apparent circumscribed pleural thickening on plain chest radiographs. Am J Ind Med 39: 112–116 170. Ameille J, Brochard P, Brechot J M et al 1993 Pleural thickening: a comparison of oblique chest radiographs and high-resolution computed tomography in subjects exposed to low levels of asbestos pollution. Int Arch Occup Environ Health 64: 545–548 171. Schneider H J, Felson B, Gonzalez L L 1980 Rounded atelectasis. Am J Roentgenol 134: 225–232 172. Lynch D A, Gamsu G, Ray C S et al 1988 Asbestos-related focal lung masses: Manifestations on conventional and high-resolution CT scans. Radiology 169: 603–607 173. Craighead J E, Mossman B T 1982 The pathogenesis of asbestosassociated diseases. N Engl J Med 306: 1446–1455 174. Akira M, Yamamoto S, Yokoyama K et al 1990 Asbestosis: Highresolution CT–pathologic correlation. Radiology 176: 389–394 175. Akira M, Yokoyama K, Yamamoto S et al 1991 Early asbestosis: evaluation with high-resolution CT. Radiology 178: 409–416 176. Gamsu G 1989 High-resolution CT in the diagnosis of asbestosrelated pleuroparenchymal disease. Am J Ind Med 16: 115–117 177. Gamsu G, Salmon C J, Warnock M L et al 1995 CT quantification of interstitial fibrosis in patients with asbestosis: a comparison of two methods. Am J Roentgenol 164: 63–68 178. Gaensler E A, Jederlinic P J, Churg A 1991 Idiopathic pulmonary fibrosis in asbestos-exposed workers. Am Rev Respir Dis 144: 689–696 179. Akira M, Yamamoto Y, Inoue Y et al 2003 High-resolution CT of asbestosis and idiopathic pulmonary fibrosis. Am J Roentgenol 181: 163–169 180. Copley S, Wells A, Sivakumaran P et al 2003 Asbestosis and idiopathic pulmonary fibrosis: comparison of thin-section CT features. Radiology 229: 731–736 181. Weiland D A, Lynch D A, Jensen S P et al 2003 Thin-section CT findings in flock worker’s lung, a work-related interstitial lung disease. Radiology 227: 222–231 182. Akpinar-Elci M, Travis W D, Lynch D A et al 2004 Bronchiolitis obliterans syndrome in popcorn production plant workers. Eur Respir J 24: 298–302 183. Newman L S, Buschman D L, Newell J D Jr, Lynch D A 1994 Beryllium disease: assessment with CT. Radiology 190: 835–840 184. Harris K M, McConnochie K, Adams H 1993 The computed tomographic appearances in chronic berylliosis. Clin Radiol 47: 26–31 185. Akira M 1995 Uncommon pneumoconioses: CT and pathologic findings. Radiology 197: 403–409

SUGGESTED FURTHER READING

Books/book chapters Hansell D M, Armstrong P, Lynch D A, McAdams H P (eds) 2005 Basic HRCT patterns of lung disease. Drug- and radiation-induced

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Reviews/papers diseases of the lung. Idiopathic interstitial pneumonias and immunologic diseases of the lung. Miscellaneous diffuse lung diseases. In: Hansell DM (ed) Imaging of Diseases of the Chest, 4th edn. Philadelphia, Elsevier Mosby, pp 143–181, 485–533, 535–629, 631–709 Franquet T 2005 High resolution computed tomography of the lungs. In: Wells A U, Denton C P (eds) Handbook of systemic autoimmune diseases, vol 2. Elsevier BV Lynch D A, Newell J D, Lee J S (eds) 1999 Imaging of diffuse lung disease. Elsevier, Ontario Schwarz M I, King Jr T E (eds) 2003 Interstitial lung disease, 4th edn. BC Decker Inc, Ontario Webb W R, Müller N L, Naidich D P (eds) 2001 High-resolution CT of the lung, 3rd edn. Lippincott-Raven, Philadelphia

Akira M 2002 High-resolution CT in the imaging of occupational and environmental disease. Radiol Clin North Am 40: 43–59 American Thoracic Society/European Respiratory Society 2002 International Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias. Am J Respir Crit Care Med 165: 277–304 Cleverley JR, Screaton NJ, Hiorns MP et al 2002 Drug-induced lung disease: high-resolution CT and histological findings. Clin Radiol 57: 292–299 Kim J S, Lynch D A 2002 Imaging of non-malignant occupational lung disease. J Thoracic Imaging 17: 238–260 Lynch D A, Travis W D, Müller N L et al 2005 Idiopathic interstitial pneumonias: CT features. Radiology 236: 10–21 Myers J L, Limper A H, Swensen S J 2003 Drug-induced lung disease: A pragmatic classification incorporating HRCT appearances. Semin Respir Crit Care Med 24: 445–453

CHAPTER

Thoracic Trauma and Related Topics

20

John H. Reynolds

• • • • • •

Chest wall, lungs and pleura The diaphragm The mediastinum Thoracic imaging in the intensive care patient Lung transplantation Surgical treatment of emphysema

The major organs within the chest, namely the heart, lungs and major blood vessels, play a crucial role in providing oxygen to the tissues of the body and removing carbon dioxide. This occurs by means of pulmonary ventilation, gaseous exchange at the alveoli and the transport of oxygen and carbon dioxide by the cardiovascular system. Major trauma to the chest can disrupt one or more of these processes and consequently there is a range of serious and potentially life-threatening thoracic injuries, including aortic rupture, tracheal transection, haemothorax, haemopericardium and tension pneumothorax. In developed countries, trauma is the main cause of death in children and adults under 40 years of age. Approximately 20% of trauma deaths are directly related to chest trauma and of these around two-thirds occur as a result of motor vehicle accidents. Other causes of significant chest trauma include falls from a height, occupational injuries including falls and crush injuries, knife and gunshot injuries and domestic accidents. Trauma can be broadly divided into two categories, blunt and penetrating. Blunt trauma imparts kinetic energy to the body, which leads to tissue damage either by direct impact or by inducing shearing forces within body tissues. Penetrating injuries include knife and bullet wounds which, as well as damaging structures within the body, can also introduce infection1. Major chest injuries seldom occur in isolation. Commonly associated injuries include those to the head, extremities, spine, abdomen and pelvis2. Major trauma patients are managed on arrival at hospital in accordance with the Advanced Trauma Life Support (ATLS) protocol devised by the Committee on Trauma of the American College of Surgeons3. Patients are initially assessed with a primary survey that includes evaluation of the airway, breathing and circulation, followed by a

more detailed secondary survey once the immediate threats to life have been dealt with. Radiographs (antero-posterior [AP] supine) of the chest and pelvis are performed as adjuncts to the primary survey and the initial clinical and radiographic assessment may lead to further imaging. Protocols for the imaging of acutely injured patients have been undergoing a period of evolution in recent years. Although the chest radiograph remains a pivotal investigation in the rapid triage of trauma patients, computed tomography (CT) is a more accurate technique for the characterization of virtually all thoracic injuries, particularly those of the heart, pericardium, thoracic spine, mediastinum, aorta and lungs. Many trauma patients require imaging of several body areas and current multidetector CT (MDCT) systems are able to perform a whole body study in a matter of seconds. As well as allowing a detailed cross-sectional study of the trauma patient, these advanced CT machines minimize the time the patient has to spend away from the emergency department where he/ she can be cared for more safely. The quantity of image data obtained can be problematical—one solution may be to have a brief overview of the CT study at the time the patient is in the CT unit for triage purposes followed by a more detailed interrogation of the images by the radiologist once the patient has returned to the emergency unit. Concerns about the radiation dose relating to MDCT need to be kept in mind but the low threshold for the use of CT can save the patient from other radiological procedures such as radiography of the spine or catheter angiography4.

CHEST WALL, LUNGS AND PLEURA Rib fractures Rib fractures can occur in up to 50% of patients with blunt chest trauma. More than 50% of acute fractures are missed on initial radiographs owing to the superimposition of structures or because the fracture line is not tangential to the X-ray beam5. Additional lateral or oblique views to assess the ribs are inappropriate in the acute trauma patient. They are time consuming and do not alter clinical management as rib fractures

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are almost invariably treated conservatively. The main purpose of the chest radiograph is to detect complications such as pneumothorax, haemothorax, or pulmonary contusion. Rib fractures lead to local bleeding and may result in an extrapleural haematoma. This is visible on the chest radiograph or CT study as a convex soft tissue bulge projecting towards the lung (Fig. 20.1). Fractures of the 1st to 3rd ribs imply severe trauma and may be associated with vascular, brachial plexus, spinal, or tracheobronchial injury. In one series of 730 patients, vascular injuries were seen in 24% of multiple trauma patients with 1st rib fractures6. Fractures of the 10th to 12th ribs, often better seen on an abdominal radiograph, are associated with injuries to the liver, spleen, or kidneys. Further imaging of these organs is mandatory when such fractures are detected2,7. In children, rib fractures are uncommon and are usually of the greenstick variety. Rib fractures are rare in accidental injury in children and their presence should raise the possibility of nonaccidental injury, particularly if they involve the posterior aspects of the ribs7. In children, teenagers and young adults the ribs have great elasticity. Major blunt trauma in this age group may well lead to significant intrathoracic injury, such as tracheobronchial, diaphragmatic, or aortic rupture without any associated rib fracture2. Double fractures of three or more adjacent ribs, or adjacent combined rib and sternal or costochondral fractures, result in a flail segment which moves paradoxically during the respiratory cycle (Figs 20.2, 20.3). This injury, referred to as ‘flail chest’, can lead to impaired ventilation and pulmonary atelectasis. There is usually severe associated pulmonary contusion which, together with associated injuries, contributes to a high mortality (in the region of 40%)2.

Figure 20.2 Flail chest. Chest radiograph with multiple left-sided lateral and posterior rib fractures resulting in a flail chest. There is associated left lung contusion.

Figure 20.3 Flail chest. CT image of a left-sided flail chest with a segment of the chest wall pushed inwards. This is known as a ‘stove-in-chest’.