Thoracic Imaging

The diffuse (interstitial) lung diseases continue to pose diagnostic and management difficulties in routine practice despite the evaluation of a large number of investigative procedures over several decades. Routine tests such as chest radiography and pulmonary function tests have limited diagnostic value and do not reliably identify patients who are more likely to respond to treatment. A cycle of initial enthusiasm with the application of a new test, followed by disenchantment, is all too familiar to respiratory physicians with an interest in diffuse lung disease. Examples that come rapidly to mind include bronchoalveolar lavage (which is occasionally highly useful, but adds little in many clinical contexts) and gallium scannning (which, despite initial reports, has no added value in diffuse lung disease, except in very occasional patients with sarcoidosis). Thus, any new test must undergo a long apprenticeship before being widely accepted as clinically useful in routine practice.

High-resolution computed tomography (HRCT) is no exception to this principle. The earliest diagnostic HRCT studies were performed in the late 1980s and were sufficiently encouraging to stimulate a prolonged evaluation of HRCT at referral centers. In time, HRCT became central to the routine evaluation of diffuse lung disease. In contrast to other tests, initial enthusiasm was sustained as experience accumulated and expertise spread to nonreferral centers. It is now clear that HRCT is the major diagnostic advance of the last 2 decades in diffuse lung disease. In the recent peer review process commissioned by the American Thoracic Society/European Respiratory Society (ATS/ERS) and the American College of Chest Physicians (ACCP), it was accepted that, in the correct clinical context, a noninvasive diagnosis of idiopathic pulmonary fibrosis (IPF) and other forms of idiopathic interstitial pneumonia is justifiable. HRCT features were a central part of noninvasive diagnostic criteria for IPF formulated by the ATS/ERS/ACCP committee. Thus, HRCT has come of age in the routine clinical evaluation of diffuse lung disease.

However, like all other tests, HRCT has flaws that should not be overlooked by the enthusiast. In this issue of Seminars in Respiratory and Critical Care Medicine, a number of those who have evaluated HRCT in the last decade and a half have produced reviews of the current role of HRCT in clinical practice. The selected topics include the diffuse lung diseases most frequently encountered by the respiratory physician, as well as disorders that pose particular diagnostic difficulty, in which HRCT may provide useful clinical insights. The issue also highlights recent technological advances. This edition captures the current application of HRCT in routine practice, stresses the advantages of HRCT, and, equally importantly, highlights its limitations.