Clinical usefulness of high resolution computed tomography in cryptogenic fibrosing alveolitis.

Despite recent technological advances, agreement amongst clinicians on an algorithm for the optimal management of cryptogenic fibrosing alveolitis (CFA) has proved to be elusive. The non-invasive diagnosis of CFA is often uncertain as the clinical features may mimic those of other interstitial lung diseases. Even when the diagnosis is secure, therapeutic decisions are not straightforward. Reversible inflammatory disease requires aggressive treatment, but side eVects from an over-vigorous approach to irreversible fibrotic disease need to be avoided. The extent of disease may influence the approach to treatment, but the optimal means of staging initial severity remains contentious. Furthermore, precision in monitoring changes in disease severity at follow up is unattainable in some cases and this complicates therapeutic decisions. This review explores the impact of high resolution computed tomographic (CT) scanning on the diagnosis and management of CFA. The integration of a new test into routine management is the product of rigorous initial assessment and subsequent accumulated clinical experience. Enduring changes in clinical practice seldom result solely from “landmark” series. For example, early reports suggested that bronchoalveolar lavage (BAL) might oVer invaluable additional diagnostic and prognostic information in diVuse lung disease. 2 However, subsequent clinical experience has shown that diagnostic and prognostic trends obtained fron BAL in groups of patients are not suYciently robust to change management substantially in most cases. In the same way, although disease activity defined by 67-gallium scanning was shown to correlate with inflammatory cell content on open lung biopsy material, it transpired that 67-gallium scanning did not predict responsiveness to treatment. Initial enthusiasm generated by early studies of diagnostic tests followed by disappointment is a familiar cycle for clinicians managing patients with interstitial lung disease. Will this sequence of events apply equally to the use of CT scanning in the management of CFA? Crucially, the role of CT scanning in routine management is now validated by a decade of clinical experience and extended by technological advances. The optimal CT protocol for the evaluation of diVuse lung disease (high resolution CT scanning) was developed in the late 1980s. Important modifications included the high spatial frequency (or “bone”) reconstruction algorithm which sharpens image definition substantially by reducing image smoothing at the cost of an apparent increase in noise, and a second equally important development—reduced section thickness. It is now accepted that the best visualisation of fine detail is achieved with 1–2 mm collimation; with collimation of less than 1 mm, signal noise outweighs the benefits of fine morphological depiction. One important advantage of high resolution CT scanning is the decrease in radiation burden compared with conventional continuous section CT scanning. A standard high resolution protocol of 1.5 mm sections at 20 mm intervals from the lung apices to the bases carries a radiation dosage equivalent to 6–8 chest radiographs. Lower dose protocols may provide roughly comparable information to standard protocols in most patients but have yet to be validated clinically. Standard high resolution CT protocols have now been in place throughout the 1990s in most tertiary centres. Before the advent of CT scanning the non-invasive diagnosis of CFA was often insecure. Clinical diagnostic criteria (bilateral crackles, chest radiographic abnormalities compatible with bilateral fibrosis, lack of significant exposure to agents known to induce lung fibrosis and, in some series, a restrictive defect or isolated fall in gas transfer) were necessarily non-specific and this led some clinicians to advocate routine early open lung biopsy in patients with suspected CFA. However, others questioned whether the clinical benefit conferred by diagnostic certainty justified thoracotomy; except in tertiary institutions, the median age of patients presenting with CFA in the UK was in the seventh decade. Thus, even before CT scanning, fewer than 10% of patients with CFA in the UK had open lung biopsies in the late 1980s and early 1990s 12 compared with 50% at one tertiary institution. The precise impact of CT scanning on the non-invasive diagnosis of CFA cannot be deduced solely from the major radiological diagnostic studies of the late 1980s and early 1990s. The diagnostic sensitivity of CT scanning was evaluated in five series on a total of 501 patients with interstitial lung disease (excluding one study using inexperienced observers); in 145 patients in these five studies with a final diagnosis of fibrosing alveolitis, a correct first choice diagnosis was made in 84% on CT scanning compared with 73% on chest radiography. There are diYculties in attempting meta-analysis of these series as CT protocols (including collimation thickness) and patient characteristics diVer between institutions. However, the results are remarkably similar and, on the face of it, suggest that CT scanning enjoys a definite but inconclusive diagnostic advantage over chest radiography. It is probable that the impact of CT scanning on Thorax 1998;53:1080–1087 1080