Radiology: Volume 260: Number 3-September 2011
Athol Wells, MD, FRACP
It is received wisdom that the terminal airways, often referred to as the silent zone, are the pulmonary structures most difficult to evaluate with routine noninvasive tests. However, it should now be acknowledged that with advances in the interpretation of thoracic thin-section computed tomographic (CT) results, small airways abnormalities are often easily detected by using direct or indirect thin-section CT signs (1). In interstitial lung disease, on the basis of clinical imperatives, it is increasingly clear that the pulmonary vasculature is now truly the silent zone. Pulmonary hypertension has now emerged as a major malignant prognostic determinant in advanced interstitial lung disease, irrespective of the histospecific diagnosis (2), and in some patients with less advanced disease, disproportionate pulmonary hypertension results in early mortality. This latter phenomenon is probably most frequent when there is pulmonary involvement in connective tissue disease, with disease activity occurring in separate pulmonary interstitial and vascular compartments. However, even in idiopathic pulmonary fibrosis, the paradigm of isolated progressive fibrotic lung disease, the presence of pulmonary hypertension is not reliably linked to specific measures of interstitial disease severity, including lung volumes and the extent of disease at thin-section CT (3,4). The exact prevalence of disproportionate pulmonary hypertension in mild-to-moderate idiopathic pulmonary fibrosis is now being explored in emerging data sets, but it seems that in idiopathic pulmonary fibrosis and in sarcoidosis, this lethal complication is underdiagnosed. In sarcoidosis, pulmonary hypertension, identified in approximately half of patients with chronic exercise intolerance in one sarcoidosis cohort (5), is often ascrib-able to mechanisms other than the simple ablation of the vasculature by extensive pulmonary fibrosis.
