Chronic hypersensitivity pneumonitis: use of CT in diagnosis

In its subacute or chronic form, hypersensitivity pneumonitis is often difficult to distinguish clinically and physiologically from other idiopathic diffuse lung diseases. The aim of this study was to identify high-resolution CT features that allow distinction of chronic hypersensitivity pneumonitis from other chronic diffuse parenchymal lung diseases.

Six patients with chronic hypersensitivity pneumonitis were examined with pulmonary function testing, bronchoalveolar lavage, lung biopsy, chest radiography, and high-resolution CT. The chest radiographs and high-resolution CT scans were reviewed independently by three observers without knowledge of the patients' clinical status. Discrepancies between the observers were resolved by consensus.

The chest radiographs revealed normal lung volumes with a combination of abnormalities: a mixed alveolar/interstitial pattern in five cases, peribronchiolar thickening in three, a diffuse granular pattern in one, and a linear fibrotic pattern in one. In general, the high-resolution CT scans showed more abnormalities than were apparent on the plain chest radiographs. High-resolution CT revealed centrilobular, peribronchiolar, indistinct nodular opacities, of various numbers, in all cases. Four cases had areas of ground-glass density, three cases had lobular areas of hyperlucency, and one case had areas of pulmonary fibrosis and honeycombing.

We confirm that high-resolution CT can most clearly show the type and distribution of parenchymal abnormalities in patients with hypersensitivity pneumonitis. Importantly, although not pathognomonic, the high-resolution CT finding of centrilobular, peribronchiolar, indistinct nodules should suggest the diagnosis of chronic hypersensitivity pneumonitis.