CT of interstitial lung disease: a diagnostic approach.

Weibel divided the pulmonary interstitium into three compartments: axial, parenchymal, and peripheral. Heitzman and others have shown that certain interstitial diseases selectively involve these compartments. A model is proposed of the CT appearances in interstitial lung disease based on Weibel's divisions. To assess the validity of this model, the distribution of disease was studied in 44 patients with proven interstitial lung disease. Lymphangitic carcinomatosis (n = 5), lymphoma (n = 2), and sarcoid in two of three patients typically involved the axial compartment. The middle (or parenchymal) compartment was abnormal in advanced stages of many interstitial diseases, particularly granulomatous diseases and drug toxicity (n = 2) in this series, but diffuse changes were seen early in extrinsic allergic alveolitis (n = 4). The peripheral compartment was predominantly affected in idiopathic pulmonary fibrosis (n = 9), rheumatoid lung (n = 3), and scleroderma (n = 1). Prominent nodularity was a feature of lymphangitic carcinomatosis and of the granulomatous diseases, silicosis and sarcoid. The presence or absence of nodules coupled with CT demonstration of differential involvement of the three interstitial compartments is useful in limiting diagnostic possibilities in interstitial disease. By more accurately showing disease distribution, a more reasonable approach to lung biopsy options may be developed.