CT in the diagnosis of interstitial lung disease

The computed tomographic (CT) appearance of interstitial lung disease was assessed in 23 patients with known interstitial disease. These included seven patients with fibrosing alveolitis, six with silicosis, two with hypersensitivity pneumonitis, three with lymphangitic spread of tumor, two with sarcoidosis, one with rheumatoid lung disease, and two with neurofibromatosis. The CT appearance of the interstitial changes in the different disease entities was assessed. Nodules were a prominent CT feature in silicosis, sarcoidosis, and lymphangitic spread of malignancy. Distribution of nodules and associated interlobular septal thickening provided further distinguishing features in these diseases. Reticular densities were the predominant CT change in fibrosing alveolitis, rheumatoid lung disease, and extrinsic allergic alveolitis. A marked peripheral predominance of the interstitial densities was seen in all seven cases of fibrosing alveolitis and in the patient with rheumatoid lung, in marked contrast with the two cases of hypersensitivity pneumonitis in whom a central distribution of the changes was seen. The observed patterns correlate with the pathologic findings and provide information that at times cannot be obtained from the chest radiograph. CT can be useful in the investigation of selected instances of interstitial pulmonary disease.