Ultrastructure of alveoli in diffuse alveolitis

Biopsies embedded in plastic from 20 patients with dyspnea, hypoxemia and diffuse infiltration who were subjected to a diagnostic algorithm were studied on 1 μm sections by light microscopy and by electron microscopy to gain insight into the imflammatory process in the lung. Proliferation of large cubodial pleomorphic type II alveolar cells predominated in 18 patients, irrespective of the degree of fibroblastic proliferation, but were absent from areas of dense collagen. Lamellar bodies were large, numerous and often contiguous. Numerous pigment laden macrophages were the second most common feature and obstructed some alveoli. Three patients had extensive broncholization of alveoli with ciliated and goblet cells lining most alveoli; it was neoplastic in one. In 4 patients who had tissue from autopsy to compare to biopsies after 3 to 13 months, alveolar cell hyperplasia persisted but the pathology had changed. In 2, areas of necrosis surrounded by fibrosis apparently secondary to obstructed vessels, had appeared in the interval. In another, lamellar bodies of large alveolar cells were replaced by mitochondria which packed the cells, and the last showed debris filled alveoli and new interstitial fibrosis. Development of a new rapid embedding technique using DMP 30 made possible same day analysis of biopsies by light and electron microscopy. Because artifacts due to lipid extraction are avoided, it may further enhance the resolution gained by thin 1 μm plastic embedded sections. Alveolar cell hyperplasia appears to accompany inflammatory processes which culminate in necrosis or fibrosis.