Electron microscopic studies on pulmonary alveolar microlithiasis.

The lung tissue of pulmonary alveolar microlithiasis was studied morphologically. Scanning electron microscopy revealed that the microliths were globular or irregular in shape or lobulated and in some loci were coalesced. The outer surface was granular or rough accompanied with deposits. The internal structures consisted of concentric laminar deposits. Frequently, two or more laminar structures were found on one cut surface. These findings may imply that the microliths grow by surface deposition and may coalesce during early stages of formation. In a high power view, granules were seen on the surface. Numerous scale-like structures and elongated electron-dense bodies inside the microliths were other peculiar findings of scanning and transmission electron microscopic studies, respectively. Elastosis in the alveolar interstitium and deposition of abundant glycogen granules in the bronchiolar epithelial cells were the notable findings of transmission electron microscopy.