Ultrastructure of lung in pulmonary veno-occlusive disease

A 17-year-old boy died of severe pulmonary hypertension due to pulmonary veno-occlusive disease. The condition was diagnosed in a lung biopsy specimen and confirmed at necropsy. The lung specimen was studied by electron microscopy and immunofluorescence microscopy. The occluded pulmonary veins were lined by intact endothelial cells, beneath which was a haphazard proliferation of collagen fibrils and smooth muscle cells. The alveolar capillaries showed thickening of the endothelial cell basement membrane with an increase in the number of cytoplasmic processes of pericytes. Electron-dense deposits were located within the thickened basement membrane. These deposits were considered to represent disintegrating extravasated erythrocytes rather than immune complexes because immunofluorescence microscopy showed no immunoglobulin or complement deposition within the lung.