This case report of primary pulmonary hypertension includes descriptions of clinical, light
and, for the first time, electron microscopic features. The electron microscope revealed an
increase in thickness of the endothelial cell and basement membrane in alveolar (non-
muscular) vessels, that is, an increase in thickness of the blood/gas barrier. Pinocytic
vesicles were increased in endothelial cells of both muscular and non-muscular vessels.
Capillary lumen blockage by endothelial cells, and an onion-like lesion, recently described …