Human alveolar capillaries undergo angiogenesis in pulmonary veno-occlusive disease.

The bronchial circulation undergoes angiogenesis in several pathological conditions, such as lung neoplasm and bronchiectasis, but whether the pulmonary circulation can do this has been questioned. A woman treated with mitomycin C and 5-fluorouracil developed progressive, fatal pulmonary hypertension over 5 months. In addition to light and transmission electron microscopic examination of her lung, her pulmonary vasculature was cast and the casts were studied with scanning electron microscopy. Light microscopy showed that she had pulmonary veno-occlusive disease and angiomatoid capillary growth in the alveolar walls. Transmission electron microscopy confirmed the presence of pulmonary hypertension and showed thickened endothelial basement membrane. Scanning electron microscopy of the cast blood vessels showed distortion and destruction of alveolar capillaries prohibiting the passage of erythrocytes. Large new capillaries developed on top of, and were connected to, the shrivelled capillaries that made up the alveolar wall. The new capillaries were larger and fewer, which reduced the alveolar-capillary interface. Arteries and veins were irregularly narrowed and the veins had broad muscularity. Oedema was present, and the pulmonary lymphatics were extensively cast, especially in the lobular septa, but the lymphatics had a normal appearance. It appears that this patient suffered extensive capillary damage and venous occlusion and that the response was extensive new capillary formation, sometimes in angiomatoid configurations, and hypertrophy of pulmonary veins and arteries. Casting the microvasculature and viewing it with scanning electron microscopy identified new alveolar capillaries in this patient with acquired pulmonary hypertension.