Intravenous pyogenic granuloma: case report with ultrastructural findings.

A nodule, attached to the intimal surface of the external jugular vein of a 12-year-old boy, showed the light microscopic features of a pyogenic granuloma. The small muscular arteries in the adventitia contained numerous tufted intraluminal capillaries, and it is possible that the angiomatous proliferation within the jugular vein originated from the vasa vasorum, with subsequent growth into the venous lumen. This intraluminal growth dispersed the tunica elastica into the pyogenic granuloma. Ultrastructural examination showed, the lesion to be composed of capillaries lined by low and cuboidal endothelial cells, with occasional pericytes surrounded by focally multiple basal luminae. In some locations, the capillary endothelial basal lamina abutted directly on collagen with no intervening pericyte. In the stroma of the tumor there were cells with myofibroblastic features. This benign intravascular growth should be distinguished from other benign but atypical intravascular and vascular proliferations.