Epithelioid hemangioendothelioma of the gingiva: case report and ultrastructural study.

A case of epithelioid hemangioendothelioma that occurred in the mandible of a 4-year-old boy is reported, and the tumor's ultrastructural features are examined. The presence of small atypical vascular lumina, rounded or fusiform endothelial cells packed with intermediate-sized microfilaments, Weibel-Palade bodies, a small amount of distended rough endoplasmic reticulum, pinocytotic vesicles, and a basal lamina are shown. The remarkable finding of large, apparently "free" spaces within the cells that exhibit vesicle formation and sections of protrusions similar to those found in endothelial cells is discussed.