Endothelial intracellular vacuoles in angiosarcoma of the scalp.

Ultrastructural observations of an angiosarcoma of the scalp revealed intracellular vacuoles both in undifferentiated and in angiomatous areas of the tumor. These structures resembled closely the 'intracytoplasmic vacuoles' described by Furusato et al. (1984); they did not appear to result from tangential sectioning through the tips of capillary loops since single endothelial cells often contained more than one intracellular vacuole. The vacuoles were separated from the cytoplasm by a membrane that was complete in some and interrupted in others. Ultrastructural examination of serial sections of endothelial cells revealed occasional tears in the septum between two adjacent intracellular vacuoles. It is suggested that a number of membrane-bound vacuoles may develop in the cytoplasm of autolytic endothelial cells and that subsequent fusion results in the production of a single intracellular vacuole.