Ultrastructural study of hemangiomas. 2. Benign hemangioendothelioma of the hard palate.

A case of benign hemangioendothelioma which occurred in the hard palate was observed and its electron microscopic findings were described. The endothelial cells contained an abundance of cytoplasmic filaments, but they contained a small number of Weibel-Palade bodies. Two types of endothelial cells, light and dark, were found in our specimen. The former had a cytoplasm with an abundance of ribosomes, rough endoplasmic reticulum and scant filaments. The latter had a cytoplasm with numerous cytoplasmic filaments and a well-developed Golgi apparatus. Tight junctions were seen between the endothelial cells. The majority of the pericytes were accompanied with the vessels in the tumor. Three types of pericytes were recognized: endothelial cell-like, fibroblast-like, and smooth muscle cell-like pericytes.