Ultrastructure of a hemangiopericytoma and a glomus tumor

A comparative ultrastructural study of a case of hemangiopericytoma and one of glomus tumor is presented. The study revealed the hemangiopericytoma cells to be large with large irregular nuclei. The intercellular spaces are filled with light osmiophilic material resembling basement membrane. In the glomus tumor, two types of cells are identified. The more frequent cells are epithelioid smooth muscle cells with large ovoid nuclei and cytoplasm filled with fine filaments. The second type of cell is less frequent and is recognized as a mast cell. It is suggested that the release of mast cell granules plays an important role in the contraction of epithelioid smooth muscle and therefore controls the flow of blood in the glomus structure.