Tumors of Pericytes
It now is recognized that a hemangiopericytic vascular pattern characterized by irregularly shaped, dilated, thin-walled blood vessels is a nonspecific finding in a wide range of neoplasms. Most tumors previously diagnosed as hemangiopericytomas are categorized as specific entities, such as synovial sarcoma, and many CD34-positive examples are interpreted as solitary fibrous tumors.
Pericytes form a single layer of cells around some capillary vessels and can manifest glomus-like or smooth muscle–like (myopericytomatous) features. True tumors of pericytes are uncommon and include myopericytomas and glomangiopericytomas. There is overlap with myofibroma. In such cases, the hemangiopericytomatous vascular pattern remains an adventitious phenomenon rather than being a specific lineage-related feature.