At low power, there is a cellular proliferation around abnormally formed vascular channels.

The neoplastic pericytes have round or oval nuclei and

Higher power

Meningeal hemangiopericytomas are identical to their soft tissue counterparts. These tumors arise from pericytes, which are mesenchymal cells that surround endothelial cells of capillaries and venules. Their putative role is to regulate blood flow. Pericytes are surrounded by their own basal lamina, which can be highlighted by reticulin. Pericytes possess characteristics of smooth muscle and endothelial cells (Gellman).

Histologically, pericytes form sheets and nests around vascular channels. Note that the vascular lining is composed of a single layer of nonmalignant endothelial cells. Important to differentiate from meningeal hemangiopericytomas are meningiomas with pericytomatous growth patterns. The latter will exhibit psammomatous calocospherities with tumor cells in concentric whorls as well as EMA and CD34 positivity, features absent in hemangiopericytoma (Rosai, pg 2575-7)