Fine structure of intracranial hemangiopericytoma and angiomatous meningioma

Hemangiopericytomas originate from the capillary pericyte, a cell related to a smooth muscle cell. The second tumor described is a rapidly growing intracranial vascular tumor which fits the criteria of Type IV, variant I capillary angioblastic meningioma in the Cushing and Eisenhardt classification. The evidence provided here supports the concept of a pericyte or modified smooth muscle cell as the principal cell of origin for these tumors. Detailed study of the fine structure of an intracranial hemangiopericytoma shows that this neoplasm, formerly designated as capillary ''angioblastic meningioma,'' conforms in all respects to hemangiopericytomas encountered in other organ systems. Ultrastructural features of intravascular cells in transitional type ''angioblastic meningioma'' were similar to those described for meningiomas in general. The present observations reemphasize the possibility of a histogenetic relation between intracranial hemangiopericytoma and hemangioblastoma and suggest the exclusion of both of these variants of vascular tumors from the group of meningiomas.