[Cerebral hemangiopericytoma. Ultrastructural study of one case].

The authors report electron-microscopic observations upon a primitive cerebral haemangiopericytoma. The vascular appearance of the tumour is due to the presence of abundant extracellular material which has a structure like that of vascular basement membranes. The fact that the tumour cells are pericytes is confirmed by the existence of intracytoplasmic microfilaments of 60-80 A in diameter, sometimes gathered into osmiophilic aggregations and forming simple cellular junctions (zonulae adherentes). Stress is laid upon the importance of differentiating this rare tumour from an angioblastic meningioma; the haemangiopericytoma is more rapidly growing and carries a more serious prognosis.