Intracranial hemangiopericytoma: ultrastructural evidence of its leiomyoblastic differentiation.

Two intracranial hemangiopericytomas revealed subcellular features of the neoplastic elements comparable to those observed in normal and neoplastic smooth muscle. These included intracytoplasmic and submembranous fusiform dense bodies associated with bundles of filaments, tapered configuration of cells with grouping of cytoplasmic organelles at nuclear poles and deposition of intercellular basal lamina-like material. These observations are consistent with the pericytic origin but opposed to the ofttimes postulated meningothelial derivation of the neoplasm.