Analysis of hemangiopericytic meningiomas by immunohistochemistry, electron microscopy and cell culture.

Intracranial hemangiopericytic meningiomas (HM) from seven patients were examined by immunostaining, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and cell culture. Positive staining for Factor VIII-related antigen was restricted to capillary endothelial cells. There was no reaction with anti-glial fibrillary acidic protein (GFAP) serum or anti-S-100 protein serum. In these neoplasms TEM displayed extracellular basement membrane-like material (BMLM), cytoplasmic intermediate filaments (IF) associated with a dense body, dilated rough-surfaced endoplasmic reticulum containing BMLM, a small area of interdigitation of cell membranes, and a unique intercellular punctate or linear density. By SEM these tumors had intercellular shell-like or reticular structures and irregularly branched capillaries which were compressed by ellipsoidal- or carrot-shaped tumor cells. Short-term monolayer culture showed rapid and vigorous growth of tumor cells, and the formation of pseudolumens but not of whorls. The TEM of cultured cells also showed cytoplasmic IF associated with the dense body. By SEM the cultured cells were flat and had a discoid nucleus with conspicuous nucleolar hillocks. Our results show that HM are mainly poorly specialized mesenchyme-related tumors of the meninges; some possess a potential for aggressive growth and some for differentiation into smooth muscle cells. Further study is needed to determine their histogenesis.