The immunophenotypic spectrum of meningeal hemangiopericytoma: a comparison with fibrous meningioma and solitary fibrous tumor of meninges.

Despite controversy regarding its histogenesis, meningeal hemangiopericytoma (HPC) is a well-defined clinicopathologic entity exhibiting high rates of recurrence and late extracranial metastasis. It must be distinguished from several benign neoplasms, particularly fibrous meningioma (FM) and solitary fibrous tumor (SFT). To determine the immunoprofile of HPC, we studied 27 meningeal examples, including 13 low-grade and 14 high-grade tumors. For comparison, 20 FMs and eight SFTs of the meninges were also evaluated. The immunotype of HPC included vimentin (85%), factor XIIIa (78%) in individual scattered cells, Leu-7 (70%), and CD34 (33%) in a weak, patchy pattern. Focal desmin and cytokeratin positivity was only occasionally encountered (20% each). The SFT shared a similar immunophenotype, except that CD34 expression (100%) was characteristically strong and diffuse. The FM characteristically expressed epithelial membrane antibody (EMA) (80%) and S-100 protein (80%); CD34 reactivity (60%) was patchy and weak. Both within and among all three tumor types, MIB-1 labeling indices varied widely. Specifically, they were unrelated to tumor grade in HPC. Significant reactivity for p53 protein was detected in 52% of HPCs, 17% of SFTs, and 5% of FMs. Meningeal HPC exhibits a distinct antigenic profile, one enabling the exclusion of other entities in nearly all cases. The rare expression of desmin or cytokeratin in HPC suggests either the occurrence of divergent differentiation or, less likely, the possibility that its distinctive morphology is but a phenotype shared by several types of meningeal sarcoma.