Meningeal Hemangiopericytomas and Meningomas: a Comparative Immunohistochemical and Genetic Study

Background: The meningeal hemangiopericytoma (MHPC) is a vascular tumor arising from pericytes. Mostintracranial MHPCs resemble meningiomas (MNGs) in their clinical presentation and histological featuresand may therefore be misdiagnosed, despite important differences in prognosis. Materials and
Methods:We report 8 cases of MHPC and 5 cases of MNG collected from 2007 to 2011 from the Neuro-Surgery andHistopathology departments. All 13 samples were re reviewed by two independent pathologists and investigated byimmunohistochemistry (IHC) using mesenchymal, epithelial and neuro-glial markers. Additionally, we screenedall tumors for a large panel of chromosomal alterations using multiplex ligation probe amplification (MLPA).Presence of the NAB2-STAT6 fusion gene was inferred by immunohistochemical staining for STAT6.
Results:Compared with MNG, MHPCs showed strong VIM (100% of cases), CD99 (62%), bcl-2 (87%), and p16 (75%)staining but only focal positivity with EMA (33%) and NSE (37%). The p21 antibody was positive in 62% ofMHPC and less than 1% in all MNGs. MLPA data did not distinguish HPC from MNG, with PTEN loss andERBB2 gain found in both. By contrast, STAT6 nuclear staining was observed in 3 MHPC cases and was absentfrom MNG.
Conclusions: MNG and MHPC comprise a spectrum of tumors that cannot be easily differentiatedbased on histopathology. The presence of STAT6 nuclear positivity may however be a useful diagnostic marker.