Anaplastic meningioma versus meningeal hemangiopericytoma: immunohistochemical and genetic markers.

Anaplastic meningiomas (MIIIs) and meningeal hemangiopericytomas (HPCs) display significant morphologic and immunohistochemical overlap, including occasional cases of otherwise classic HPC with focal epithelial membrane antigen (EMA) positivity. The availability of several new biomarkers prompted us to examine the potential diagnostic roles of ancillary immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) studies. From the archival university neuropathology and consult files of 1 of the authors (A.P.), 19 meningeal HPCs and 19 MIIIs were retrieved for further study. IHC was performed by using EMA, CAM 5.2, CD99, Bcl-2, claudin-1 and Factor XIIIa (FXIIIa) antibodies. FISH was performed with NF2, 4.1B (DAL-1), chromosome 1p32, and 14q32 probes. HPCs showed strong CD99 (85% of cases), strong bcl-2 (86%), focal EMA (33%), focal claudin-1 (13%), and scattered individual cell FXIIIa (100%) positivity. MIIIs showed strong EMA (89%), strong claudin-1 (54%), weak or focal CD99 (15%), weak or focal bcl-2 (31%), and individual cell FXIIIa (84%) positivity. Focal CAM 5.2 expression was seen in 26% of HPCs and 15% of MIIIs. Deletions were extremely common in MIIIs: 1p (94%), 14q (67%), NF2 (100%), and 4.1B (67%). HPCs showed no 14q or 4.1B deletions, with 1 case each of 1p and NF2 deletions (6%). The sensitivities and specificities of the 3 most useful IHC markers (EMA, CD99, bcl-2) were 85%-89% and 67%-84%, respectively. The sensitivity and specificity of claudin-1 for MIII were 54% and 86%, respectively. The specificity and positive predictive value of combined CD99 and bcl-2 expression for the diagnosis of HPC was 95%. The sensitivities of individual genetic markers were 67%-100%, with specificities of 94%-100%. Our 3 conclusions were as follows: (1) EMA, CD99, bcl-2, and claudin-1 IHC and 1p, 14q, NF2, and 4.1B FISH are particularly useful for distinguishing anaplastic meningiomas from meningeal HPCs. (2) Focal EMA expression does not preclude a diagnosis of HPC. (3) The characteristic FXIIIa staining pattern reported for HPC also is encountered frequently in anaplastic meningiomas and therefore is nonspecific in this diagnostic setting.