Clear cell meningioma with frequent chordoid features and aggressive behavior: a clinicopathologic study of ten cases at a single institution.

Clear cell meningioma is an uncommon variant of meningiomas that often occurs in young patients, shows a proclivity for spinal intradural extramedullary and cerebellopontine angle, and follows an aggressive clinical course. We render clinicopathologic features of ten cases of this rare tumor to further elucidate its behavior. Fifteen specimens of clear cell meningioma belonging to ten patients were obtained at a single institution from 2001 to 2009. Correlations of histologic parameters, immunohistochemical study, and clinical features were assessed. This series included eight men and two women with a mean age of 62.1 years at the first surgery. The mean post-operative follow-up period was 3.9 years. Four patients (40%) had single or multiple local tumor recurrences. The mean time to recurrence was 2.3 years. Seven tumors (46.7%) were combined with chordoid features. There was a wide range of MIB-1 labeling indices (4.4-33.5%, mean 15.8%), which were higher in recurrent tumors, tumors with chordoid features, and tumors with necrosis. There was no correlation between MIB-1 labeling indices and brain invasion. The study illustrates aggressive behavior of clear cell meningioma and frequently combined chordoid features in our cases.