Sclerosing meningioma: clinicopathological study of four cases.

Sclerosing meningioma is a distinct histologic subtype of meningioma, however, it is often confused with other tumors, especially malignant tumors. To widen our knowledge of sclerosing meningioma and to help neurosurgeons and neuropathologists diagnose this clinically and pathologically unfamiliar disease entity, we reviewed four such cases, which were originally misdiagnosed. Sclerosing meningiomas were assessed for cellularity, cellular pleomorphism, mitotic activity, brain invasion, and necrosis. Immunohistochemical staining was performed on paraffin-embedded sections using the avidin-biotin-peroxidase complex method. The histologic appearance of the underlying cerebral parenchyma invasion by tumor cells led to a diagnosis of malignant meningioma or to the completely erroneous diagnosis of ganglioglioma. The most conspicuous histologic finding of these four sclerosing meningiomas was extensive collagen deposition, so called 'sclerosis' and an intermingled small population of spindle or round cells with clear cytoplasmic halos, giving a 'fried egg' appearance. However, a typical meningothelial whorl pattern was identified in all cases. Tumor cells exhibited positive immunoreactivity for epithelial membrane antigen and vimentin, but were negative for glial fibrillary acidic protein, p53, S-100, and neuronal markers. Proliferative indices, using Ki-67, ranged from 0% to 4%, and brain invasion was present in three of four tumors. All four patients are doing well with no evidence of tumor recurrence (follow-up duration of 25 months to 12 years). Brain invasion needs to be re-evaluated as a criterion of malignancy in meningioma. Special attention should be paid to the diagnosis of this subtype of meningioma to prevent unnecessary postoperative radiotherapy and to ensure correct therapeutic decision.