Whorling-sclerosing meningioma. A review on the histological features of a rare tumor including an illustrative case.

Whorling-Sclerosing variant of meningioma (WSM) is a very rare variant of meningioma and only 28 cases were previously reported in the English medical literature. The term "whorling" describes different morphological features including psammoma bodies formed by precipitated calcium or by layered whorling sheets of tumor cells in meningothelial meningiomas. In WSM, the sclerosing structures are formed by typical paucicellular or acellular collagen whorls which form the majority of tumor volume. Hence, diagnosis of these tumors is based more often on morphological and histochemical features rather than on immunohistochemical findings. WSMs often contain cells with both fibroblast-like spindle cell morphology predominantly immunopositive for vimentin and meningoepithelial cells immnunopositive for EMA. The range of their Ki-67 indices differs between 0 and 4 percent. These tumors show no focal pleomorphism, necrosis and high mitotic activity. In some WSMs, entrapped GFAP immunopositive astrocytes may be seen during invasion of the adjacent neural parenchyma. Brain invasion by WSMs may give rise to erroneous diagnoses, i.e. malignant (Grade-3) meningioma, meningiosarcoma, ganglioglioma and even astrocytoma, leading detrimental overtreatment. However; hitherto, no WSM was reported exerting any aggressive behavior. Besides reviewing the literature, we also report a new WSM with abundant uncalcified paucicellular collagen whorls forming aggregates of nodules. Unlike to previous reports, this tumor was costained with p53 and progesterone receptor. The tumor showed no morphological malignancy characteristics, e.g. cellular atypia, prominent nucleoli, hypercellularity, micronecrosis/geographical necrosis, sheeting and small cells. This rare meningioma variant should be kept in mind among differential diagnoses to avoid overtreatment that might endanger patients' outcome.