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Meningioma with Remarkable Multiple Rosette Formation: A Diagnostically Difficult Case

Kenichi Mizutani, Satoko Nakada, Akira Tamase, Osamu Tachibana, Hideaki Iizuka, Takanori Hirose and Sohsuke Yamada

Background: Rosette formation is a rare morphological feature in meningiomas. It can be seen in angiomatous, meningothelial, transitional, secretory, papillary or rhabdoid subtype; however there are very few reports of meningiomas with rosettes, and the feature itself is not criterion for the WHO grade, so this feature sometimes makes the diagnosis difficult.

Case presentation: A 62 y old Japanese woman stumbled and was admitted to a hospital. Magnetic resonance imaging showed a 50 mm extra-axial tumor on the right cerebral falx. Histologically, the tumor contained multiple rosettes that had a central nuclear-free zone without a vessel core. It also showed a sheet-like or whorled growth pattern and pseudopapillary structure. Some round tumor cells had abundantly dense eosinophilic cytoplasm, displaying rhabdoid features. High cellularity, small cells with a high nuclear-to-cytoplasmic ratio and prominent nucleoli were recognized, but the mitotic activity was less than 1/10 high-power fields. The tumor was immunohistochemically positive for EMA and synaptophysin (weakly) but negative for GFAP, progesterone, STAT6, S-100, NeuN and melan A. The Ki-67 labeling index was merely 0.5%. Although ependymoma was considered as the first differential diagnosis, it was ruled out, as perivascular pseudorosettes and ependymal rosettes were not seen. We ultimately made a diagnosis of atypical meningioma with a rosette-like and pseudopapillary pattern, WHO grade II.

Discussion and conclusion: The meningiomas in this case showed remarkable rosette formation, but as this is not criterion for deciding WHO grade, grading was diagnostically difficult. Papillary meningioma was also considered as a critical differential diagnosis; however, our final diagnosis was made after considering the very low mitotic activity and Ki-67 labeling index, which were not consistent with WHO grade III. This case was very unique and diagnostically difficult. This report may be an aid for the diagnosis of pathologically unusual entity.