An Ectopic Tentorial Schwannoma Mimicking Tentorial Meningioma: A Case Report and Literature Review.

Intracranial schwannomas account for approximately 8% of all primary brain tumors, and the majority arise in the cerebellopontine angle. Ectopic schwannomas that originate from non-cranial nerve sites, such as the dura mater or brain parenchyma, are rare, representing less than 1% of all intracranial schwannomas. These lesions often mimic meningiomas on neuroimaging, making preoperative diagnosis challenging. A woman in her 50s was referred to our department after a brain check-up incidentally revealed a mass lesion extending both above and below the tentorium. Neurological examination was unremarkable. Magnetic resonance imaging demonstrated a well-defined, heterogeneously enhancing extra-axial mass widely attached to the tentorium, suggestive of meningioma. The lesion was completely resected via a suboccipital approach. Histopathological examination revealed spindle-shaped tumor cells with palisading nuclei, positive for S-100 protein and negative for epithelial membrane antigen, confirming the diagnosis of schwannoma. The MIB-1 (Ki-67) labeling index was below 5%, consistent with a benign lesion. Postoperative magnetic resonance imaging confirmed total resection, and the patient's postoperative course was uneventful. No recurrence was observed during a 7-month follow-up period. Tentorial ectopic schwannoma is an extremely rare entity that can closely resemble meningioma both radiologically and intraoperatively. Awareness of this entity is important when evaluating tentorial extra-axial tumors. Although the clinical course is generally favorable following complete resection, careful preoperative evaluation is essential for accurate diagnosis and appropriate management.