Temporoinsular Extraventricular Neurocytoma Initially Diagnosed as Glioblastoma in a 57-Year-Old Woman: A Case Report and Literature Review.

Extraventricular neurocytoma is a rare neuronal neoplasm that may radiologically mimic high-grade glial tumors. We present the case of a 57-year-old woman with focal seizures, right-sided hemiparesis, and language impairment, whose computed tomography scan revealed a left temporoinsular mass with a cystic-necrotic component, extensive vasogenic edema, and significant mass effect, initially interpreted as glioblastoma. Subtotal resection was performed through a left frontotemporal craniotomy because of tumor adherence to the corticospinal tract. Histopathological and immunohistochemical evaluation demonstrated synaptophysin positivity, focal glial fibrillary acidic protein (GFAP) expression, a Ki-67 proliferation index of approximately 2%, and negativity for isocitrate dehydrogenase 1 (IDH1), chromogranin, and AE1/AE3, establishing the diagnosis of extraventricular neurocytoma, central nervous system (CNS) WHO grade 2. Because of residual disease, adjuvant radiotherapy followed by temozolomide was administered. At 14 months of follow-up, the patient remained free of radiological progression and demonstrated significant functional recovery. This case highlights the importance of considering extraventricular neurocytoma in the differential diagnosis of supratentorial intra-axial lesions with radiological features suggestive of high-grade glioma and underscores the value of clinicopathological and radiological correlation in establishing an accurate diagnosis and guiding treatment.