409 Cellular Variant of Hemangioblastoma Presenting as an Extra-Axial Cerebellopontine Angle Lesion: A Rare Case Report

Introduction/Objective Hemangioblastomas (HBs) are rare, highly vascular neoplasms of the central nervous system, typically arising intra-axially. They constitute approximately 2.5% of all intracranial tumors and up to 12% of neoplasms in the posterior fossa. Classified as WHO Grade I, HBs generally follow a benign clinical course. Extra-axial presentation is exceedingly rare and presents a significant diagnostic challenge due to radiologic similarity to other pathologies such as dural metastases, vascular schwannomas, or meningiomas. We describe an unusual case of extra-axial hemangioblastoma with atypical histologic and immunohistochemical features, consistent with the cellular variant of HBs Methods/Case Report A 70-year-old female presented with a two-year history of progressive dizziness, confusion, and behavioral changes, with acute exacerbation over recent months. Neuroimaging revealed a 4.8 x 3.5 x 2.8 cm ill-defined, extra-axial lesion in the superior left posterior fossa, associated with significant vasogenic edema, mass effect, and non-communicating hydrocephalus. The lesion appeared radiologically vascular, with a differential diagnosis including meningioma or a vascular neoplasm. Histopathologic analysis demonstrated neoplastic cells with round to oval nuclei, mild to moderate nuclear atypia, prominent vascularity, and focal cytoplasmic vacuolation. No necrosis or increased mitotic activity was observed. Immunohistochemical staining showed focal positivity for inhibin, while markers including GFAP, EMA, progesterone receptor, SSTR2, STAT6, CD34, Brachyury, D2-40, BCL2, CAM5.2, and CD10 were negative. The Ki-67 proliferative index was elevated at 5–7%. Despite the extra-axial location and limited inhibin expression, the findings supported a diagnosis of the cellular variant of hemangioblastoma. Methylation profiling via ISCAB CNS tumor classifier confirmed the diagnosis of hemangioblastoma. This variant is known to demonstrate a higher proliferative index compared to the classic or reticular subtypes, potentially indicating a more aggressive biological behavior and increased risk of recurrence. Results N/A Conclusion Extra-axial hemangioblastomas of the cellular variant are exceedingly rare. Recognition of this entity is critical, particularly in atypical locations with non-classical immunoprofiles. Features such an elevated Ki-67 index may suggest a higher risk for aggressive behavior and recurrence, underscoring the importance of accurate diagnosis for appropriate clinical management