Solitary fibrous tumor of the posterior fossa: a rare and atypical case report.

Introduction: Solitary fibrous tumor (SFT) is an uncommon mesenchymal neoplasm of fibroblastic origin. Intracranial SFTs account for less than 1% of primary central nervous system tumors, and posterior fossa location is exceptional. Although often slow-growing and histologically bland, intracranial SFTs have an intermediate biological potential due to delayed recurrence and extracranial metastases. We report a posterior fossa SFT mimicking a common extra-axial lesion. Case presentation: A 60-year-old woman presented with a 1-year history of progressive headaches, vomiting, and right-sided weakness. Examination revealed right hemiparesis, cerebellar dysfunction, and central facial palsy. MRI showed a large right posterior fossa extra-axial mass compressing the fourth ventricle and causing obstructive hydrocephalus. She underwent a posterior suboccipital craniectomy with gross total resection. Histology showed patternless spindle-cell proliferation with staghorn vessels and collagenous stroma. Immunohistochemistry was positive for CD34, STAT6, and vimentin and negative for EMA, S-100, and GFAP, confirming SFT. Postoperatively, she developed hydrocephalus requiring ventriculoperitoneal shunting (Clavien-Dindo grade IIIb). At 3 months, her neurological status improved, and MRI showed no recurrence. Discussion: This case highlights the diagnostic difficulty of a posterior fossa SFT, which may mimic a meningioma or other extra-axial tumors. Atypical features included a rare infratentorial location, obstructive hydrocephalus, and postoperative cerebrospinal fluid diversion despite complete resection. STAT6 immunostaining remains central, especially where molecular testing is unavailable. Conclusion: Posterior fossa SFT is rare, characterized by benign-appearing histology yet unpredictable behavior. Complete resection, immunohistochemical confirmation, hydrocephalus management, and long-term radiological surveillance are essential.