Trigeminal nerve root entry zone pilocytic astrocytoma in an adult: a rare case of an extraparenchymal tumor.

Extra-axial cerebellopontine angle (CPA) tumors account for approximately 10% of all brain neoplasms in adults. Vestibular schwannomas are the most common, followed by meningiomas. Gliomas in the CPA are rare and quite often are the exophytic extension of primary brain stem or cerebellar tumors. We describe a pilocytic astrocytoma of the CPA that was found to arise from the proximal portion of trigeminal nerve without any anatomic continuity with the brain stem and the cerebellum. Pre-operative MRI suggested a schwannoma. The proposed origin of this extremely rare tumor is the root entry zone of the involved nerve. The tumor was completely resected via a suboccipital retrosigmoid approach.