A solitary hemangioblastoma located on the trochlear nerve.

Hemangioblastomas are tumors of the central nervous system that originate from the vascular system. They are most commonly composed of stromal cells in small blood vessels and usually occur in the cerebellum and spinal cord. We report a rare instance of a patient with a solitary hemangioblastoma located on the trochlear nerve. A 27-year-old woman presented with sudden onset of headache, vomiting, and diplopia. Imaging studies revealed a round mass lesion anterior to the pons with subarachnoid hemorrhage in the basal cisterns of the posterior fossa extending to the fourth ventricle. A biopsy confirmed it was a hemangioblastoma.