Angiographically occult vascular malformation of the intracranial accessory nerve: case report.

Angiographically occult cerebral vascular malformations (AOVMs) are usually found in the supratentorial brain parenchyma. Uncommonly, AOVMs can be found within the cavernous sinus or basal cisterns and can be associated with cranial nerves. AOVMs involving the intracranial segment of the spinal accessory nerve have not been described. A 46-year-old female patient presented with a history of episodic frontal headaches and episodes of nausea and dizziness, as well as gait instability progressing over 6 months prior to evaluation. Imaging revealed a well-circumscribed 3-cm extraaxial T1-weighted isointense and T2-weighted hyperintense contrast-enhancing mass centered in the region of the right lateral cerebellomedullary cistern. The patient underwent resection of the lesion. Although the intraoperative appearance was suggestive of a cavernous malformation, some histological findings were atypical, leading to the final diagnosis of vascular malformation, not otherwise specified. The patient's postoperative course was uneventful with complete resolution of symptoms. To the authors' knowledge, this is the first report of an AOVM involving the intracranial portion of the accessory nerve. For any AOVM located within the cerebellomedullary cistern or one suspected of involving a cranial nerve, the authors recommend including immunohistochemistry with primary antibody to neurofilament in the histopathology workup.