Accessory Nerve Meningioma of the Foramen Magnum: A Rare Neurosurgical Entity.

Meningiomas, which are the most common primary intracranial tumors, frequently arise from the dura of the convexities, parasagittal regions, and skull base. The accessory nerve (cranial nerve XI) at the level of the foramen magnum is an exceptionally uncommon site of origin. To date, only a few cases have been clearly documented in the literature. We report the case of a 66-year-old woman who presented with dizziness, headaches, and left-sided shoulder weakness. The lesion was initially presumed to be a regular foramen magnum meningioma. Intraoperatively, the spinal accessory nerve was centrally engulfed by the tumor, with gross invasion of the nerve sheath and no identifiable dissection plane. The final histopathology confirmed the diagnosis of a World Health Organization Grade I meningioma. Accessory nerve meningiomas are exceedingly rare and can closely mimic the more common dural-based foramen magnum tumors.