Background: 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. Given the anatomical proximity of the accessory nerve to the foramen magnum, tumors in this region can be diagnostically challenging as they are rare and may mimic regular dural-based foramen magnum meningiomas. Case Description We report the case of a 66-year-old woman who presented with dizziness, headaches, and left-sided shoulder weakness. Imaging examination revealed a well-circumscribed, homogeneously enhancing extra-axial mass at the level of the foramen magnum without a dural tail or hyperostosis. The lesion was initially presumed to be a regular foramen magnum meningioma. Surgical resection was performed via a left-sided far-lateral approach. Intraoperatively, the spinal accessory nerve was centrally engulfed by the tumor, with gross invasion of the nerve sheath and no identifiable dissection plane. The standard microsurgical technique was employed by identifying the nerve’s proximal and distal ends and dissecting through the tumor under high magnification. The final histopathology confirmed the diagnosis of a World Health Organization Grade I meningioma, with strong diffuse strong somatostatin receptor 2A positivity and absence of S100 and SOX10 expressions. The patient’s postoperative recovery was uneventful, without any new neurological deficits, and follow-up magnetic resonance imaging examination at 6 months confirmed complete tumor resection without any recurrence. Conclusion: Accessory nerve meningiomas are exceedingly rare and can closely mimic the more common dural-based foramen magnum tumors. When gross invasion of the nerve sheath is encountered intraoperatively, neurosurgeons should be aware that functional preservation may still be possible with meticulous microsurgical dissection under neurophysiological monitoring.