Plexiform Schwannoma of the Spinal Accessory Nerve

Introduction: Schwannomas are benign nerve sheath tumors that infrequently develop within the jugular foramen, originating from one of the lower cranial nerves. Plexiform features are an unusual pathologic variant, reported in up to 4.3% of all schwannomas. We report a rare case of cranial nerve XI schwannoma with plexiform features.

Methods: Case report.

Results: A 38-year-old man presented with left sided tinnitus. Swallowing, phonation, vocal cord mobility, and hearing were intact. MRI identified a dumbbell-shaped, heterogeneously enhancing mass filling and expanding the left jugular foramen measuring 3.0 × 4.5 × 1.9 cm; CT showed tumor-associated bony expansion of the left jugular foramen (Fig. 1A-D). The patient underwent a left suboccipital craniotomy, which revealed a large cerebellopontine angle (CPA) lesion having the classic appearance of a schwannoma arising from XI. All CPA tumor was resected, with a small residual left extending out the jugular foramen; all cranial nerves were anatomically preserved, and all stimulated at 0.2–0.3 mA following resection—save for XI, which did not stimulate. The patient awoke at his preoperative neurologic baseline. Postoperative MRI demonstrated expected small residual tumor within the jugular foramen, and final pathology confirmed benign schwannoma with plexiform features.

Conclusion: Plexiform schwannomas are rare tumors that represent 4.3% of all schwannomas, while less than 4% of all intracranial schwannomas occur within the jugular foramen and 5.5% of these arise from XI, making a plexiform XI schwannoma exceptionally rare. These benign masses arise from sheaths surrounding nerve fascicles and are characterized by increased cellularity and nodularity, with internodular nerve segments. At present, definitive diagnosis cannot be made preoperatively, although imaging may demonstrate a hyperintense multinodular pattern with a thin, hypointense capsule wall on T2-weighted MRI. As compared with typical schwannomas, plexiform lesions may be more invested within the nerve-of-origin, potentially placing the nerve at greater risk. Correspondingly, further study aimed at defining reliable imaging characteristics would helpfully inform patient counseling and preoperative planning.