Trigeminal Schwannoma Originating Motor Branch of the Trigeminal Nerve

Trigeminal schwannoma is a relatively rare intracranial tumor. Most cases present sensory changes as the main symptom and originate from the sensory branch. Therefore, the scope of influence may vary depending on the origin nerve. On the other hand, cases originating from the motor branch are very rare. The author would like to share our experience with Trigeminal schwannoma originating motor branch of the trigeminal nerve.

A 42-year-old male patient visited the neurosurgery outpatient department with gait disturbance as the chief complaint. He had no facial nerve palsy or facial numbness, and no hearing problems. He had no problems with the tandem gait, but he was showing symptoms of leaning to the right when he walked for a long time. In the performed MRI, a 4cm cystic mass compressing the brain stem was observed in the posterior fossa. The tumor did not involve the internal auditory canal and showed enhancement of the cystic wall. On the diffuse tensor image, it was confirmed that all nerves entering the IAC were traveling antero-medially to the tumor. The tumor did not invade the IAC or Meckel's cave. The surgery was performed via a retro-mastoid approach.

All nerves entering the IAC were identified in the surgical field, and these nerves were traveling inferior to the tumor. After rupturing the cyst and aspirating the internal fluid, dissection was performed along the margin of the tumor. The tumor's medial area had adhesion to the stem, so dissection was performed little by little. The tumor was strongly adhesion with a whitish-colored nerve running near the stem, unrelated to the trigeminal nerve. During intraoperative monitoring and stimulation, no facial nerve response was seen. Dissection was performed as it was thought to be an original tumor, but the nerve was completely buried in the tumor and could not be preserved, so it was sacrificed.

The tumor was able to do a gross total resection. Post-operative MRI confirmed that all tumors had been removed. After surgery, the patient had no facial palsy or hearing problems. Facial sensation was no different from before surgery and there were no symptoms. However, the tone of the masticator muscle on the right side, which was not present before surgery, decreased, masticatory function decreased, and malocclusion occurred. In response to this, rehabilitation treatment including electrical stimulation therapy was performed to restore the masticatory muscles.

Trigeminal schwannoma is a rare tumor. Among them, cases originating from the motor branch are even rarer. When a tumor suspected to be schwannoma is identified in the posterior fossa, it is necessary to carefully observe not only facial nerve palsy but also mastication function before and after surgery.

Publication History

Article published online:
07 February 2025