Surgical Technique and Nuances of Resection of a Trochlear Schwannoma: Operative Video.

Cranial nerve schwannomas accounts for around 8% of all benign intracranial tumors, arising most commonly from the vestibular nerve, followed by the trigeminal nerve and other lower cranial nerves. However, trochlear schwannoma in a patient without neurofibromatosis-2 are extremely rare and to date, fewer than 100 cases have been reported in the literature. They are either asymptomatic or present with ophthalmologic or neurologic symptoms. Diplopia is the most common initial symptom. As the tumor grows, it can compress the surrounding brainstem and other cranial nerves, causing neurologic symptoms. Asymptomatic lesions are detected incidentally following imaging for some other reason. There are no clear guidelines for the management of these tumors. In general, small asymptomatic tumors are closely observed by serial imaging and symptomatic or larger tumors are managed by surgical excision and/or stereotactic radiosurgery. Here we present a 41-year-old female patient with incidentally detected left trochlear schwannoma during the follow-up magnetic resonance imaging (MRI) scans. She was followed up regularly with multiple repeat MRI. Recently she started complaining of occasional headaches, and MRI showed a left peimesencephalic cistern tumor causing mass effect on the ipsilateral midbrain. There was also significant brainstem edema. Hence she underwent left retromastoid suboccipital craniectomy, lateral supracerbellar approach, and complete excision of the tumor. Postoperatively the patient had an uneventful recovery without any new neurologic deficits. At 6 months' follow-up the patient is doing well.