Trochlear nerve schwannomas occurring in patients without neurofibromatosis: case report and review of the literature.

Objective and Importance: Despite their predilection for sensory nerves, intracranial schwannomas have been reported in a number of mixed and purely motor cranial nerves, especially in association with Type 2 neurofibromatosis. We report the rare occurrence of a trochlear nerve schwannoma in a patient without neurofibromatosis and review 17 other case reports from the literature.
Clinical Presentation: A 35-year-old woman presented with an 8-week history of evolving left hemiparesis, bilateral bulbar paresis, and out-of-character emotional lability.
Intervention: She underwent a left temporal craniotomy and a subtemporal, transtentorial approach to the tentorial hiatus, with complete excision of a cisternal trochlear nerve schwannoma.
Conclusion: Postoperative complications included temporary oculomotor and abducens nerve palsies and temporary right hemiparesis and mild expressive dysphasia, which were resolved at 23-month follow-up. Preoperative symptoms and signs completely resolved, but a postoperative complete trochlear nerve palsy required inferior oblique myectomy for correction of diplopia. A review of the literature showed no preoperative trochlear nerve involvement in at least 45% of cases. The tumor is isointense on T1- and T2-weighted magnetic resonance images and enhances brightly with gadolinium. The most frequently used approach for surgical excision is the subtemporal approach, and the tumor is almost always totally excised. Long-term follow-up suggests recovery of preoperative deficit, and persisting or new trochlear nerve palsy is the rule.