Trochlear Schwannoma Presenting as Trigeminal Neuralgia

Introduction: Schwannomas of cranial nerves controlling extraocular eye movements are extremely rare and represent a diagnostic and therapeutic challenge. We report a unique case of a trochlear schwannoma presenting symptoms of trigeminal neuralgia.

Methods: Case report.

Results: A 50-year-old previously healthy female presented with a six-month history of left-sided shock-like mandibular pain with chewing that resolved with rest, consistent with trigeminal neuralgia. She remained symptomatic despite multiple attempts at medical therapy and was subsequently referred for neurosurgical evaluation. On neurologic exam, her extraocular eye movements, corneal sensation and mastication musculature were completely intact. Repeated opening and closing of the jaw reproduced the pain, predominantly in the distributions of nerves V2 and V3. A brain MRI was performed which demonstrated a homogeneously enhancing mass in the left ambient cistern associated with the upper pons and tentorium cerebelli. No dural tail was evident, and the trochlear nerve was clearly visible entering the most posterior aspect of the tumor. The patient elected to proceed with surgical resection.

A retrosigmoid approach with cranial nerve monitoring was used to access the tumor. Intraoperatively, the mass was directly visualized arising from the fourth nerve, and stimulation of the tumor capsule had no effect. The tumor was carefully dissected away from the splayed fibers of the fourth nerve, and a gross total resection was achieved. The fifth nerve was then inspected directly, and a large indentation left by the tumor was noted at the dorsal root entry zone. A very small loop of the superior cerebellar artery was noted adjacent to the fifth nerve without direct compression, but given the patient’s clinical presentation, a microvascular decompression of the fifth nerve was performed.

Postoperatively, the patient complained of mild diplopia, but her facial pain was significantly improved, and she was discharged home in stable condition on postoperative day two. Final pathologically confirmed the diagnosis of benign schwannoma.

Conclusion: A systematic review of English-language literature revealed 31 previous cases of surgically confirmed trochlear schwannomas; four additional cases presented in other languages have been cited in previous studies. Twenty-five (81%) were located in the ambient cistern, and 15 (48%) were accessed via the subtemporal approach. To the authors’ knowledge, this is the first case of a trochlear schwannoma presenting as true trigeminal neuralgia due to compression of the trigeminal nerve. While surgical resection remains the gold standard of care for these lesions, stereotactic radiotherapy is an increasingly used and viable option for long-term tumor control.

Fig. 1