Schwannoma in patients with isolated unilateral trochlear nerve palsy

To describe the clinical features of patients with isolated unilateral trochlear nerve palsy secondary to imaging-defined schwannoma of the trochlear nerve.

A chart review of all patients seen at the Neuro-Ophthalmology Unit at Emory University since 1989. Of 221 patients with trochlear nerve palsy, six had a lesion consistent with a trochlear nerve schwannoma.

The six patients had isolated unilateral trochlear nerve palsy. Duration of diplopia before diagnosis averaged 6 months. Magnetic resonance imaging demonstrated circumscribed, enhancing lesions along the cisternal course of the trochlear nerve, all measuring less than 5 mm in greatest dimension. Five of the patients were seen in follow-up, over periods ranging from 11 to 26 months from initial presentation (mean, 15.6 months; standard deviation, 6.0 months). All of these patients remained stable except one, who was slightly worse at 15 months by clinical measurements and magnetic resonance imaging. None of these patients have developed additional symptoms or signs of cranial nerve or central nervous system involvement.

The differential diagnosis of an isolated unilateral fourth cranial nerve palsy should include an intrinsic neoplasm of the trochlear nerve. Magnetic resonance imaging is useful, both for diagnosis and follow-up. These patients can remain stable and may not require neurosurgical intervention.