Schwannoma in patients with isolated unilateral trochlear nerve palsy

PURPOSE: To describe the clinical features of patients with isolated unilat eral trochlear nerve palsy secondary to imaging-defined schwannoma of the t rochlear nerve. METHODS: A chart review of all patients seen at the Neuro-Ophthalmology Uni t at Emery University since 1989, Of 221 patients with trochlear nerve pals y, six had a lesion consistent with a trochlear nerve schwannoma, RESULTS: The six patients had isolated unilateral trochlear nerve palsy. Du ration of diplopia before diagnosis averaged 6 months, Magnetic resonance i maging demonstrated circumscribed, enhancing lesions along the cisternal co urse of the trochlear nerve, all measuring less than 5 mm in greatest dimen sion. Five of the patients were seen in follow-up, over periods ranging fro m II to 26 months from initial presentation (mean, 15.6 months; standard de viation, 6.0 months). All of these patients remained stable except one, who was slightly worse at 15 months by clinical measurements and magnetic reso nance imaging, None of these patients have developed additional symptoms or signs of cranial nerve or central nervous system involvement. CONCLUSIONS: The differential diagnosis of an isolated unilateral fourth cr anial nerve palsy should include an intrinsic neoplasm of the trochlear ner ve. Magnetic resonance imaging is useful, both for diagnosis and follow-up. These patients can remain stable and may not require neurosurgical interve ntion. (Am J Ophthalmol 1999;127:183-188, (C) 1999 by Elsevier Science Inc. All rights reserved.)