Orbital schwannoma originating from the superior oblique muscle.

PURPOSE: Orbital schwannoma in extraocular muscles is quite rare. In this study, we describe what, to the best of our knowledge, represents the first report of a schwannoma in the superior oblique muscle. METHODS: A case report relating clinical features as well as radiologic, surgical, and histologic findings is presented. RESULTS: A 27-year-old man presented with a 2-year history of progressive swelling in the left upper eyelid. A smooth mass was palpable within the superior nasal orbit. The left eye was slightly displaced inferiorly, and upward gaze was mildly impaired. There was no strabismus in the primary position. Magnetic resonance imaging revealed a well-defined mass in the left superior orbit measuring 32 × 18 × 8 mm, with a high T2 signal and low-to-moderate signal on T1. A left anterior orbitotomy was performed, and the tumor was completely resected. The mass originated from the tendon of the superior oblique muscle, and histologic diagnosis confirmed a schwannoma of Antoni type A. After this procedure, all symptoms were relieved and left superior oblique function was normal. No recurrence was evident at 6 months after surgery. CONCLUSIONS: This rare case demonstrates that orbital schwannoma may occur in association with the superior oblique muscle. With careful surgical dissection, normal function of the involved muscle can be restored.