Granular cell tumor (myoblastoma) of the orbit

A 43-year-old woman had a three-month history of increasing proptosis and visual loss secondary to an inferior orbital mass. Surgical exploration revealed an encapsulated mass that was excised with good visual recovery. Light microscopy as well as electron microscopy confirmed the diagnosis of granular cell myoblastoma. The tumor's location within the orbit was unusual and its histologic origin was uncertain.