Granular cell tumor of the orbit.

An 18-year-old woman had a 3-month history of increasing proptosis and visual loss secondary to an inferior orbital mass. Surgical exploration revealed an encapsulated mass in the orbit. After this mass was excised good vision was restored. The diagnosis of granular cell tumor was made as a result of various microscopic studies. The location of the tumor within the orbit is unusual and its histologic origin is uncertain. Immunohistochemistry by peroxidase-antiperoxidase method revealed that this tumor had S-100-protein-positive cells and negative results for lysozyme and alpha-1-antitrypsin. This fact suggests that the origin of the granular cell tumor may be due to the Schwann cell.