Granular cell tumor of the inferior rectus muscle

A 53-year-old woman complaining of vertical diplopia, presented with a localized swelling in the right lower lid. Magnetic resonance imaging studies demonstrated a relatively well-defined mass in the inferior rectus with similar signal characteristics to the muscle. Excisional biopsy of the mass revealed granular cell tumor composed of S-100 positive cells with acidophilic granular cytoplasm and a peripheral lymphocytic infiltration. Granular cell tumor, which is very rare in the orbit, should be considered in the differential diagnosis of tumors adjacent to or within the extraocular muscles, particularly in the inferior orbit.