Malignant granular cell tumor of the posterior orbit

Malignant granular cell tumors are rare; to the authors' knowledge, fewer than 30 cases have been reported. The histological origin of these tumors is presumed to be the Schwann cell, based on cytological and immunohistochemical similarities. The authors report a case of malignant granular cell tumor arising near the orbital apex. Clinically, the tumor originated within the confines of the third nerve, providing strong evidence for Schwann cell origin. Immunohistochemistry corroborates a Schwann cell origin. The patient had regression of this tumor after radiation therapy, emphasizing the potential usefulness of this treatment for these rare tumors.