Granular cell tumor of the eye (myoblastoma): ultrastructural and immunohistochemical studies.

The clinical and pathological characteristics of a myoblastoma of the orbital are described. The tumor presented as a painless hard mass in the left orbit of a 56-year-old caucasian male, causing diplopia and hypertrophy of the left eye in the primary visual position. Light microscopy studies revealed a typical granular cell tumor with PAS-positive intracytoplasmic granules. Immunoperoxidase studies showed positivity for S-100 protein and desmin. Electron microscopy studies showed numerous intracellular myelin degenerative bodies. The patient developed an epidermoid cyst at the site of initial surgery, but has no signs of local or distant disease two years after initial treatment.