Purpose: To describe the magnetic resonance imaging and histopathologic features of an orbital granular cell tumor.
Methods: A 43-year-old man was initially examined with slowly progressive vertical diplopia. A firm mass was palpable through the left lower eyelid. Magnetic resonance imaging and histopathologic examinations were performed.
Results: Magnetic resonance imaging disclosed a spindle-shaped mass involving the inferior oblique muscle. Histopathologic examination disclosed that the tumor cells, diagnosed as a granular cell tumor, had infiltrated the muscle fibers.
Conclusion: In the present case, these findings indicate that the granular cell tumor may develop in the inferior oblique muscle.