Orbital Oculomotor Nerve Schwannoma Extending to the Cavernous Sinus: A Rare Cause of Proptosis

PURPOSE To report a case of orbital oculomotor nerve schwannoma extending to the cavernous sinus through the superior orbital fissure presenting with proptosis, but without any neurological sign. CASE REPORT A 32-year-old man presented with axial proptosis of his left eye. Visual acuity and other ocular examinations were normal. Orbital magnetic resonance imaging revealed a well-defined fusiform retrobulbar lesion in the left orbit extending into the superior orbital fissure and left cavernous sinus measuring 43 mm × 21 mm × 19 mm and causing superomedial displacement of the optic nerve and axial proptosis. The patient was scheduled for surgery, and gross total excision was done. Postoperatively, the patient developed total third nerve palsy. Pre and postoperative third nerve deficit confirmed the origin of the tumor from the oculomotor nerve. Histopathological examination revealed schwannoma. CONCLUSION Orbital oculomotor nerve schwannoma, although rare, can be the cause of proptosis. Diagnosis can be confirmed histopathologically. It is a benign tumor; however, it can extend intracranially without any neurological symptoms. Therefore, neuroimaging is essential to rule out intracranial extension. Early surgical removal is mandatory.