A 36-year-old man developed acute visual loss, mimicking an optic neuritis in the left eye. Cranial magnetic resonance imaging revealed a sphenoid sinus mucocele with extension into the anterior clinoid process abutting the left optic nerve. Endoscopic marsupialization of the mucocele led to marked improvement of vision. Sphenoid sinus mucocele is discussed, as is the differential diagnosis of optic neuritis. © 2007 Elsevier Inc. All rights reserved.
