Mucocele in an Onodi cell responsible for acute optic neuropathy.

An Onodi cell is defined as the most posterior ethmoid cell, which pneumatizes laterally and superiorly to the sphenoid sinus. A rare case of an isolated mucocele in an Onodi cell with unilateral acute visual disturbance is presented. MRI was imperative for the early and accurate diagnosis, and prompt surgical drainage resulted in dramatic visual recovery.