Onodi Cell Mucocele Causing Acute Vision Loss

Abstract

In 1904 Onodi first described an anatomic variation in which a posterior ethmoid cell projected within the sphenoid bone [1]. Since that time the definition of the Onodi cell, as it has come to be known, has evolved to the most posterior eth-moid air cell that has pneumatized superior to the sphenoid sinus [2]. Among rhinology surgeons, the defining charac-teristic of an Onodi cell is that it contains the optic canal. Onodi cells have been reported to occur in approximately 7% of the general population in computed tomography (CT) studies, but in cadaveric studies they have been reported to be present in up to 60% of specimens [3]. The discrepancy may be due in part to the fact that older studies using thick section axial CT without isotropic resolution were less sen-sitive for detecting small air cells which are often flat in configuration within the plane of axial section [4]. Identifi-cation of an Onodi cell is of importance prior to sinonasal surgery due to the close anatomic relationship between this posterior air cell and the optic nerve ([5]; Fig. 1).Most often an incidental finding, the Onodi cell is rarely involved in pathologic processes. In essence any process which is typically associated with the paranasal sinuses may be found within an Onodi cell including infectious or inflammatory sinusitis, fungus ball, inverted papilloma, mucocele or sinonasal malignancy. Given the proximity of the adjacent optic nerve, lesions of the Onodi cell may pre-sent with vision changes as the process extends beyond the borders of the cell or expands the osseous margins [6].