Relationship of Onodi cell to optic neuritis--radiological anatomy on coronal CT scanning

The relationship of paranasal sinusitis to optic neuritis remains controversial. One of the major sources of this controversy is that there are some reports of rhinogenic optic neuritis (RON) in patients with mild paranasal sinusitis or with almost normal paranasal sinuses. The Onodi cell is a posterior ethmoid cell which pneumatized far laterally and to some degree superiorly to the sphenoid sinus and is intimately associated with the optic nerve. Coronal CT scanning is requisite to detect the Onodi cell; when it is present, an image of the sphenoid sinus just as if it were divided into top and bottom is characteristic. In our material from 200 patients (direct coronal CT scans 10 mm in width), the Onodi cell was observed in 7%. A case of RON whose pathogenesis was considered to be a direct spread of inflammation from the localized infection of the Onodi cell is reported. Ethmoiditis localized to the Onodi cell seems to play an important role in the pathogenesis of RON. Continued careful documentation of the localized posterior paranasal sinus lesion around the optic canal by detailed diagnostic imaging and endoscopic sinus surgery is necessary to resolve the disease entity of RON.