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Onodi cell on the right is demonstrated, extending into the anterior clinoid processes. On the left a smaller Onodi cell is noted, but aeration of the left anterior clinioid process is due to a recess of the sphenoid sinus (best seen on coronal images).
Onodi cells refer to extension of the posterior-most ethmoidal air cells superolateral tot he sphenoid sinus, into the anterior clinoid processes. If they become infected, or mislead the endoscopist, they can lead to involvement of the optic canal.