Protrusion of the optic nerve into the ethmoid and sphenoid sinus: prospective study of 150 CT studies.

Damage to the optic nerve is a serious complication of intranasal sinus surgery. Protrusion of the optic canal into the sphenoid sinus is a major risk factor. In this prospective study of 150 CT studies, we found this anatomical variation in 8% of cases. It was consistently associated with pneumatisation of the ipsilateral anterior or clinoid process. Protrusion of the optic nerve into the posterior ethmoid cells was never observed. CT is a useful part of the preoperative investigation of patients undergoing intranasal sinus surgery. Axial and coronal images obtained or by direct acquisition by reconstructions are necessary to show the position of the optic nerve.