Identification of Onodi cell and new classification of sphenoid sinus for endoscopic sinus surgery.

Background: There is no effective classification method for the opening of the sphenoid sinus. The objective of this study was to examine the effectiveness of identification of the Onodi cell and classification of the sphenoid sinus using sagittal computed tomography (CT) for sphenoidotomy.

Methods: CT images of the sinuses of surgical patients (n = 261; 522 sides) were studied. Using sagittal CT, the relationships between the lateral side of the anterior wall of the sphenoid sinus and the optic nerve, and between the middle of the anterior wall of the sphenoid sinus and the skull base or pituitary gland were studied. Images were classified as demonstrating skull base (without the Onodi cell), optic canal, sella, or infra-sella (all with the Onodi cell) type.

Results: Two hundred and fifty-eight sides (49.2%) were of the skull-base type, 181 (34.7%) were of the optic-canal type, 58 (11.1%) were of the sella type, and 26 (5.0%) were of the infra-sella type; ie, the Onodi cell was present in 50.8% of sides. The width of the anterior wall of the sphenoid sinus became narrower as it shifted from the skull-base type to the infra-sella type.

Conclusions: Classification of the anterior wall of the sphenoid sinus based on the Onodi cell allows 3-dimensional assessment of the shape of the sphenoid sinus. We believe that the sphenoid sinus can be opened safely by full preoperative assessment of the anterior wall type, the position of the superior turbinate, and the position of the ostium of the sphenoid sinus.