Objective. The Onodi cell is the posterior-most ethmoid air cell and an important anatomical variant because of the intimate spatial relationship with the optic nerve, internal carotid artery, and sellar floor during sphenoid sinus surgery. The authors evaluated the incidence of Onodi cells, their clinical importance, and the association between preoperative radiological findings and surgical findings. Study Design. Case series with chart review. Setting. Tertiary care medical center. Methods. The authors retrospectively reviewed the medical records of 162 cases, including preoperative paranasal sinus computed tomography (PNS CT) findings and the findings with the endoscopic endonasal transsphenoidal approach (EETSA). They evaluated the prevalence of Onodi cells and the clinical manifestations in the patients with these cells. They also examined the clinical significance of these cells during EETSA. Results. Onodi cells were identified in the preoperative PNS CTof 53 patients, whereas Onodi cells were observed in 54 (33.3%) of the 162 patients at EETSA. The Onodi cells were bilateral in 23 patients and unilateral in 31. In all cases, the Onodi cells limited the exposure of the sellar floor. Only after removing these cells was the entire sellar floor exposed so that the tumors could be removed completely. Conclusion. Onodi cells were observed more frequently than in previous studies, and 98.1% of them were identified on preoperative PNS CT. When reviewing PNS CT images preoperatively, one needs to identify the presence of Onodi cells. The Onodi cells must be removed to completely resect tumors located in the sellar region during EETSA.
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