Surgical and Radiological Differences in Intersphenoid Sinus Septation and the Prevalence of Onodi Cells with the Endoscopic Endonasal Transsphenoidal Approach

Background and Objectives: Understanding the anatomical variation in the sphenoid sinus is important to fully expose the sellar floor and clivus. Materials and Methods: The Onodi cell and intersphenoid sinus septation based on preoperative paranasal sinus computed tomography (PNS CT) and the surgical records of 877 patients who underwent the endoscopic endonasal transsphenoidal approach (EETSA) were retrospectively reviewed. Results: An intersphenoid sinus septum (ISS) blocking the clivus was defined as a pseudoclivus. Complete and incomplete pseudoclivuses were found in 2.97% and 10.5% of patients, respectively. Intraoperative and PNS CT ISS findings differed in 17.1% of patients. Misconceptions regarding a ridge or vertical ISS and confusion between an incomplete pseudoclivus and a vertical ISS were common. Conclusions: Because intraoperative and PNS CT findings may differ, anatomical variation in the paraclival area should be evaluated carefully. A pseudoclivus mimicking the clivus is important to attain a fully exposed EETSA surgical view.