Normal Variations in Sphenoid and Their Significance Regarding Endoscopic Sinus Surgeries: Multislice Computed Tomographic Study

Background:Sphenoid sinus (SS) is one of the most variables of all sinuses and its relation to vital vascular and nervous elements as optic nerve (ON), cavernous sinus, pituitary gland, and internal carotid arteries. This makes its transsphenoidal approach a challenge for functional endoscopic sinus surgeries (FESS). We aimed to delineate SS radiologically using multislice computed tomography (MSCT), to show normal variations in pneumatization pattern, septation, intercarotid distance, bony covering of carotid artery and ON, to provide successful and safe FESS -transsphenoidal surgeries and to decrease morbidity and mortality during its surgeries. Methods and materials: A prospective observational study on 210 patients from May 2017 to July 2019 was conducted and included all cases requiring MCTS, with free sphenoid sinus. We excluded patients who have pathology in SS, or previous SS surgery. Results: Onodi cells presented in 67 of cases case (31.9%) from whom 30 cases (14.3%) were bilateral, and 143 cases were absent (68.1%). Pneumatization of SS, sellar (adult) type is the most common type of pneumatization that presented in 160 cases (76.2%), presellar (juvenile) type in 48 cases (22.9%), then conchal (fetal) type only in 2 cases (0.95%). The relation between pneumatization of anterior clinoid process (ACP) and dehiscence of ON showed that among 168 cases who had absent ACP pneumatization, 159 of them showed no ON dehiscence (94.6%). Pneumatization of greater wing of sphenoid was in 28 cases (41.8%). Type I ON presented in 321 cases (76.4%), type II was in 54 (12.8%), type III was in 21 (5%), and type IV was in 24 cases (5.7%). Inter sphenoid septum was found in 119 cases (56.7%), multiple septa were found in 87 (41.4%), and no septum in 4 cases (1.9%). Dehiscence in carotid artery occurred in 17% of cases. Conclusion: We concluded SS variations, septation pattern, type of pneumatization, and onodi cells. All that will help preoperative regarding transsphenoidal surgeries, as that decrease morbidity and mortality by avoiding injury of important structures.