Mulu, Abay(Ass. Prof. in Anatomy)Kinfe, Tizita2020-03-182023-11-292020-03-182023-11-292019-04http://etd.aau.edu.et/handle/123456789/21182Background:- Sphenoid sinus is an important structure localized in the body of the sphenoid bone. The sphenoid bone composes of the body, the lesser and greater wings and the pterygoid plates. The sinus is formed in the body of the sphenoid bone between the anterior and middle cranial fossa and it is surrounded by more vital structures than any other sinus. Aim:-This prospective observational study aims to determine and report the anatomical variations of sphenoid sinus by using CT scan examination. Materials and Methods:-the retrospective observational study was conducted in the Department of Radiology, Tikur Anbesa Teaching Hospital and it considers 200 subjects from age group 18 up to 79 years. Descriptive analysis was used to determine the mean, frequency and proportion of variables describing variations. 95% Confidence Interval for the proportions was presented and Chi square test was used to calculate the p-value; and p-value < 0.05 is considered significant. Result: - One hundred and seventeen (58.5%) were females with the mean age (±SD) 43 (±14.5) years. Conchal type of pneumatization was seen in 2%, presellar 25.5%, sellar 50% and 22.5% postsellar pneumatization. Single complete septa is seen in 77.5%, single incomplete in 11.5%, double septa is found in 10% and no septa is found in 1% of the cases. Conclusion:- Sellar type of pneumatization is the commonest type of pneumatization seen in the study population and single complete septa is commonest type of septum that separate the si nus in to right and left halves.en-USSphenoid Sinus, Computed Tomography, Septum, Pneumatization, Dehiscence, Protrusion.Thesis