Help docs! i'm trying to find out what causes a cyst in your sphenoid sinus?

Retention cyst: Retention cysts are found often on MRI scans of the brain. These cysts are usually benign incidental findings that arise from the mucosa in the sinus. When they get large, they can cause some headache from irritation of the surrounding structures. In the abscence of a history of infection with drainage, the cause of these cysts is debated. Treatment is usually conservative.