Mucocele is commonly seen is sinus -

A mucocele is an epithelial lined, mucus containing sac completely filling the sinus and capable of expansion: Mucocele are most commonly formed in Frontal sinus followed by ethmoid, sphenoid and maxillary sinuses. Mucocele of frontal sinus presents as a swelling in the floor of frontal sinus above the inner (medial) canthus. It displaces the eyeball forward, downward and laterally. IOC = CT scan TOC = Endoscopic sinus surgery According to Dhingra, Least common sinus assopciated with Mucocele formation is sphenoid. But Scott Brown says: –– Most of the cases of mucocele of sphenoid sinus are referred to neurosurgeons. Therefore, it seems it is less common but actually the sinus least involved by mucocele is maxilla.