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.
Frontal
Maxillary
Ethmoid
Sphenoid