What is a mucus retenion cyst?

Common: This is a cyst formed when a salivary or mucus gland(s) is/are blocked... Instead of the mucus draining through a natural opening, it gets trapped under the lining of the sinus or throat and creates a cyst. This are fairly common. The presence of which does not mean it needs to be removed... Only if it is causing problems.

A benign condition: It's a mucous gland which has gotten plugged and retains mucous which then expands. They can sometimes cause problems depending on how big they get, on their location, and on whether they get infected (not common). Cysts in the oral cavity are annoying and caused by biting the lip or cheek. Cysts in the sinuses are only a problem if they block a sinus opening or get so large they erode bone.