Mucus Retention Cyst is a cyst that forms when one of the mucus glands just below the vocal cord’s free margin becomes plugged. Mucus glands in this location secrete mucus in order to bathe and lubricate the vocal cords, but if a gland becomes obstructed, then the mucus it produces gets trapped and accumulates, leading to a mucus retention cyst. They typically occurs without any correlation to vocal overuse, in contrast to epidermoid cysts as well as nodules and polyps.
It can cause hoarseness, because it interferes with the normal vibrations of the vocal cords and the accuracy of their match with each other (see the videos below). The cyst is most often unilateral—that is, occurring on one cord but not the other. It appears as a bulge or deformation of the vocal cord’s free margin, and sometimes undersurface, and it may be yellowish in color.
The cyst may be surgically removed, by creating a small incision on the vocal cord and then dissecting the cyst from the cord. Photos of the surgical process can be found below. Also, the two videos below show how removing this kind of cyst can improve the voice.