A mucocele is a benign cyst originating from a minor or accessory salivary gland, containing mucus. It is most commonly found on the lower lip, but may also occur on the ventral aspect of the tongue, the cheeks, the floor of the mouth, and the buccal mucosa.
Mucoceles are very common in the oral mucosa, with an overall prevalence of 2.4 per 1000 people. More than 70 percent of patients with mucocele are below 20 years.
The only exceptions are the ranula, which occurs above 30 years, and the retention-type mucocele, which occurs in those between 50 and 60 years.
The ranula is an oral mucocele of the sublingual gland, usually occurring in the body of the gland. Less often, it arises from the ducts of Rivini or in the parotid duct. Its appearance resembles that of a bull-frog’s throat, which has characteristic inflatable air sacs that help it to produce the croak – hence its name, from the frog, Rana tigrina. Ranulas are often larger than other oral mucoceles.
Types of Mucocele
Mucoceles may be classified as superficial, classic, or deep, depending on whether they are under the uppermost layer of the mucosa, in the upper part of the submucosa, or in the lower layers.
A mucocele may arise from extravasation or retention of mucus. The extravasation mucocele originates from traumatic rupture of the duct of a minor salivary gland, so that the salivary secretion spills out into the surrounding connective tissue stroma. This is the first stage. The mechanical trauma may result from lip biting, commonly under stress, or because of constant contact with a sharp tooth, or continuous thrusting of the tongue against the teeth.
The trauma is typically the initiatory factor except in the glands of the posterior part of the hard palate and the soft palate. There is often a discharge of viscous fluid from the swelling, following the build-up.
In the second or resorption stage, the mucus collection produces minor secondary inflammation in the soft tissue along with a swelling.
Granulation tissue appears, with inflammatory cell infiltration due to a foreign body reaction. This finally leads to the formation of a pseudocapsule.
As a result of this etiology, the extravasation cyst has no epithelialized lining, but resembles a mucus lake surrounded by granulation tissue. It is a pseudocyst in this final stage.
A retention mucocele occurs when a salivary duct is blocked, leading to the appearance of a swelling. This appears on examination as an epithelial-lined cyst of mucus.
It is less common, and is more likely to be seen on the upper lip, hard palate, floor of the mouth, and the maxillary sinus. The etiological factors include:
- duct sialoliths or stones
- duct strictures
Strictures of the duct may occur due to the chemical action by hydrogen peroxide, mouthwashes with other strong deodorant, or anti-bacterial ingredients, including anti-plaque mouthwashes, and toothpastes to control tartar build-up. These can cause recurring irritation of the oral mucosa leading to narrowing of the accessory gland ducts.