A mucocele is a salivary gland cyst, which contains mucous content. It usually arises from the minor salivary glands. The cyst forms due to the retention of mucus within the gland, because of the rupture of the gland or obstruction of the cyst.
It is most usually found on the lower lip, but also occurs frequently on the buccal mucosa (over the cheeks) or the floor of the mouth, where it is called a ranula. Ranulas occur mostly in young adults and even more commonly in late childhood.
Its prevalence is about 2.4 per 1000 people, making it no. 15 on the list of oral mucosal conditions. They are frequently seen in younger people, usually below 20 years.
There are several variants:
- Mucus extravasation cyst: this is the most common type of mucocele and is caused by salivary gland secretion spilling out of the gland into the surrounding tissue, forming a swelling which has no epithelial capsule but is surrounded by granulation tissue
- Mucus retention cyst is due to the duct of the gland becoming blocked, and therefore has an epithelial lining. These are found in older people, between 50 and 60 years
Based on its position, a mucocele may be classified as:
- Superficial mucocele: this is located right under the mucosal surface, and occur over the age of 30 years in most cases
- Classic mucocele: this is in the upper layer of the submucosa
- Deep mucocele: this is in the lower layer of the mucous membrane
A mucocele appears as a distinct painless swelling of the mucosa, which has a fluctuant feel indicating fluid contents. It is usually less than a centimetre across, though cases in which it was several centimeters in diameter have been reported.
They appear bluish and have a translucent appearance, especially when superficial. Deep mucoceles resemble mucosal bumps and sometimes are bright red because of bleeding into the cyst. Sometimes the occurrence is preceded by recent or past trauma, or even simple biting.
Diagnosis and management
The appearance and location of the mucocele are quite characteristic, especially in the case of superficial variants. Further imaging by X-rays or ultrasound evaluation may be required depending on the suspected etiology. The fluid content makes it easy to visualize the cyst by ultrasound. Similar appearances sometimes occur with lymphangiomas or hemangiomas. Lipomas, and soft tissue abscesses, should also be ruled out.
Fine needle aspiration cytology is required to do a cell analysis as well as chemical assay. However, CT and MRI are reserved for cases when the origin or extent of the lesion is uncertain.
Surgical removal is done by excising the whole accessory salivary glands. However, large cysts are best marsupialized, or unroofed, and left open to the oral cavity, to prevent the risk of nerve injury by deep dissection or creating a deep crater. Complete excision involves removal of the accessory gland ducts and glands which could otherwise cause recurrence. In addition to surgery, laser, cryosurgery, and electrocauterization have been explored to remove mucoceles.