Mucus retention cysts result from obstruction of salivary flow because of a sialolith, periductal scar, or impinging tumor. The retained mucin is surrounded by ductal epithelium, giving the lesion a cystlike appearance microscopically. Sialolithiasis. Obstruction due to a salivary stone, or sialolith, is usually associated with the submandibular gland. The sialolith(s) may be found anywhere in the ductal system from the gland parenchyma to the excretory duct orifice. A sialolith represents the precipitation of calcium salts (predominantly calcium carbonate and calcium phosphate) around a central nidus of cellular debris or inspissated mucin.
Clinical Features
Mucus retention cyst is less common than mucus extravasational phenomenon. It usually appears in an older age-group and is most commonly seen in the upper lip, palate, cheek, and floor of the mouth. Lesions present as asymptomatic swellings, usually without antecedent trauma. They vary in size from 3 to 10 mm and on palpation are mobile and nontender. The overlying mucosa is intact and of normal color. Mucin in floorof- mouth lesions may penetrate musculature and escape in to the soft tissues of the neck, causing a "plunging ranula."
Histopathology
Histopathology. The cystlike cavity of a mucus retention cyst is lined by normal but compressed ductal epithelial cells. The type of lining formed by the epithelial cells ranges from pseudostratified to stratified squamous. The cyst lumen contains inspissated mucin or a calcified sialolith. The connective tissue around the lesion is minimally inflamed, although the associated gland shows obstructive change.
Salivary gland neoplasms, mucus extravasation phenomenon, and benign connective tissue neoplasms should be included in a clinical differential diagnosis. Dermoid cyst might also be included for lesions in the floor of the mouth.
Treatment and Prognosis
Treatment requires removal of the mucus retention cyst and the associated minor salivary gland to avoid postoperative mucus extravasation phenomenon. Lesions of the major salivary glands can be treated in a similar way or, on occasion, only by removal of the obstruction (sialolith) if it occurs in the distal part of the ductal system. The sialolith is either surgically removed or milked through the duct orifice. If a duct is surgically entered, special precautions are used to aid the healing process so that duct scarring is minimized. Constriction of the duct through excessive scar formation could result in recurrence. Marsupialization by the placement of a silk suture in the roof of a large mucus retention cyst, particularly in one arising in the floor of the mouth, can be useful to reduce its size before surgical excision.
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