Mucoceles, exclusive of the irritation fibroma, are the most common of the benign soft tissue masses present in the oral cavity. Mucoceles (muco meaning mucus and coele meaning cavity), by definition, are cavities filled with mucus. When in the oral floor, they are called ranula (rana meaning frog and ula meaning little) because the swelling resembles the vocal or air sacs of the frog (Fig 1). Mucus is the exclusive secretory product of the accessory (minor) salivary glands and the more prominent product of the sublingual (major) salivary gland. The mechanisms for mucus cavity development are extravasation or retention. Extravasation (extra, outside; vasa, vessel) is the leakage of fluid from the ducts or acini into the surrounding tissue, while the much less common retention phenomenon occurs as a result of a narrowed ductal opening that cannot adequately accommodate the exit of saliva produced, leading to ductal dilation and surface swelling. In the case of the accessory salivary glands, the extravasation of mucus is the primary cause of mucocele formation with physical trauma as the initiating factor. The one exception is the mucous glands of the midportion of the posterior hard palate and the adjacent soft palate, where a low-grade chronic superficial irritation can lead to mucoceles of the retention variety. This is sometimes seen in cases of nicotinic stomatitis, in which irritation from heat and noxious tobacco products can result in narrowing of the ductal openings (Fig 2). The majority of retention cysts develop at the orifices of the major salivary glands. The exception is the sublingual gland: only the openings of the ducts of Rivini (5 to 15), which service the superficial portion of the gland, may develop such cysts. The pseudocystic mucoceles, regardless of their location, present as soft, painless swellings ranging from deep blue to normal pink in color. The deep blue color results from tissue cyanosis and vascular congestion associated with the stretched overlying tissue and the translucent character of the accumulated fluid beneath. The variation in color depends on the size of the lesion, its proximity to the surface, and the elasticity of the overlying tissue. The bluish color may be subtle when there is reduced elasticity of the overlying tissue or if it is somewhat distant from the surface mucosa, but it will become evident after the initial mucosal incision (Fig 3). Mucoceles of all of the accessory glands and the retention cysts of the major glands are rarely larger than 1.5 cm and they are always superficially positioned. Conversely, those arising from the deeper areas of the body of the sublingual gland are generally significantly larger and can be massive. Mucous cysts rarely present significant problems. Discomfort, interference with speech, mastication, and swallowing, and external swelling depend on size and location (Fig 4A). In cases of very large sublingual gland mucoceles, the tongue may compress the ranula to such a degree during eating and swallowing that there is interference with submandibular salivary flow. This results in obstructive symptoms and clinical enlargement of the gland (Fig 4B). This has led to diagnostic confusion in the past, when it was believed by some that the source of a ranula may be the submandibular duct. Retention cysts of Wharton’s duct occur but with a distinct clinical appearance. The lower lip is by far the most frequent site of the mucocele because it is the area most often susceptible to trauma, especially in the cuspid location (Fig 5). It is not surprising that mucoceles are rarely if ever found on the upper lip even though it has the same concentration of mucous glands. The lip is followed in frequency by the cheek and palate. On occasion, mucoceles may be seen on the ventral surface of the tongue involving the glands of Blandin-Nuhn. In most cases, this results from self-inflicted bite wounds. On even rarer occasions, the incisal gland in the anterior oral floor and the retromolar pad area may be involved. The most common origin of the ranula is the deeper areas of the body of the sublingual gland, followed to a lesser degree by the retention cysts from *Retired Clinical Professor of Oral and Maxillofacial Surgery, Columbia University, School of Dental and Oral Surgery, New York, NY. Address correspondence and reprint requests to Dr Baurmash: 4666 Hazleton Lane, Lake Worth, FL 33467; e-mail: hali2533@aol. com © 2003 American Association of Oral and Maxillofacial Surgeons 0278-2391/03/6103-0015$30.00/0 doi:10.1053/joms.2003.50074