Mucocele and Ranula

The development of mucoceles and ranulas depend on the disruption of the flow of saliva from the secretory apparatus of the salivary glands. The lesions are most often associated with mucus extravasation into the adjacent soft tissues caused by a traumatic ductal insult; such insults include a crush-type injury and/or severance of the excretory duct of the minor salivary gland. The disruption of the excretory duct results in extravasation of mucus from the gland into the surrounding soft tissue. The rupture of an acinar structure caused by hypertension from the ductal obstruction is another possible mechanism for the development of such lesions. Furthermore, trauma that results in damage to the glandular parenchymal cells in the salivary gland lobules is another potential mechanism. ^[1]

Regarding superficial mucoceles, trauma does not always appear to play an important role in the pathogenesis. In many cases, mucosal inflammation that involves the minor gland duct results in blockage, dilatation, and rupture of the duct with subepithelial spillage of fluid. Changes in minor salivary gland function and composition of the saliva may contribute to their development. In some cases, an immunological reaction may be the cause.

Studies have revealed increased levels of matrix metalloproteins, tumor necrosis factor-alpha, type IV collagenase, and plasminogen activators in mucoceles compared with that of whole saliva. ^[2] These factors are further hypothesized to enhance the accumulation of proteolytic enzymes that are responsible for the invasive character of extravasated mucus. ^[3]

Besides ductal disruption, partial or total excretory duct obstruction is involved in the pathogenesis of ranulas in some instances. The duct may become occluded by a sialolith, congenital malformation, stenosis, periductal fibrosis, periductal scarring due to prior trauma, excretory duct agenesis, or even a tumor. Although most oral ranulas originate from the secretions of the sublingual gland, they may develop from the secretions of the submandibular gland duct or the minor salivary glands on the floor of the mouth. The mucus extravasation of the sublingual gland almost exclusively causes cervical ranulas. The mucus escapes through openings or dehiscence in the underlying mylohyoid muscle.

Occasionally, ectopic sublingual glands may be responsible for the problem. When mucus secretions escape into the neck through the mylohyoid muscle, they extend into the fascial tissue planes and cause a diffuse swelling of the lateral or submental region of the neck. The continuous secretions from the sublingual gland allow for relatively rapid accumulation of mucus in the neck and a constantly expanding cervical mass. Unlike the submandibular gland, the sublingual gland is defined as a spontaneous secretor, capable of producing secretions without neural stimulation. Inflammatory reaction to these secretions results in the formation of granulation tissue and subsequent fibrosis that may result is the entrapment of the fluid and the sealing of the leak.

The mucus retention cyst may also develop because of ductal obstruction; however, many of these lesions actually represent a distinct cystic entity of unknown cause. When ductal occlusion is involved, it is usually caused by a sialolith or an inspissated secretion that results in ductal dilatation and focal containment of the mucoid material.

The most frequently injured glands are the minor salivary glands of the lower lip. The mechanism of injury is mechanical, with the tissue of the lower lip becoming caught between the maxillary anterior teeth and the mandibular anterior teeth during mastication or with the habit of biting one's lip. This trauma results in a crush-type injury and severance of the excretory duct of the minor salivary gland. In the palate, low-grade chronic irritation (eg, from heat and noxious tobacco products) may cause these lesions to develop.

Mucoceles occur when injury to the minor salivary glands occurs usually secondary to trauma; biting one's lip; chronic inflammation with periductal scarring; excretory duct fibrosis; prior surgery; trauma from oral intubation; or rarely, minor salivary gland sialolithiasis. Most mucoceles occur because of severance of the excretory duct and extravasation of mucus into the adjacent tissue.

Birth trauma that affects the oral cavity is believed to cause some congenital mucoceles in some newborns. Potential causes include the baby sucking his or her fingers in utero or the baby passing through the birth canal. Other causes include the use of forceps during delivery or suctioning of the baby's mouth after birth.

Most ranulas are the result of escaped mucus from an injured excretory duct, while ductal obstruction of primarily the sublingual gland and rarely the submandibular gland is a less common cause. This obstruction is often due to a sialolith or mucus plug; however, chronic inflammation or infection with periductal scarring, trauma, ductal stenosis, ductal hypoplasia or agenesis, and neoplasia are other causes of ranula formation.

Anatomic variation of ductal system of the sublingual gland may increase the risk for the development of a ranula. In particular, this risk appears to be increased when the Bartholin duct is connected to and empties into the Wharton duct. ^[4]

Isolated case reports have identified Sjögren syndrome and sarcoidosis as contributing to the development of these reactive lesions. In addition, HIV infection may increase the risk of developing a ranula in children and adults. ^{[5, 6]}

Cervical ranulas are usually associated with a discontinuity of the mylohyoid muscle. The mylohyoid muscle is regarded as the diaphragm of the floor of the mouth; however, it is not a strict anatomical barrier from entry into the neck. A dehiscence or hiatus in the mylohyoid muscle has been noted in 36-45% of individuals in cadaver studies. This defect is observed along the lateral aspect of the anterior two thirds of the muscle. Projections of sublingual glandular tissue or ectopic glandular tissue may also extend into the neck; these projections facilitate cervical ranula formation. Approximately 45% of plunging ranulas occur after surgery to remove oral ranulas.

An obstruction of the excretory duct, with pooling and dilatation of the affected duct, causes the mucus retention cyst. A mucus plug appears to be the cause in most instances, although a sialolith accounts for some of these cysts.

With superficial mucoceles, mucosal inflammation, salivary gland hypofunction, and the salivary composition of the minor glands, rather than trauma, induces these lesions.

Lichen planus, lichenoid drug reaction, and chronic graft versus host disease can trigger the formation of superficial mucoceles. These transient vesicles are also a complication of head and neck radiotherapy for oral and oropharyngeal squamous cell carcinoma. ^[7]

Tartar-control toothpaste may be the inciting factor in a few cases of superficial mucoceles.

Frequency

United States

In the Minnesota Oral Prevalence Study that included 23,616 white adults older than age 35 years, mucoceles represented the 17th most common oral mucosal lesion, with a prevalence of 2.4 cases per 1000 people. Data from the Third National Health and Nutrition Examination Survey (NHANES III) that included 17,235 adults aged 17 years or older documented an overall prevalence ranking of 44 for the mucocele and a point prevalence of 0.02%. In the same study, which consisted of 10,030 children aged 2-17 years, the mucocele had a point prevalence of 0.04%. Congenital mucoceles in newborns are rare, with sporadic case reports and small case series appearing in the literature ^{[8, 9]}

Mucoceles of the anterior lingual salivary glands (glands of Blandin and Nuhn) are relatively uncommon. In the Minnesota Oral Disease Prevalence Study, Blandin and Nuhn mucoceles had a lower prevalence than mucoceles at other locations, or 0.1 cases per 1000 persons. This type of mucocele represents an estimated 2-10% of all mucoceles.

Superficial mucoceles are typically located in the soft palate, the retromolar region, and the posterior buccal mucosa. They represent approximately 6% of all mucoceles. Multiple superficial mucoceles have been reported in a small number of patients.

In an 11-year retrospective review of oral mucoceles and sialocysts from a university-based oral and maxillofacial pathology laboratory, most lesions were found to be mucus retention phenomenon (mucoceles, 91%). In descending order, the other diagnoses included ranulas (6%), and mucus retention cysts (5%). Mucoceles outnumbered mucus retention cysts by a ratio of 15.3:1.0. More limited histopathologic studies document that the mucus retention cyst (those lesions with an epithelial lining) accounts for 3-18% of all oral mucoceles.

Ranulas have a prevalence of 0.2 cases per 1000 persons and are ranked 41st in the Minnesota Oral Disease Prevalence Study. As noted previously, ranulas accounted for 6% of all oral sialocysts in a university-based oral and maxillofacial biopsy service. The prevalence of cervical (plunging) ranulas is not known; however, these lesions are considered uncommon. The number of ranulas that represents a true retention cyst ranges from less than 1% to 10%.

International

Large international population studies comparable to those undertaken in the United States are not available for oral diseases, except in Sweden. In a study of 30,000 Swedish individuals aged 15 years or older, the prevalence of mucoceles was 0.11%. ^[10] In a Brazilian study of 1200 children seen at pediatric hospital clinic, the prevalence of mucoceles was 0.08%. ^[11]

Race

No racial predilection is reported for any of the lesions.

Sex

Although no sexual predilection is usually associated with mucoceles, the prevalence of the lesions in the Minnesota Oral Disease Prevalence Study was 1.9 cases per 1000 males compared with 2.6 cases per 1000 females. Other authors have shown that mucoceles are more common in males than in females, with a male-to-female ratio of 1.3:1.

In the reported cases, superficial mucoceles and mucoceles of Blandin and Nuhn have a predilection for females.

The sexual predilection for oral ranulas slightly favors females, with a male-to-female ratio of 1:1.4, while cervical ranulas have a predilection for males. ^[12]

Age

Most mucoceles occur in young individuals, with 70% of individuals being younger than 20 years. The peak prevalence occurs in persons aged 10-20 years. Although not well studied, superficial mucoceles tend to occur in individuals older than 30 years.

Ranulas usually occur in children and young adults, with the peak frequency in the second decade. The cervical variant tends to occur a little later in the third decade.

Mucus retention cysts occur in older individuals; the peak prevalence occurs in persons aged 50-60 years.

Rarely, prenatally diagnosed and congenital mucoceles and ranulas have been reported.

Mucoceles tend to be relatively painless or asymptomatic lesions with little or no associated morbidity or mortality. Depending on the size and location, some mucoceles may interfere with normal mastication.

Oral and plunging ranulas, if large, may affect swallowing, speech, or mastication and may result in airway obstruction. The very rare thoracic ranula may compromise respiratory function and may be life threatening. ^[13]

If adequate and complete surgical excision is accomplished, the patient should expect no recurrence of mucoceles. If the adjacent minor salivary glands are not removed or are transected, the risk for recurrence increases. In the case of the anterior lingual mucocele, the offending glands of Blandin and Nuhn are deep within the musculature of the tongue and require knowledge of tongue anatomy and adequate resection to prevent recurrences. In recent pediatric studies, the recurrence rates range from approximately 6-8% following surgery. ^{[14, 15]} In a small clinical study involving children, the recurrence rates for surgical excision verus carbon dioxide laser vaporization were very similar, 5.88% and 6.67%, respectively. ^[15]

Superficial mucoceles are likely to recur periodically, and new lesions may develop over time.

Surgical therapy for oral ranulas may result in the creation of cervical ranulas. As noted previously, almost one half of cervical ranulas are those occurring after surgical attempts to eliminate oral ranulas. When these lesions are managed by marsupialization alone, the recurrence rate is high. Lesions usually develop 6-8 weeks after surgery, but recurrences may be found as late as 12 months.

With adequate surgical excision, mucus retention cysts are not likely to recur.

Educate the patient regarding early recognition of a mucocele, an oral ranula, or a cervical ranula recurrence.

If oral habits are contributing to the formation of mucoceles, it is important to eliminate the contributing factor, such as aggressive lip biting or sucking.

Educate the patient to recognize signs and symptoms of wound infection after surgical intervention and to seek the care of a dentist or physician if necessary.