Thứ Hai, ngày 17 tháng 5 năm 2010

Mucocele and Ranula

Introduction

Background

Collectively, the mucocele, the oral ranula, and the cervical, or plunging, ranula are clinical terms for a pseudocyst that is associated with mucus extravasation into the surrounding soft tissues. These lesions occur as the result of trauma or obstruction to the salivary gland excretory duct and spillage of mucin into the surrounding soft tissues.

Mucoceles, which are of minor salivary gland origin, are also referred to as mucus retention phenomenon and mucus escape reaction. The superficial mucocele, a special variant, has features that resemble a mucocutaneous disease. At times, the mucus retention cyst, also referred to as the sialocyst or the salivary duct cyst, is included in this group of lesions but appears to represent a separate entity on the basis of its clinical and histopathologic features. Although the mucus retention cyst is discussed in this article, its features are differentiated from the features of the pseudocysts. The lesions of the sinus, such as sinus mucoceles, pseudocysts, and retention cysts, are not included in this discussion.

Ranulas are mucoceles that occur in the floor of the mouth and usually involve the major salivary glands. Specifically, the ranula originates in the body of the sublingual gland, in the ducts of Rivini of the sublingual gland, in the Wharton duct of the submandibular gland, and, infrequently from the minor salivary glands at this location. These lesions are divided into 2 types: oral ranulas and cervical or plunging ranulas. Oral ranulas are secondary to mucus extravasation that pools superior to the mylohyoid muscle, whereas cervical ranulas are associated with mucus extravasation along the fascial planes of the neck.

Pathophysiology

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; the insults include a crush-type injury and 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.

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.1 These factors are further hypothesized to enhance the accumulation of proteolytic enzymes that are responsible for the invasive character of extravasated mucus.2

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.

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.

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 literature3,4,5

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%.6 In a Brazilian study of 1200 children seen at pediatric hospital clinic, the prevalence of mucoceles was 0.08%.7

Mortality/Morbidity

  • 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.8

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.9

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.

Clinical

History

  • Mucoceles are painless, asymptomatic swellings that have a relatively rapid onset and fluctuate in size.
    • They may rapidly enlarge and then appear to involute because of the rupture of the contents into the oral cavity or resorption of the extravasated mucus.
    • The patient may relate a history of recent or remote trauma to the mouth or face, or the patient may have a habit of biting the lip. However, in many cases no insult can be identified.
    • When lesions occur on the anterior ventral surface of the tongue, tongue thrusting may be the aggravating habit, in addition to trauma.
    • The duration of the lesion is usually 3-6 weeks; however, it may vary from a few days to several years in exceptional instances.
  • Patients with superficial mucoceles report small fluid-filled vesicles on the soft palate, the retromolar pad, the posterior buccal mucosa, and, occasionally, the lower labial mucosa.
    • These vesicles spontaneously rupture and leave an ulcerated mucosal surface that heals within a few days.
    • Several lesions may be present, and they range from being nontender to painful.
    • Some individuals note a pattern of development during mealtime.
    • Often, an individual may rupture or unroof the vesicles by creating a suction pressure.
    • Typically, affected individuals report a chronic and recurrent history.
    • Frequently, the patient has a history of lichen planus,10 lichenoid drug reaction, or chronic graft versus host disease involving the oral mucosa.11
  • Individuals with an oral ranula may complain of swelling of the floor of the mouth that is usually painless. The mass may interfere with speech, mastication, respiration, and swallowing because of the upward and medial displacement of the tongue. When oral ranulas are large, the tongue may place pressure on the lesion, which may interfere with submandibular salivary flow. As a result, obstructive salivary gland signs and symptoms may develop, such as pain or discomfort when eating, a feeling of fullness at that site, and increased swelling of the submandibular gland.
  • In individuals with a cervical ranula, an enlarging asymptomatic neck mass is reported.
    • Although trauma to the floor of the mouth or neck region is thought to be associated with the development of a ranula, a specific incidence is usually not identified. In some cases, the individual may have a prior history of a previously removed sialolith, other oral surgical procedures at the floor of the mouth, or transposition of the submandibular ducts for the management of severe drooling. A ranula from improper placement of mandibular implants has been reported.12
    • Congenital anomalies, such as ductal atresia or failure of canalization of the excretory ducts, may contribute to the development of ranulas in infants. In large cervical ranulas, dysphagia and respiratory distress may be the chief complaints.
    • The patient may have a history of a preceding oral swelling (45%) or a concurrent oral mass at presentation (34%). One fifth of patients with cervical ranula have only a cervical swelling, lacking an oral ranula or a history of an oral ranula.
  • The mucus retention cyst appears as a superficial asymptomatic swelling that is usually not associated with a history of trauma.
    • These cysts tend to have variable growth rates, and they do not fluctuate in size.
    • When the mucus retention cyst involves the submandibular gland, Wharton duct, or Stensen duct, obstructive disease may occur and a pattern of gustatory swelling and pain may be reported.

Physical

The clinical features associated with mucoceles include a nontender, mobile, dome-shaped enlargement with intact epithelium that lies over it. Superficial lesions take on a bluish to translucent hue, whereas deep lesions have normal mucosal coloration. Bleeding into the swelling may impart a bright red and vascular appearance. The mucosa lining is usually intact; however, repeated sucking on the lesion may result in a white, rough, keratotic surface. Occasionally, a punctate sinus tract is observed from which mucoid material is expressed. Palpation reveals a fluctuant mass that does not blanch on compression. An inflammatory response is usually not detected at clinical examination unless it has been irritated recently. Most are less than 1.5 cm in diameter. Although the mucocele can occur anywhere in the oral cavity where minor salivary glands are present, approximately 75-80% of the cases occur on the lower lip, followed by the floor of the mouth, ventral tongue, and buccal mucosa.


Classic example of a mucocele in a child. The flu...

Classic example of a mucocele in a child. The fluctuant, translucent-blue nodule on the lower labial mucosa has been present for 6 weeks. Trauma from sucking on the lower lip was suspected to be the cause.

Classic example of a mucocele in  a child. The flu...

Classic example of a mucocele in a child. The fluctuant, translucent-blue nodule on the lower labial mucosa has been present for 6 weeks. Trauma from sucking on the lower lip was suspected to be the cause.

  • The Blandin and Nuhn mucocele occurs exclusively on the anterior ventral surface of the tongue at the midline. Although the lesions may have clinical features similar to those of the mucocele, which is found elsewhere, they tend to be more polypoid with a pedunculated base. Because of repeated trauma against the lower teeth, the surface may be red and granular or white and keratotic.


Mucocele on the midline ventral surface of the to...

Mucocele on the midline ventral surface of the tongue involving the glands of Blandin and Nuhn.

Mucocele on the midline ventral  surface of the to...

Mucocele on the midline ventral surface of the tongue involving the glands of Blandin and Nuhn.

  • Superficial mucoceles appear as single or multiple tense vesicles with intact delicate mucosa. They are transparent, mucous filled, and dome shaped. The lesions tend to persist for several days, rupture spontaneously, and heal a few days after they rupture. Usually, only mild discomfort occurs, but some cases are painful. Concurrent lichenoid disorders have been reported.13 Superficial mucoceles are typically 1-4 mm in diameter.


Example of 2 superficial mucoceles of the soft pa...

Example of 2 superficial mucoceles of the soft palate in a 50-year-old woman. The red lesion represents a recently ruptured mucocele, and the translucent papular lesion represents an intact mucocele.

Example of 2 superficial  mucoceles of the soft pa...

Example of 2 superficial mucoceles of the soft palate in a 50-year-old woman. The red lesion represents a recently ruptured mucocele, and the translucent papular lesion represents an intact mucocele.

  • The oral ranula is a relatively large unilateral blue to translucent mass in the floor of the mouth that remotely resembles the belly of a frog (Rana species). The lesion may cross the midline when especially large, making the offending salivary gland difficult to localize. Large oral ranulas superiorly and medially displace the tongue. The consistency of the lesion is that of mucus, and the lesion does not blanch on compression. If the mass is located in the deeper aspect of the floor of the mouth, it loses its bluish translucent color. Most commonly, ranulas arise from the sublingual gland and, infrequently, from the submandibular gland.


Unilateral oral ranula in a young adult manifesti...

Unilateral oral ranula in a young adult manifesting as a purple swelling.

Unilateral oral ranula in a  young adult manifesti...

Unilateral oral ranula in a young adult manifesting as a purple swelling.

  • The cervical ranula appears as an asymptomatic, continuously enlarging mass that may fluctuate in size. The overlying skin is usually intact. The mass is fluctuant, freely movable, and nontender. The mass is not associated with the thyroid gland or lymph node chains. In some instances, detecting salivary gland herniation of a portion of the sublingual gland through the mylohyoid muscle into the neck may be possible. The mass may not be well defined but follows the fascial planes of the neck and may extend into the mediastinum. Similar to the oral ranula, the mass tends to cause a lateral swelling; however, it may cross the midline.
  • The mucus retention cyst has a presentation similar to that of a mucocele and a ranula, except that it does not fluctuate in size. The fluid-filled lesions tend to slowly enlarge with well-defined margins that are freely movable. The dome-shaped nodule has a smooth intact surface that imparts a pink, yellow, blue, or red color. The oral floor is the primary site, especially in the area of the orifices of the Wharton's duct and the caruncles, followed by the buccal mucosa. The lesions are usually 5-15 mm in diameter, but they may be much larger when they involve the sublingual or submandibular gland.

Causes

  • 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 (less often) 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.
    • 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, especially in children.14
  • 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.


Example of a cervical ranula with no oral involve...

Example of a cervical ranula with no oral involvement in an adult. The swelling developed after a car accident in which the individual had trauma to the face and neck.

Example of a cervical ranula  with no oral involve...

Example of a cervical ranula with no oral involvement in an adult. The swelling developed after a car accident in which the individual had trauma to the face and neck.

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

More on Mucocele and Ranula

Overview: Mucocele and Ranula
Differential Diagnoses & Workup: Mucocele and Ranula
Treatment & Medication: Mucocele and Ranula
Follow-up: Mucocele and Ranula
Multimedia: Mucocele and Ranula
References

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