Ranulas and Plunging Ranulas

Frequency

Ranulas occur infrequently and tend to present early in life, most often in the first, second, or third decade.

Sex

The reported male-to-female ratio is 1:1.3, without significant side preference.

Ranulas

Congenital ranulas may arise secondary to an imperforate salivary duct or ostial adhesion. These are quite rare and have been known to spontaneously resolve.[3]

Posttraumatic ranulas arise from (presumed) trauma to the sublingual gland, leading to mucus extravasation and formation of a pseudocyst. The more appropriate term for this may be mucus extravasation reaction (MER).

Plunging ranulas

Plunging ranulas generally appear in conjunction with oral ranulas, although in rare cases they arise independently, without the oral component. Other terms for plunging ranula include deep, diving, cervical, and deep plunging ranula, as well as oral ranula with cervical extension. These lesions are characterized by mucus extravasation, with extension below the mylohyoid muscle and visible extraoral neck swelling. A congenital dehiscence in the mylohyoid muscle has been suggested as an etiology.[4]

Ranulas

Ranulas can form as a result of partial obstruction of a sublingual duct, leading to formation of an epithelial-lined retention cyst. This is unusual, occurring in less than 10% of all ranulas.

Ranulas can also result from trauma leading to the formation of extravasated saliva. Experimentally, partial severance or ligation of the sublingual duct leads to ranula formation, whereas ligation of the submandibular duct does not. The ligation of the parotid duct ultimately leads to atrophy. The difference lies in the fact that the sublingual gland secretes continuously in the interdigestive period and appears to be able to secrete against a gradient, whereas the other two major salivary glands secrete only in response to stimuli such as eating. Therefore, with trauma, if the sublingual duct is obstructed, secretory back pressure builds and acini rupture, leading to mucus extravasation. Alternately, trauma causing direct damage to the duct or acini can lead to mucus extravasation, with subsequent pseudocyst formation.

Plunging ranulas

Plunging ranulas arise in the neck by one of 3 mechanisms:

• The sublingual gland may project through the mylohyoid, or an ectopic sublingual gland may exist on the cervical side of the mylohyoid. This explains most plunging ranulas that exist without an oral component.

• The pseudocyst may penetrate through the mylohyoid. Up to 27-45% of mylohyoid muscles in cadavers are found to be dehiscent, usually in the anterior two thirds of the muscle. These sites of dehiscence provide a route of egress for the cyst. In some instances, surgical trauma from initial ranula operations may scar or fibrose the superior surface of a ranula. When the ranula recurs, the path of least resistance is through a dehiscent mylohyoid, and a plunging ranula forms when only a simple ranula was present initially. Up to 44% of all plunging ranulas are iatrogenically induced in this manner.

• A duct from the sublingual gland may join the submandibular gland or its duct, allowing ranulas to form in continuity with the submandibular gland. Therefore, the ranula accesses the neck from behind the mylohyoid muscle.

Ranulas

A ranula is most commonly observed as a bluish cyst located below the tongue as seen in the images below. It may fill the mouth and raise the tongue. Typically, these are painless masses that do not change in size in response to chewing, eating, or swallowing. Occasionally, pain may be involved. (See the images below.)

Plunging ranulas

Plunging ranulas can manifest as neck swelling in conjunction with, or independent of, a floor-of-mouth cyst. Occasionally, squeezing the mass causes swelling in the floor-of-mouth cyst. Most reported plunging ranulas are 4-10 cm in size and are usually found in the submandibular space. They have been reported to extend into the submental region, the contralateral neck, the nasopharynx up to the skull base, the retropharynx, and even into the upper mediastinum.[5, 6]

See Surgical therapy.

The sublingual gland lies against the sublingual depression of the mandible and directly on the mylohyoid. The submandibular duct (Wharton duct) and the lingual nerve lie posterior and medial to the gland. The genioglossus muscle is medial to these structures. No posterior fascial limits to the sublingual space exist, which allows lesions to exit the sublingual space and enter into the submandibular or parapharyngeal space.

The sublingual gland is unique among the major salivary glands in that it lacks a true capsule and is more consistent with a significant conglomeration of many smaller glands. The sublingual gland is drained by a collective of minor ducts known as the ducts of Rivinus (especially anteriorly), which open into the floor of the mouth, usually along the sublingual fold. At times, several ducts may coalesce and form a more substantive duct termed the Bartholin duct, which often joins the submandibular duct proximal to the sublingual caruncle.

Although some have advocated surgical management of congenital ranulas, recent literature supports observation in asymptomatic patients. Many congenital ranulas resolve on their own and do not require surgical intervention.

Recurrence of the ranula is possible despite surgical excision. Some ranulas have been noted to resolve spontaneously.

CT scanning

Ranulas on CT scanning (as seen in the image below) are described as cystic masses in the submandibular or parapharyngeal space that extend into or abut the sublingual space. On CT scanning, they are noted to be sharply demarcated lesions of low attenuation that conform to their local fascial boundaries. They are generally unilocular in nature. With the exception of a sublingual epidermoid, the appearance of a simple ranula on CT scanning is distinctive.[1]

Plunging ranulas are occasionally noted on CT scanning to have a small tail extending into the sublingual space. This finding is almost pathognomonic for plunging ranulas. If this is absent, the presence of a homogeneous cyst in the submandibular or parapharyngeal space that abuts the sublingual space is highly indicative of a plunging ranula.

MRI

MRI is the most sensitive imaging study for evaluation of the sublingual gland and its pathologic states. On T1-weighted MRI scans, the gland appears as an area of intermediate signal intensity, lower than adjacent fat but higher than muscle. T2-weighted images help discriminate cysts from surrounding normal structures.[7]

Ultrasonography

High-resolution ultrasonography is a noninvasive test with no known biologic cost that has been demonstrated to be quite successful in evaluating cystic lesions of the submandibular region in young people, with particular utility in the plunging ranula. In addition to confirming the cystic nature of the lesion, the mylohyoid muscle integrity also can be elucidated.[2]

A study by Jain found that out of 126 patients with surgically proven plunging ranulas, only two showed tail sign on imaging, with both demonstrating fluid in the posterior sublingual space on ultrasonography and only one patient showing all of the classic components of tail sign. In this individual, fluid exclusively in the posterior sublingual space extended into the submandibular space over the mylohyoid muscle’s posterior free edge.[8]

Needle aspiration findings are as follows:

• Analysis of fluid from ranulas demonstrates mucus with prominent histiocytes.

• The biochemistry of this fluid shows high amylase and protein content.

Most ranulas demonstrate a cyst devoid of epithelial lining, with the wall composed of vascular fibroconnective tissue resembling granulation tissue. Histiocytes predominate the pseudocyst wall. Mucin and foamy macrophages are often observed. Occasionally, partial epithelial linings are observed.

Sclerotherapy, most often with OK-432 or bleomycin, has become more commonly reported in the scientific literature.[9, 10]  OK-432 contains a particular strain of group A Streptococcus pyogenes that presumably works through local inflammatory responses and may require multiple injections. Effectiveness, with reduction or elimination of the lesion, has been demonstrated in over 90% of patients in some sclerotherapy trials, and both intraoral and plunging ranulas have been successfully treated.[9, 11]  Studies have reported that nearly half of all patients experienced local pain and fever, which resolved over a few days. OK-432 sclerotherapy may be considered as a first-line treatment option in experienced centers.

Congenital ranulas

Some have advocated that all patients with submandibular duct obstruction leading to ranula formation need early marsupialization and ductoplasty to prevent complications such as sialoadenitis.

Evidence exists that imperforate ducts may spontaneously resolve if rupture takes place during feeding. Therefore, observation for spontaneous resolution of congenital ranulas is reasonable. If airway obstruction or feeding problems arise, surgery is indicated.[12]

Ranulas

Marsupialization

Simple marsupialization is the oldest and most widely reported treatment for ranulas. It involves unroofing the cyst and tacking the edges of the cyst to adjacent tissue. Failure rates range from 61-89%, with cysts recurring anywhere from 6 weeks to 12 months later. Inferior compression on the cyst from the tongue leads to premature closure of the opened cyst. This increases the risk of the cyst recurring. Packing the cyst cavity with gauze for 7-10 days improves the success rate.[13] In one report, 11 of 12 patients had resolution of their ranula with marsupialization and subsequent packing of the cavity.

In a prospective study, Woo et al reported that micromarsupialization is an effective initial treatment for oral ranulas, with resolution of the ranulas occurring in all 20 of the trial’s patients. The ranulas recurred in five patients, with two patients again showing recurrence 6 months after revision, prompting resection of the ranula and sublingual gland.[14]

Placement of suture or Seton[15]

With micro-marsupialization, a silk suture or Seton can be placed through the surface of the ranula under local anesthesia. This is left in place a minimum of 7 days while an epithelial tract forms to allow for mucus drainage between the surface and the underlying salivary glandular tissue. Morbidity is minimal to nonexistent, and recurrence or treatment failure is the primary complication. This can also be performed in the office.

Carbon dioxide laser[16]

The carbon dioxide laser has been used with limited patients with good success to remove the cyst and scar the gland enough to decrease risk for recurrence. A tissue biopsy is recommended first to confirm the diagnosis of ranula.

Radiation therapy[17]

In the rare patient who cannot tolerate surgery, radiation therapy is a viable alternative. Low doses, from 20-25 grays (Gy), are effective. Xerostomia can be avoided with low-dose therapy and shielding of the contralateral parotid gland. The risk of radiation-induced malignancy is real but small.

Sublingual gland excision

The criterion standard for treatment of ranulas is excision of the sublingual gland. This removes the source of the mucus and thus significantly decreases the risk for recurrence.[18] A review of 580 patients with ranulas and plunging ranulas found that recurrence rates varied greatly depending on the surgical method chosen. Marsupialization, excision of the ranula alone, and excision of the sublingual gland combined with the ranula resulted in recurrence rates of 66.67%, 57.69%, and 1.20% respectively.[19]

Plunging ranulas

Transoral approach

This provides better access for complete removal of the sublingual gland. If ectopic sublingual gland is present on the cervical surface of the mylohyoid, this may be missed without exploring the undersurface of the muscle. Some surgeons advocate simply draining the cervical portion of the ranula and excising the gland transorally. Complete excision of the cyst is not necessary if the gland itself is excised. A biopsy of the cyst wall is recommended for tissue confirmation.

Yang and Hong reported in a prospective study that an intraoral surgical approach can safely and effectively be used to remove plunging ranulas. During the median 14-month follow-up period, none of the study’s 23 patients experienced a recurrence.[20]

Transcervical approach

Complete removal of the sublingual gland is difficult with this approach, requiring division of the mylohyoid muscle and dissection up to the floor of the mouth. Some surgeons recommend a transoral excision of the gland with drainage of the cyst first. If that is unsuccessful, complete excision of the cyst via a transcervical approach is indicated. A transcervical approach is also indicated for ranulas located exclusively in the neck.

Some authors advocate the injection of methylene blue into the ranula at the start of the procedure to improve the preservation of vital surrounding structures. Care must be taken in injecting the dye to avoid extravasation into surrounding tissue.[21]

Dilation and cannulation of the sublingual caruncle and submandibular duct (Wharton duct) with lacrimal probes is useful, when achievable, to accentuate the ductal course and prevent injury. The plane of dissection medially is of particular interest because of the lingual nerve and submandibular duct. Of note, the lingual nerve crosses the submandibular duct twice, coursing lateral to and under the duct before rising into the tongue medial to it.

Note the preoperative, intraoperative, and postoperative images below.

Ranulas

Risks include paraesthesia of the lingual nerve (up to 25% in some studies), injury to the Wharton duct with the possibility of obstructive sialadenitis, and ductal laceration leading to salivary leakage. In a study of 571 patients who underwent 606 procedures for ranulas, the most common complications included recurrence of the ranula (5.78%), lingual nerve injury resulting in sensory deficit of the tongue (4.89%), and damage to Wharton's duct (1.82%).[22] Other complications included hematoma, infection, and dehiscence of the wound, all of which were uncommon. The tongue numbness generally resolves over the course of six months.

Plunging ranulas

Risk for paresis and paralysis of the marginal mandibular nerve is increased because the nerve often lies just on the surface of the cyst. Drainage of the cyst following identification of the nerve can often reduce risk for postoperative complications.

A literature review by Chung et al assessing different treatment approaches to ranulas formed from salivary extravasation found intraoral resection of the sublingual gland to be an effective means of oral ranula cure. Although cure rates obtained through micromarsupialization and its modification were comparable to those associated with sublingual gland resection, the results showed moderate inconsistency. With regard to plunging ranulas, the cure rates for the intraoral and transcervical surgical approaches did not significantly differ, but the rates for both techniques were superior to that for OK-432 sclerotherapy. The investigators found fewer complications associated with the intraoral approach to sublingual gland resection than with transcervical surgery.[23]

The overall risk for recurrence when the sublingual gland is not excised has been reported to be in excess of 50%. This rate drops to as low as 2% if the gland is excised. Because the risk to adjacent structures is higher for gland-excising procedures, a trial of less-invasive procedures is advocated by some. Smaller cysts (< 1.5 cm) are usually more superficial in nature and may respond more readily to marsupialization. Larger cysts are more closely associated with the gland and usually require gland excision in association with cyst removal.

Obtaining a specimen for pathology is essential, not only for histologic confirmation but also because the presence of squamous cell carcinoma arising in the cyst wall of a ranula[24] and papillary cystadenocarcinoma of the sublingual gland presenting as a ranula have been reported.[25]