9.1
Ranula
Introduction
A cyst can be defined as a pathologic cavity having fluid, semifluid, or gaseous contents, and not created by accumulation of pus. It does not necessarily have an epithelial or endothelial lining; inclusion of lining in the definition results in a somewhat artificial distinction between pseudocysts and “true” cysts.
Benign cystic lesions of salivary glands may be developmental, degenerative, or neoplastic. In Sections 9.1 and 9.2 , we focus on degenerative lesions that include mucoceles, mucous retention cysts, salivary duct cysts, and the specific entity of ranula.
Ranula presents as a translucent submucosal swelling in the floor of mouth, arising from collection of saliva extravasated from a sublingual salivary gland (SLG). Wiseman stated in 1676 that ranulas could cause a croaking speech, and this, together with the resemblance of the oral ranula to the belly or air sac of a frog, justified the term ranula, meaning little frog (Latin: rana = “frog”; ulus = “small”). If extravasated saliva tracks inferior to the floor of mouth formed by the pair of mylohyoid muscles, the term diving, plunging, or cervical ranula is applied.
Relevant Anatomy
The anatomy of the sublingual space dictates the pathogenesis of ranula and the rationale behind its definitive treatment. The SLG consists of unencapsulated mucinogenic glandular tissue lying within areolar tissue between the mylohyoid muscle and oral mucosa. Several lesser sublingual glands commonly drain through individual ducts of Rivinus into plica sublingualis. Greater SLG, if present, lies posteromedial to the lesser glands and drains via Bartholin’s duct into either Wharton’s duct or directly into the caruncula sublingualis.
Over 40% of cadavers have a dehiscence in the mylohyoid muscle that can allow herniation of the SLG or saliva extravasation into the neck.
Pathogenesis
Harrison has proposed two theories for pathologenesis: extravasation of mucus through damaged duct of Rivinus or from herniated SLG, secondary to trauma or obstruction. The SLG secretes mucinous saliva spontaneously without the need of neurological stimulus. Outside the confines of the sublingual gland and duct system, extravasated saliva is only limited by either the space between mylohyoid and mucosa in the oral cavity or by inflammatory fibrosis within tissues in the neck and removal of mucin by macrophages. The former process forms a simple ranula and the latter forms a plunging ranula, both bounded by inflammatory granulation tissue, not epithelium. Epidemiologic study has revealed a high risk of plunging ranula among Maori and Pacific Islanders.
Clinical Presentation
Most ranulas appear within the first three decades of life. Common presenting features are disruption to normal oral function from floor of mouth swelling ( Fig. 9.1.1 ), and cosmetic concerns in cases of plunging ranula ( Fig. 9.1.2 ). Specific history of trauma is usually absent. Episodes of increase in swelling associated with pain and tenderness secondary to inflammation may occur. Indeed, many misdiagnosed cases of plunging ranula may undergo incision and drainage for a presumed (dental) abscess that turns out to be an inflamed pseudocyst.
Differential Diagnosis
Differential diagnosis for this clinical presentation includes abscess, simple (e.g., dermoid) cyst, thyroglossal duct cyst, cystic hygroma, lymphangioma, and lipoma. Clinical diagnosis of ranula is usually straightforward. However, diagnostic errors may still arise. Atypical presentation may confound, as described by Abt et al., who reported a case of plunging ranula with direct extension to the prestyloid parapharyngeal space, masticator space, and parotid gland without involving the submandibular space.
Investigations
It is recommended that aspiration of cervical ranula be performed. Testing of classical thick, mucinous aspirate for presence of salivary amylase, after dilution with normal saline, confirms the diagnosis. Radiological confirmation can be performed with ultrasonography ( Fig. 9.1.3 ). MRI scan is recommended for recurrent or atypical cases.
Management of Ranula
The focus for treatment is generally removing the sublingual gland or sclerotherapy with OK-432. For simple ranula, there are various treatments. We favor micromarsupialization, a minimally invasive procedure, in which a suture is passed through the lesion at its greatest diameter. This forms an epithelialized tract through which the accumulated saliva drains. If this fails, definitive treatment by SLG excision is recommended.
Definitive Surgical Technique
SLG excision is performed transorally via an incision in the floor of mouth, in line with the submandibular duct on its lingual aspect. Mucosa overlying the SLG is then dissected off the gland using sharp dissection. Traction is then applied to the gland and blunt dissection will identify Wharton’s duct and lingual nerve. These structures are gently reflected off the gland and any sublingual (Bartholin’s) duct encountered is divided. The gland is then dissected from its bed.
A fibrous tract is usually encountered passing through a dehiscence of the mylohyoid muscle ( Fig. 9.1.4 ). Some patients have obvious herniation of the SLG through this dehiscence. Occasionally, the pseudocyst tracks around the posterior free margin of the mylohyoid, rather than passing directly through the dehiscence. The tract is followed into the neck and any residual collection may be expressed through the dehiscence into the mouth ( Fig. 9.1.5 ).
Outcomes
In our series of 81 plunging ranulas, we had a 99% success rate by excising the sublingual gland alone. That has since been augmented by a further 53 published cases with no recurrence. If the SLG is not completely excised, a recurrence of ranula is possible.
Most complications are minor and consist of postoperative infection or bruising in submandibular space that settles quickly. Two patients in our series suffered inadvertent trauma to Wharton’s duct leading to excision of the submandibular gland. Seven patients experienced lingual nerve neuropraxia.
- •
Two theories for pathologenesis: extravasation of mucus through damaged duct of Rivinus or from herniated SLG, secondary to trauma or obstruction.
- •
If the SLG is not completely excised, a recurrence of ranula is possible.
9.2
Other Benign Cystic Salivary Lesions
Mucocele
Mucoceles, also called extravasation mucoceles or mucous escape reaction, are the most common lesions that occur on the lower lip in males in the second to third decade of life. Submucosal spillage of mucin imparts a bluish translucent color to the swelling. These lesions present with a history of intermittent rupture.
Habits such as lip biting may favor mucocele development in the lower lip. Also, compared with the upper lip, the lower lip has greater mass and moves more during speech. Finally, the greater number and density of salivary glands in the lower lip may play a role in the predilection for mucoceles in the lower lip.
The term “extravasation mucocele” has an initial stage (interstitial mucus lakes), a resorption stage (mucus granulomas with macrophages, foam cells, and foreign bodies giant cells), and a terminal stage with the development of a pseudocyst (capsule of collagen tissue, no epithelial demarcation).
A variant called superficial mucocele is seen in other parts of the oral cavity such as soft palate or retromolar trigone and may be associated with lichenoid inflammation such as lichen planus, lichenoid drug eruptions, and chronic graft-versus-host disease.
Some mucoceles are short-lived lesions that rupture and heal by themselves. Many lesions, however, are chronic and surgical excision is necessary. To minimize the risk of recurrence, any adjacent minor salivary glands that may be feeding into the lesion should also be removed. Excised tissue should be submitted for microscopic examination to confirm the diagnosis. The prognosis is excellent, although mucoceles will occasionally recur, especially if feeding glands are not removed.
Mucous Retention Cyst
Mucous retention cysts or retention mucoceles are developmental lesions with a complete epithelial lining and are filled with mucus with no inflammatory reaction. They can occur anywhere in the oral cavity, typically in an older female patient.
Salivary Duct Cyst
These resemble mucous retention cysts, having an epithelial lining, but are not developmental in origin. Rather, partial obstruction of salivary flow is postulated to be the trigger. This either leads to increased luminal pressure and proximal dilatation or incites oncocytic metaplasia as a response to the obstruction.
Isolated salivary duct cysts are treated by conservative surgical excision. For cysts in the major glands, partial or removal of the gland may be necessary.
For rare patients who develop multifocal salivary ductal ectasia, excision may be performed for the more problematic swellings. However, surgical management does not appear feasible for all lesions, which may number as many as 100. In some cases, systemic antibiotics and disinfectant mouth rinses can be helpful in relieving pain and reducing drainage of pus. Sialagogues may stimulate salivary flow, thereby preventing the accumulation of inspissated mucus within the dilated excretory ducts.
Kussmaul Disease or Sialodochitis Fibrinosa
This rare disease is characterized by recurrent swelling of the salivary glands, which then discharge clots of fibrin into the oral cavity. First described by Kussmaul in 1879, it also typically includes history of allergy, elevated blood eosinophils or serum immunoglobulin E (IgE), mucofibrous ductal plugs, and stromal infiltration of lymphocytes or eosinophils. Autoimmune diseases and other causes of ductal obstruction do need to be ruled out.
Management depends on severity of clinical picture. Rehydration and massage form the mainstay of treatment for milder cases. Dilatation of the duct and irrigation with saline or steroid-saline solution may be used as second-line treatment. Antihistamine and steroid therapy to address allergies is often useful.
