Mundbodenzyste (Ranula)

Imaging of

the sublingual and submandibular spaces. Simple ranula. a Axial and b coronal contrast-enhanced CT images demonstrate a well-circumscribed fluid attenuation lesion within the left sublingual space (*)

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Imaging of

the sublingual and submandibular spaces. Sublingual space ranula. a Axial T2-weighted MR image shows a high-signal lesion within the left sublingual space. b Axial diffusion-weighted image and c ADC map demonstrates lack of restricted diffusion, confirming the diagnosis (as opposed to an epidermoid, which would have restricted diffusion)

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Imaging of

the sublingual and submandibular spaces. Plunging ranula. Axial contrast-enhanced CT images of the floor of the mouth illustrates a well-circumscribed cystic lesion predominantly occupying the left submandibular space causing a mass effect on the left submandibular gland (a, arrow). A more superior image reveals a small portion of the lesion based in the sublingual space, referred to as the “tail sign” (b, arrowheads)

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Radiopaedia • CC-by-nc-sa 3.0 • de

Ranulas are rare, benign, acquired, cystic lesions that occur at the floor of the mouth as sublingual or minor salivary gland retention cysts.

Epidemiology

For reasons that are unclear, they appear to be more common in the Maori of New Zealand and Pacific Island Polynesians .

Clinical presentation

Ranulas present as a mass either in the floor of the mouth, where they elevate the mucosa, often with a bluish tinge, or in the neck .

Pathology

Ranulas arise either spontaneously or as a result of trauma to the floor of mouth, including surgery. They result from obstruction of a sublingual gland or adjacent minor salivary gland with resultant formation of a mucous retention cyst. A ranula can be classified based on its extent:

simple ranula: confined to the sublingual space
plunging ranula (also known as diving ranula or cervical ranula): extends into the submandibular space
- as a simple ranula enlarges it dissects along fascial planes beyond the confines of the sublingual space, either:
  - around the posterior edge of the mylohyoid muscle, or
  - directly through a deficiency of the mylohyoid muscle (mylohyoid boutonniere)

Whether simple or of the diving/plunging type, most ranulas have no epithelial lining and are simply pseudocysts lined by a condensation of connective tissue at the periphery of the collection, formed in response to the inflammatory effect of the salivary secretions . Where there is no history of previous infection or hemorrhage, they tend to be thin-walled, unilocular, homogeneous cystic lesions .

The fluid within a ranula closely resembles that of the normal secretions of the sublingual glands .

Radiographic features

The key to diagnosing a ranula, especially in cases where they are large and have dissected some distance away from their origin, is the identification of a connection to the sublingual space. This may be no more than a thin tail of fluid or a significant local fluid collection . Simple ranula is within the sublingual space above the mylohyoid muscle but plunging ranula dives into the submandibular space with a collapsed sublingual portion called the "tail".

Fluoroscopy

If a sialogram of the submandibular duct, which receives tributaries from some of the sublingual ducts, is performed, usually no communication with the cyst is identified .

Ultrasound

Uncomplicated ranulas appear as thin-walled cystic lesions, and can be imaged both from the skin or trans-orally with a small probe. If infected, the walls are thicker and the fluid content more echogenic.

CT

Uncomplicated ranulas appear as thin-walled cystic lesions with central fluid attenuation (10-20HU). If the cysts have been intervened upon previously or have been infected, the content may be increased in attenuation, even occasionally resembling a non-enhancing soft tissue mass. The walls of such lesions are typically thicker .

If a superimposed infection is present at the time of imaging, they will be indistinguishable from an abscess, with thicker walls and surrounding fat stranding.

MRI

T1: low signal
T2: high signal
T1 C+ (Gd): the wall may demonstrate some enhancement (best seen with fat saturation)

Treatment and prognosis

Surgical resection is curative but requires not only excision of the cystic component but of the parent sublingual gland as well. If the gland is left in situ, the ranula may recur . This was highlighted by Parekh et al. ,who observed the following recurrence rates:

incision and drainage: 70% recurrence
marsupialization: 53% recurrence
excision of the lesion in the neck: 85% recurrence
excision of the lesion in the neck and sublingual gland: 3.8% recurrence
intraoral excision of the sublingual gland and drainage of the cyst: 0% recurrence

Sclerotherapy with OK-432 (picibanil: a lyophilized mixture of a low virulence strain (Su) of Streptococcus pyogenes incubated with benzylpenicillin) has also been used with good effect .