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Ranula

Ranula is rare benign acquired cystic lesion that occurs at the floor of mouth. It results from obstruction of a sublingual gland or adjacent minor salivary gland with resultant formation of a mucous retention cyst 1,5. A ranula can be classified based on its extent:

  1. simple ranula: these ranulas are confined to the sublingual space
  2. plunging ranula
    • also known as diving ranula or cervical ranula
    • as a simple ranula enlarges it dissects along facial planes beyond the confines of the sublingual space, either:
      • around the posterior edge of the mylohyoid muscle, or
      • directly thought a deficiency of the mylohyoid muscle

Epidemiology

Ranulas arise either spontaneously or as a result of trauma to the floor of mouth, including surgery. For reasons that are unclear, they appear to be more common in the Maori of New Zealand and Pacific Island Polynesians 7.

Clinical presentation

Ranulas present as a mass either in the floor of mouth, where they elevate the mucosa often with a 'bluish' tinge, or in the neck 7.

Pathology

Whether a ranula is 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 2,5,7. Where there is no history of previous infection or haemorrhage, they tend to be thin walled, unilocular, homogeneous cystic lesions 1.

The fluid within a ranula closely resembles that of the normal secretions of the sublingual glands 5.

Radiographic features

The key to diagnosing a ranula, especially in cases where they are large and have dissected some distance away form their origin, is 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 1.

Ultrasound

Uncomplicated ranulas appear as thin walled cystic lesion, 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 lesion with central fluid attenuation (10-20HU). If the cysts have been intervened upon previously or have been infected then the content may be increased in attenuation, even occasionally resembling a non-enhancing soft tissue mass. The walls of such lesions are typically thicker 7.

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

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

If a sialogram of the submandibular duct (which receives tributaries from some of the sublingual ducts) is performed, no communication with the cyst is usually identified 7.

Treatment and prognosis

Surgical resection is curative but requires not only excision of the cystic component but also of the parent sublingual gland. If the gland is left in situ then recurrences may occur 5. This was highlighted by Parekh et al 3 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 6.

Differential diagnosis

The differential depends on the location of ranula, but in general includes the following entities:

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