Ranulas are a rare benign acquired cystic lesion that occur at the floor of mouth.
For reasons that are unclear, they appear to be more common in the Maori of New Zealand and Pacific Island Polynesians 7.
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.
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 1,5. 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
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.
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. 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".
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.
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.
- 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 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.
The differential depends on the location of ranula, but in general includes the following entities:
- 1. Coit WE, Harnsberger HR, Osborn AG et-al. Ranulas and their mimics: CT evaluation. Radiology. 1987;163 (1): 211-6. Radiology (abstract) - Pubmed citation
- 2. Kurabayashi T, Ida M, Yasumoto M et-al. MRI of ranulas. Neuroradiology. 2000;42 (12): 917-22. Neuroradiology (link) - Pubmed citation
- 3. Parekh D, Stewart M, Joseph C et-al. Plunging ranula: a report of three cases and review of the literature. Br J Surg. 1987;74 (4): 307-9. Pubmed citation
- 4. Dähnert W. Radiology Review Manual. Lippincott Williams & Wilkins. (2007) ISBN:0781766206. Read it at Google Books - Find it at Amazon
- 5. Charnoff SK, Carter BL. Plunging ranula: CT diagnosis. Radiology. 1986;158 (2): 467-8. Radiology (abstract) - Pubmed citation
- 6. Rho MH, Kim DW, Kwon JS et-al. OK-432 sclerotherapy of plunging ranula in 21 patients: it can be a substitute for surgery. AJNR Am J Neuroradiol. 2006;27 (5): 1090-5. AJNR Am J Neuroradiol (full text) - Pubmed citation
- 7. Som PM, Curtin HD. Head and neck imaging. Mosby Inc. (2003) ISBN:0323009425. Read it at Google Books - Find it at Amazon