Ranula Radiology: Simple vs Plunging Ranula on Ultrasound, CT and MRI

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A ranula is a collection of saliva in the floor of the mouth that comes from the sublingual gland. Most are not true cysts at all: the gland or its ducts are disrupted, mucus leaks into the surrounding tissue and walls itself off, so the lesion is a mucus extravasation pseudocyst with no epithelial lining. When the collection stays above the mylohyoid muscle it is a simple (oral, sublingual) ranula. When it reaches the submandibular space it is a plunging (diving, cervical) ranula.

On imaging the lesion itself is easy: a thin-walled, unilocular, fluid-density or fluid-signal collection that does not enhance unless it is infected. The two things that actually change what happens to the patient are harder, and they are what your report should settle. First, does the collection cross the mylohyoid sling, because that is what separates a simple from a plunging ranula. Second, is the sublingual gland involved, because removing that gland is the step that stops the lesion coming back, and recurrence after treatment that leaves the gland in place runs at 15 to 30 percent.

At a glance
What it is	Extravasated saliva from the sublingual gland, walled off as a pseudocyst; a true epithelium-lined retention cyst is the minority
Origin	Sublingual gland almost always; minor salivary glands of the floor of the mouth occasionally
Simple (oral) ranula	Confined to the sublingual space, above the mylohyoid muscle
Plunging (diving) ranula	Extends into the submandibular space, usually through a defect in the mylohyoid muscle
Relative frequency	About 4 in 5 are oral and 1 in 5 plunging in a 207-lesion ultrasound series
Typical patient	Second and third decades; children are common; equal sex distribution
Trigger	Blunt trauma to the floor of the mouth or neck, dental or oral surgery, or no identifiable cause
First-line imaging	Ultrasound. CT or MRI to map extent, to reach the deep margin, or when an epidermoid is in the differential
Signature CT or MRI finding	Tail sign: a thin collapsed band of the collection tracking back into the sublingual space. Useful when present, absent in most cases
Content on aspiration	Viscous, straw-coloured, amylase-rich mucus. Aspiration alone is not treatment
Definitive treatment	Transoral excision of the sublingual gland, complete rather than partial
Malignant potential	None

Ranula at a glance: the points a head and neck report has to cover.

Sagittal, coronal and axial CT of a simple ranula filling the sublingual space as a well-defined low-attenuation cyst — Simple (sublingual) ranula on CT in the sagittal, coronal and axial planes: a large, well-defined, unilocular fluid-attenuation collection filling the sublingual space above the mylohyoid muscle and crossing the midline, with no solid component and no septations.

Quiz

Which of the following is TRUE with regards to a ranula?

Can undergo malignant transformation
Most commonly congenital in etiology
Arises from the sublingual or minor salivary glands
Cyst aspiration is the treatment of choice

Click here for the answer

Answer: 3. A ranula arises from the sublingual gland, or less often from a minor salivary gland of the floor of the mouth. It has no malignant potential, it is acquired rather than congenital in almost every case, and aspiration alone has the highest recurrence rate of any treatment because it removes the saliva without removing the gland that is leaking it.

What is a ranula?

Two mechanisms are described, and the distinction matters because it explains why some treatments fail. In the retention cyst, a sublingual duct is obstructed and the duct dilates behind the obstruction, so the wall is lined by epithelium and the lesion is a true cyst. In the extravasation pseudocyst, the gland or duct is torn, saliva escapes into the connective tissue and a wall of granulation tissue and compressed fibrous tissue forms around it, so there is no epithelial lining at all. Quick and Lowell separated these two varieties in 1977 and the extravasation pseudocyst is the common one in practice, for both oral and plunging lesions.

The consequence is practical. You cannot cure a pseudocyst by removing its wall, because the wall is not the problem: the leaking gland is. That is why marsupialisation and aspiration recur, why excising the cyst without the gland recurs, and why every current series converges on taking out the sublingual gland itself.

The old teaching that a simple ranula is a true cyst while only a plunging ranula is a pseudocyst is a convenient shorthand rather than a histological rule. Treat both as extravasation phenomena unless pathology says otherwise.

	Simple (oral, sublingual) ranula	Plunging (diving, cervical) ranula
Compartment	Sublingual space only, above the mylohyoid muscle	Submandibular space, with or without a residual sublingual component
Route	Does not cross the mylohyoid sling	Through a defect in the mylohyoid muscle in about 88 percent, around its posterior free edge in about 12 percent
Clinical appearance	Bluish, translucent swelling in the floor of the mouth, often unilateral and paramedian	Painless soft submandibular or upper cervical mass, frequently with nothing visible in the mouth
Relative frequency	About 82 percent of ranulas	About 18 percent of ranulas
Histology	Extravasation pseudocyst in most; retention cyst in the minority	Extravasation pseudocyst, essentially always
Shape on CT	Lenticular when unilateral, horseshoe-shaped when it crosses the midline	Larger and more irregular, comet or teardrop shaped with the bulk below the mylohyoid
Relation to submandibular gland	Not applicable	Sits medial and anterior to the gland and displaces it laterally and posteriorly
Definitive operation	Transoral excision of the sublingual gland	Transoral excision of the sublingual gland, with simple drainage of the cervical collection

Simple versus plunging ranula. The mylohyoid muscle is the dividing line.

The anatomy that makes a ranula plunge

The mylohyoid muscle is the floor of the mouth. It slings from the mylohyoid line of the mandible to the hyoid bone and separates the sublingual space above it from the submandibular space below and lateral to it. The sublingual space is bounded anteriorly by the mandible, medially by the genioglossus and geniohyoid complex, inferolaterally by the mylohyoid and superomedially by the mucosa of the floor of the mouth. It contains the sublingual gland and duct, the deep part of the submandibular gland and Wharton duct, the lingual artery and vein, the lingual nerve and branches of cranial nerves IX and XII. Right and left sublingual spaces communicate anteriorly under the frenulum, which is why some ranulas are horseshoe-shaped.

The two spaces are continuous around the posterior free margin of the mylohyoid, and that was the traditional explanation for how a ranula plunges. It is not the usual route. The mylohyoid is commonly deficient: a fissure or oval opening, the mylohyoid boutonniere, through which sublingual gland and fat herniate. Nathan and Luchansky found such a deficiency in 82 of 300 dissected half-heads (27.3 percent), bilateral in 11.3 percent of cadavers. Harrison and colleagues found a hiatus with an associated hernia in 10 of 23 cadavers, and the hernia contained sublingual gland in 9 of them, which is the anatomical argument for taking out the sublingual gland rather than the submandibular gland.

Lee and colleagues then showed the same thing on CT in 41 plunging ranulas. Thirty-six (88 percent) took the anterior shortcut directly through a mylohyoid defect, most often in the anterior third of the muscle, and the sublingual gland was partly herniated through the defect in 30 of them. Only 5 (12 percent) travelled around the posterior free edge. The submandibular space was involved in every single case.

Annotated CT of a ranula showing the sublingual space, mylohyoid muscle and submandibular gland — The same study with overlays. Orientating yourself to the mylohyoid muscle is the whole diagnosis: above it is the sublingual space, below and lateral to it is the submandibular space. Credit: Dr. Disha Lokhandwala

Ranula on ultrasound, CT and MRI

Start with ultrasound. In the largest series, 207 ranulas scanned over 20 years, the lesion was hypoechoic to anechoic in 97.6 percent, was always in close relationship to the sublingual gland and the mylohyoid muscle, and ultrasound depicted the exact plunging pattern in every plunging lesion. Palpating the floor of the mouth and the submandibular region while scanning, described as sonopalpation, has been reported to make the relationship between the sublingual gland, the fluid and the mylohyoid dehiscence easier to see, although only in a three-patient proof-of-concept series. Ultrasound will not reach a large retropharyngeal or parapharyngeal extension, so cross-sectional imaging follows when the lesion is big, recurrent or preoperative.

Modality	Simple ranula	Plunging ranula	Infected ranula
Ultrasound	Thin-walled anechoic or hypoechoic collection in the sublingual space, in contact with the sublingual gland, no internal vascularity	Irregular collection extending below the level of the mylohyoid; the defect and the herniated gland can usually be shown directly	Thickened wall, internal echoes and debris, increased peripheral flow
CT (contrast-enhanced)	Well-defined unilocular low-attenuation cyst, lenticular if unilateral and horseshoe-shaped if it crosses the midline, thin or no wall enhancement	Comet or teardrop-shaped collection filling the submandibular space, displacing the submandibular gland laterally, with or without a tail back into the sublingual space	Thick enhancing wall, higher attenuation contents, adjacent fat stranding
MRI	T1 hypointense to intermediate (signal rises with protein content), T2 hyperintense, thin non-enhancing wall, no restricted diffusion	Coronal and axial T2 fat-suppressed images show the tail and the exact level of the mylohyoid best	Higher T1 signal, T2 heterogeneity, thick enhancing wall, surrounding oedema
Diffusion-weighted imaging	No restricted diffusion. This is what separates a ranula from an epidermoid cyst, which restricts	Same	May restrict because of pus, so interpret with the wall enhancement

Imaging appearance of a ranula by modality.

The tail sign, and how far to trust it

When a ranula herniates, the part left behind in the sublingual space is squeezed into a thin band that points back towards the sublingual gland. That band is the tail sign, and the whole lesion is then described as comet-shaped, with the body in the submandibular space and the tail in the sublingual space. Finding it is close to diagnostic, because it tells you the collection came from above the mylohyoid and therefore from the sublingual gland.

A tail you cannot see, though, proves nothing. In the Lee CT series the tail sign was present in only 14 of 41 plunging ranulas, about a third: in the remaining 22 lesions that went through a mylohyoid defect, the sublingual component had emptied completely into the neck and left no tail behind. Reporting a submandibular cystic mass as “not a ranula because there is no tail sign” is therefore a mistake. Look instead for the mylohyoid defect itself, the herniated sublingual gland and the absence of a normal fat plane between the collection and the gland.

Reporting checklist

Compartment: sublingual space only, or does the collection cross the level of the mylohyoid muscle.
Route, if it crosses: through a mylohyoid defect (name the third of the muscle) or around the posterior free margin.
Sublingual gland: normal, partly herniated through the defect, or effaced by the collection. Say which side.
Tail sign: present or absent. State that its absence does not exclude a plunging ranula.
Submandibular gland: displaced but normal, versus intrinsically abnormal, and state the direction of displacement.
Extent: parapharyngeal, retropharyngeal, tongue base, vallecula or infrahyoid extension, and the distance from the airway.
Complicating features: wall thickening, enhancement, internal debris, surrounding fat stranding, or airway narrowing.
Alternatives considered and why they are out: restricted diffusion would favour an epidermoid, fat globules a dermoid, septations and fluid-fluid levels a lymphatic malformation, a calculus or a dilated Wharton duct submandibular obstruction.

Differential diagnosis of a cystic mass in the floor of the mouth

Lesion	What tells it apart	Compartment
Epidermoid cyst	Restricted diffusion on DWI with low ADC. On CT and ultrasound it can be identical to a ranula, so DWI is the discriminator	Floor of mouth, often midline
Dermoid cyst	Fat globules floating in fluid, the sack of marbles appearance; fat attenuation on CT and high T1 signal	Midline floor of mouth, submental
Lymphatic malformation	Multiloculated and septated, fluid-fluid levels, insinuates across compartments rather than respecting one, thin peripheral enhancement	Trans-spatial
Second branchial cleft cyst	Centred at the angle of the mandible along the anterior border of sternocleidomastoid, posterolateral to the submandibular gland, no relationship to the sublingual gland and no tail	Posterior submandibular space and carotid space
Thyroglossal duct cyst	Midline or paramedian, embedded in or abutting the strap muscles, at or below the hyoid, tract towards the foramen caecum	Midline, infrahyoid more often than suprahyoid
Submandibular sialadenitis with obstruction	The gland itself is enlarged and enhancing, with a calculus and a dilated Wharton duct; the fluid is intraglandular or ductal, not a separate walled-off collection	Submandibular gland and duct
Abscess (including Ludwig angina)	Thick enhancing rim, restricted diffusion, gas, fat stranding, systemic sepsis and pain. A ranula can become infected and look like this	Sublingual, submandibular, often bilateral
Venous or venolymphatic malformation	Phleboliths, gradual filling on delayed images, changes with Valsalva or position	Trans-spatial
Cystic or necrotic node, cystic metastasis	Nodal location with a thick irregular wall; look for a primary in the oropharynx or thyroid	Submandibular, level I to II
Simple lingual or floor-of-mouth mucocele	Much smaller, superficial and submucosal, arising from a minor salivary gland rather than the sublingual gland; no relationship to the mylohyoid	Submucosal, floor of mouth or ventral tongue

Cystic floor-of-mouth lesions and the single feature that separates each from a ranula.

Clinical features and who gets a ranula

Simple ranula: a painless bluish translucent swelling in the floor of the mouth. Large lesions push the tongue up and interfere with speech, chewing and denture fit.
Plunging ranula: a soft, painless, non-tender submandibular or upper cervical swelling. The floor of the mouth is often completely normal, which is exactly why these are sent for imaging as an undiagnosed neck mass.
Age and sex: most present in the second and third decades. In one series of 20 plunging ranulas the median age was 31 with 11 men and 9 women. Congenital cases occur but are rare.
Trauma: a clear history of blunt injury to the floor of the mouth or neck, or of dental or oral surgery, is present in a minority. Ranulas are also reported as a late complication of tongue cancer resection.
Ethnicity: plunging ranulas are markedly over-represented in Maori and Pacific Island Polynesian populations. Whether this reflects a higher rate of mylohyoid dehiscence is unknown.
Aspirate: viscous, straw-coloured, amylase-rich and protein-rich mucus. An amylase-rich aspirate from a submandibular cystic mass is strong supporting evidence, but it is not treatment.
Malignant potential: none. A ranula does not transform.

What the surgeon does with your report

Every treatment for a ranula is an attempt to stop saliva escaping from the sublingual gland. They differ in how completely they achieve that, and the recurrence figures follow directly. The most recent systematic review, 71 studies and 809 patients, found that excision including the ipsilateral sublingual gland kept recurrence below 10 percent, while anything that left the gland behind ran at 15 to 30 percent. Most recurrences declare themselves within 3 to 6 months.

Treatment	What it does	Reported recurrence	Comment
Transoral excision of the sublingual gland	Removes the source of the leak	Under 10 percent	The reference treatment for both oral and plunging ranula. Complete excision beat partial excision 0 of 22 versus 5 of 20 in a comparative series
Transcervical excision	Removes the cervical collection, with or without the gland	Similar cure rate to the transoral route when the gland is taken	Higher morbidity than transoral in pooled data; lingual nerve injury is the main risk
Excision of the cyst without the gland	Removes the wall, not the source	15 to 30 percent	Illogical for a pseudocyst and the numbers show it
Marsupialisation	Creates a drainage tract into the mouth	15 to 30 percent	Simple and low-morbidity; micromarsupialisation performs better than classical marsupialisation in pooled series
Bleomycin sclerotherapy	Induces fibrosis and seals the leak	3 to 10 percent	The best-performing sclerosant in the pooled data
OK-432 (picibanil) sclerotherapy	Immune-mediated sclerosis	Good for oral lesions, over 50 percent for plunging lesions	In a randomised placebo-controlled trial every intraoral ranula resolved completely but only 1 of 4 plunging ranulas did
Polidocanol foam sclerotherapy	Detergent sclerosant, low toxicity	4 of 34 unfavourable outcomes, so about 88 percent complete resolution	Newer option for sublingual ranula; larger lesions did worse
Aspiration alone	Removes the fluid only	Highest of all	Diagnostic at best. Not a treatment

Treatment of ranula and reported recurrence. Note that a 2025 network meta-analysis of 18 non-randomised studies found the certainty of this evidence low to very low, so no single option is proven superior.

Read that last line carefully before you write a management sentence into a report. The direction of travel in the literature is consistent, and sublingual gland excision is the defensible default, but the evidence base is retrospective and no randomised comparison of the surgical options exists. Describe the anatomy precisely and leave the choice of operation to the surgeon.

Why it is called a ranula

“Ranula” is the diminutive of the Latin rana, a frog. The bluish translucent bulge lifting the mucosa of the floor of the mouth was thought to resemble the inflated vocal sac of a frog. The synonyms follow the anatomy rather than the amphibian: oral or sublingual ranula for the lesion confined above the mylohyoid, and plunging, diving or cervical ranula for the one that reaches the neck.

Ranula CT and clinical appearance compared with the inflated vocal sac of a frog — Why the name. The translucent bulge in the floor of the mouth was thought to look like the inflated vocal sac of a frog, and “ranula” is the diminutive of the Latin “rana”, a frog.

Frequently asked questions

What is a ranula?

A ranula is a collection of saliva in the floor of the mouth arising from the sublingual gland. In most cases the gland or its ducts have been disrupted and mucus has extravasated into the surrounding tissue, so the lesion is a pseudocyst with a wall of granulation and fibrous tissue and no epithelial lining. A true epithelium-lined retention cyst from simple ductal obstruction is the less common form. Ranulas are benign and do not become malignant.

What is the difference between a simple and a plunging ranula?

The mylohyoid muscle decides it. A simple, also called oral or sublingual, ranula stays in the sublingual space above the mylohyoid and presents as a bluish swelling in the floor of the mouth. A plunging, also called diving or cervical, ranula extends into the submandibular space below the muscle and presents as a painless neck lump, often with a completely normal mouth. About 82 percent of ranulas are oral and 18 percent plunging. Both are treated by removing the sublingual gland.

How does a ranula appear on CT?

As a well-defined, thin-walled, unilocular cyst of fluid attenuation with little or no wall enhancement. A unilateral simple ranula is lenticular; one that crosses the midline under the frenulum is horseshoe-shaped. A plunging ranula is a larger comet or teardrop-shaped collection filling the submandibular space and displacing the submandibular gland laterally and posteriorly. Wall thickening, higher-attenuation contents and adjacent fat stranding indicate infection.

What is the tail sign of a ranula?

The tail sign is the thin collapsed band of the collection left behind in the sublingual space after the rest of it has herniated into the neck, so the whole lesion looks like a comet with its body below the mylohyoid and its tail above. It confirms a sublingual origin when you see it, but it is not sensitive: in the largest CT series it was present in only 14 of 41 plunging ranulas. Its absence does not exclude the diagnosis.

How does a ranula look on ultrasound?

Anechoic or hypoechoic with a thin wall, no internal vascularity, and always in contact with the sublingual gland and the mylohyoid muscle. In a series of 207 ranulas the lesion was hypoechoic to anechoic in 97.6 percent, and ultrasound showed the exact plunging pattern in every plunging lesion. Compression during scanning, called sonopalpation, helps display the relationship between the gland, the fluid and the mylohyoid defect. Ultrasound is a reasonable first test.

What does a ranula look like on MRI?

A T2 hyperintense, T1 hypointense to intermediate collection with a thin non-enhancing wall. T1 signal rises as the protein content of the mucus rises, so an intermediate T1 signal does not argue against the diagnosis. Fat-suppressed T2 images in the axial and coronal planes show the tail and the exact level of the mylohyoid best. A ranula shows no restricted diffusion.

How do you tell a ranula from an epidermoid cyst?

Diffusion-weighted imaging. On CT and on ultrasound the two can be indistinguishable, but an epidermoid cyst restricts diffusion with a low ADC while a ranula does not. A dermoid cyst is separated by its fat globules and the sack of marbles appearance, and a lymphatic malformation by its septations, fluid-fluid levels and trans-spatial spread.

What is the best treatment for a ranula?

Transoral excision of the sublingual gland is the reference treatment for both oral and plunging ranulas, because it removes the source of the leaking saliva. A systematic review of 71 studies and 809 patients found recurrence below 10 percent when the ipsilateral sublingual gland was removed, against 15 to 30 percent when it was left in place. Complete excision of the gland beat partial excision in a comparative series, with no recurrence in 22 patients versus 5 of 20. A 2025 network meta-analysis nonetheless rated the overall certainty of evidence low to very low, so the choice is a surgical judgement.

Does sclerotherapy work for a ranula?

It depends on the agent and on whether the lesion plunges. In a randomised double-blind placebo-controlled trial of OK-432 every intraoral ranula responded completely but only 1 of 4 plunging ranulas did, and pooled data put OK-432 recurrence in plunging lesions above 50 percent. Bleomycin performs better at 3 to 10 percent, and a 2026 series of 34 sublingual ranulas treated with 3 percent polidocanol foam reported complete resolution in 30 of them. Sclerotherapy is a reasonable option for an oral ranula and a weak one for a plunging ranula.

Can a ranula go away on its own?

A small ranula that follows minor trauma can decompress spontaneously into the mouth and settle, and a period of observation is reasonable in a child with a small asymptomatic lesion. A ranula that persists, enlarges, interferes with speech or eating, or presents as a neck mass will not resolve without treating the sublingual gland, and aspiration alone has the highest recurrence rate of any intervention.

References

Single best review article

Patel S, Bhatt AA. Imaging of the sublingual and submandibular spaces. Insights Imaging. 2018;9(3):391-401. PMID: 29675626. Open access, and the best single account of the anatomy and the cystic differential.

Imaging and anatomy

Coit WE, Harnsberger HR, Osborn AG, Smoker WR, Stevens MH, Lufkin RB. Ranulas and their mimics: CT evaluation. Radiology. 1987;163(1):211-216. PMID: 3823437.
Lee JY, Lee HY, Kim HJ, et al. Plunging ranulas revisited: a CT study with emphasis on a defect of the mylohyoid muscle as the primary route of lesion propagation. Korean J Radiol. 2016;17(2):264-270. PMID: 26957912.
Koch M, Mantsopoulos K, Leibl V, Muller S, Iro H, Sievert M. Ultrasound in the diagnosis and differential diagnosis of enoral and plunging ranula: a detailed and comparative analysis. J Ultrasound. 2023;26(2):487-495. PMID: 36527568.
Molotkova E, Maley J, Hoffman H. Sonopalpation for ultrasound evaluation of plunging ranula. Ear Nose Throat J. 2025 Jul 28 (online ahead of print). PMID: 40719167.
Nathan H, Luchansky E. Sublingual gland herniation through the mylohyoid muscle. Oral Surg Oral Med Oral Pathol. 1985;59(1):21-23. PMID: 3856203.
Harrison JD, Kim A, Al-Ali S, Morton RP. Postmortem investigation of mylohyoid hiatus and hernia: aetiological factors of plunging ranula. Clin Anat. 2013;26(6):693-699. PMID: 23355334.

Pathogenesis, clinical series and treatment

Quick CA, Lowell SH. Ranula and the sublingual salivary glands. Arch Otolaryngol. 1977;103(7):397-400. PMID: 880105.
Davison MJ, Morton RP, McIvor NP. Plunging ranula: clinical observations. Head Neck. 1998;20(1):63-68. PMID: 9464954.
Nguyen K, Goodman E, Vibhute M, Blake L, Richter GT, Kompelli A. Systematic review and meta-analysis of the management and outcomes of recurrent ranulas. Oral Dis. 2026;32(7):1816-1827. PMID: 41841403.
Souza MRF, Goncalves MWA, Martins-Chaves RR, et al. Treatments to avoid ranula recurrence: a network meta-analysis. J Oral Pathol Med. 2025;54(10):934-943. PMID: 40921455.
Chung YS, Cho Y, Kim BH. Comparison of outcomes of treatment for ranula: a proportion meta-analysis. Br J Oral Maxillofac Surg. 2019;57(7):620-626. PMID: 31239229.
Roh JL. Transoral complete vs partial excision of the sublingual gland for plunging ranula. Otolaryngol Head Neck Surg. 2022;167(3):479-483. PMID: 34932413.
Wendt M, Papatziamos G, Munck-Wikland E, Marklund L. Sclerotherapy of ranulas with OK-432: a prospective, randomized, double-blinded placebo-controlled study. Acta Otolaryngol. 2021;141(5):531-536. PMID: 33775200.
Li K, Yang X, Yu C, Zheng J, Du G, Zhou Q. Clinical outcomes of polidocanol foam sclerotherapy in treatment of sublingual ranula. Int Dent J. 2026;76(3):109512. PMID: 41861582.
Gontarz M, Bargiel J, Gasiorowski K, et al. Surgical treatment of sublingual gland ranulas. Int Arch Otorhinolaryngol. 2023;27(2):e296-e301. PMID: 37125362.

Related reading on RadioGyan: benign lymphoepithelial cysts of the parotid gland for the other common cystic salivary lesion, the sack of marbles sign for the dermoid that sits in the same differential, and retropharyngeal versus parapharyngeal abscess for the deep neck spaces a large plunging ranula can reach.

Original case and illustrations: Dr. Disha Lokhandwala. Co-author: Dr. Mansi Sarmalkar. Reviewed, rewritten and expanded in 2026.

Ranula Radiology: Simple vs Plunging Ranula on Ultrasound, CT and MRI

Quiz

What is a ranula?

The anatomy that makes a ranula plunge