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Ranula

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CT image of a simple ranula

Quiz

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

  1. Can undergo malignant transformation 
  2. Most commonly congenital in etiology. 
  3. Mucus retention cyst of sublingual or minor salivary glands
  4. Cyst aspiration is the treatment of choice.
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Answer: Mucus retention cyst of sublingual or minor salivary glands. Read the article below to find out why the other choices are incorrect.

Pathophysiology

  • Benign, mucous retention cyst arising from an obstructed sublingual or minor salivary glands in the sublingual space. 
  • Can be true cysts occurring due to ductal obstruction OR a pseudocyst resulting from ductal injury leading to extravasation and accumulation of saliva in the surrounding tissues.
  • Commonly acquired and rarely congenital.

Classification System : 

Ranulas are classified based on the extent of the lesion,

  • Simple: confined to sublingual space. True cyst. 
  • Diving, AKA plunging ranula: herniated either around or through the mylohyoid muscle extending into the submandibular space. Pseudocyst. 

Key Imaging Features 

CT Ranula Image with illustrations. Credit: Dr. Disha Lokhandwala

1. CT

1) Simple ranula- well-defined, thin-walled, unilocular, low-density cystic lesion with linear or no wall enhancement on postcontrast. Unilateral lesions appear as lenticular shapes and bilateral as horseshoe shape lesions. 

2) Diving ranula- 

Comet-tail morphology:

Tail sign- Collapsed sublingual portion of the cyst. All diving ranulas arise from the sublingual glands, which are seen as an extension of a small tail into the sublingual space. Lesion morphology is similar to a simple ranula with a tail in the anterior sublingual space and a body in the submandibular space medial to the submandibular gland.  

3)Infected ranula-thick enhancing walls with adjacent fat stranding and content may show increased attenuation.

2. MRI  

Well-defined cystic lesion with fluid signal intensity showing T1 hypointense and T2 hyperintense signal and a linear or non-enhancing wall on post-contrast studies if not infected. Altered T1/T2 signal with a thickened enhancing wall in the infectious lesion. T2 fat-suppressed sequence best delineates the tail sign of diving ranula. 

3. USG 

Thin-walled, hypoechoic cystic lesions in sublingual space. In case of infection, the walls appear thicker and have echogenic fluid content. 

Imaging Recommendation : 

Contrast-enhanced CT scan is the imaging modality of choice for the extension and characterization of the lesion. 

Top 3 Differential Diagnosis : 

1. Lymphatic malformation: Multilocular, septated lesion containing fluid-fluid levels and peripheral wall enhancement. 

2. Dermoid and epidermoid: Low-density lesion with a thin non-enhancing wall. Fat density on CT and high signal on T1 MRI in dermoid and diffusion restriction on MRI in epidermoid. 

3. Second branchial cleft cyst: Second branchial cyst can occur anywhere along the course of the second branchial apparatus, from the pharyngeal wall to the skin. The angle of the mandible is a common location. No tail sign. Branchial cysts tend to displace submandibular glands anteriorly, unlike the ranula, which displaces the submandibular gland laterally. 

Clinical Features : 

  • Symptoms: simple ranula presents as painless swelling in the floor of the mouth, while diving ranula presents as submandibular mass displacing the submandibular gland,
  • Age/Sex predilection: median age-30 years, slight male predilection. 
  • Risk factors: a history of neck or oral cavity trauma

Etymology  and synonyms :  

Ranula derives from the Latin word “Rana” meaning frog, from the resemblance of the lesion to the sublingual blebs in a frog’s mouth.  

Ranula CT and clinical appearance and comparison with a frog's vocal sac
Ranula CT and clinical appearance and comparison with a frog’s vocal sac

Treatment : 

  • Complete resection of the ranula with the obstructed sublingual gland to prevent a recurrence.
  • Sclerotherapy with OK-432 and bleomycin
  • Cyst aspiration has the highest recurrence rate. 

References: 

Single best reference article: 

Diagnostic Imaging: Head and Neck by Bernadette L Koch MD, Bronwyn E. Hamilton MD, Patricia A. Hudgins MD FACR, H. Ric Harnsberger MD. Elsevier publications  – Third edition. 

Other references: Coit WE, Harnsberger HR, Osborn AG, Smoker WR, Stevens MH, Lufkin RB. Ranulas and their mimics: CT evaluation. Radiology. 1987;163(1):211-216. doi:10.1148/radiology.163.1.3823437

“Vocal Sac.” Wikipedia, Wikimedia Foundation, 8 Dec. 2022, en.wikipedia.org/wiki/Vocal_sac. Accessed 20 Jan. 2023.

“Ranula.” Wikipedia, Wikimedia Foundation, 28 Dec. 2020, en.wikipedia.org/wiki/Ranula. Accessed 20 Jan. 2023.

Co-Authors: Dr. Mansi Sarmalkar.

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