A case of congenital plunging ranula

A 10-day-old newborn presented with swelling in the floor of the mouth since birth, which led to difficulty in swallowing. On examination, a soft, smooth surface, cystic, pale blue in colour, non-pulsatile swelling in the floor of the mouth in sublingual and left submandibular space, appeared to displace the tongue superiorly.

MRI revealed a well-defined, homogeneous, thin-walled, T2 hyperintense fluid-filled cystic lesion, with internal septa in the sublingual and bilateral submandibular space. No e/o solid component was seen. It appears mildly hyperintense on T1WI p/o proteinaceous content. No evidence of diffusion restriction or blooming on SWI images was seen.

The maximum dimensions of the lesion measured approximately: 35 x 40 x 22 mm (AP x TR x CC). Superiorly, the lesion closely abuts the inferior surface of the tongue with loss of fat plane and the possibility of adherence/involvement to the tongue. Posteriorly, the lesion appears to extend into bilateral submandibular space (left > right ) and left retromolar region from the posterior margin of the mylohyoid muscle. From imaging findings, congenital plunging ranula, and lymphatic malformation were considered differentials.

A ranula is a cyst that develops in the floor of the mouth. It occurs when the sublingual gland’s duct becomes blocked (due to atresia, osteal adhesion or trauma), causing proximal expansion and mucous retention cysts, seen in neonates lined by salivary duct epithelium or disruption of minor salivary ducts leading to extravasation of mucous in adjacent structures (not lined by epithelium). Ranulas are classified into two types: (1) simple ranulas, which are confined to the sublingual space, and (2) plunging ranulas, which extend around the mylohyoid into the submandibular neck space. Congenital ranulas are rare, with an incidence of less than 1%. They typically do not cause symptoms and may resolve naturally. However, in this case, the patient presented with a large and symptomatic congenital ranula [1].

Generally, the diagnosis of congenital ranula is based more on clinical examination, typically in which the patient presents with swelling in the floor of the mouth since birth with or without feeding difficulty. A large ranula can complicate and cause compression over the trachea or can undergo rupture.

USG, CT and MRI can be helpful in determining the size and the location of the lesion. On USG, it appears as a fluid-filled cystic lesion in the floor of the mouth and often shows internal echoes within due to mucinous content. MRI scan is considered a gold standard as it gives high-resolution images and determines the precise size, location, content and extension of the lesion, providing precise information for better planning of the surgical approach. On MRI, plunging ranulas are demonstrated by hypo or hyperintensity on T1-weighted images and by hyperintensity on T2-weighted and STIR images. Usually, there is no postcontrast enhancement; however, enhancement of the capsule may be seen, if there is a secondary infection. The “tail sign” is a distinctive feature of plunging ranulas. It appears as a smooth, teardrop-shaped fluid-filled cyst with a narrow part extending into the sublingual space and a wider part extending into the submandibular space. This sign is caused by saliva leaking from the sublingual gland and flowing under the mylohyoid muscle [2].

Ranulas can spontaneously resolve. So, if there are no clinical issues, a wait-and-see approach can also be considered. However, a large plunging ranula can be treated by removing the sublingual salivary gland on the affected side, which is the cause of the condition. The fluid-filled cyst in the neck should also be drained through the mouth [3]. Other treatment options include marsupialisation, cryotherapy, sclerotherapy, or laser excision. Complications may occur after surgical treatment of a plunging ranula, which may include recurrence of the ranula, infection, injury to adjacent structures, and nerve injury, which may warrant further radiological investigations.

Owing to the large size of the ranula, our patient was surgically managed by excision of the sublingual salivary gland on the affected side and was kept on follow-up.

A midline cystic swelling in a newborn should always raise a suspicion of plunging ranula. MRI should be considered before surgical planning to provide accurate diagnosis and greater delineation of surgical planes.