Ectopic Salivary Gland Cyst in the Neck: Association with Congenital Plunging Ranula.

Congenital ranula is rare. We report a large, symptomatic, congenital plunging ranula associated with a salivary gland cyst in the neck. To the best of our knowledge, this is the first such reported case. Even though both the cysts had their origin from the sublingual gland, only the cervical cyst had a capsular covering. Herniation of a part of the immature sublingual gland anlage through a congenital mylohyoid defect, its separation, and subsequent maturation could explain this occurrence.

INTRODUCTION

Congenital ranula is rare, frequently small, and asymptomatic at birth. A plunging congenital ranula is even more infrequent. We report the case of a large, plunging ranula associated with an ectopic salivary gland cyst in the neck of a newborn. Such a case has not been reported yet. Also discussed, is the possible mechanism of its occurrence.

CASE REPORT

A 5-day-old male baby was referred to our hospital with a large oral swelling and difficulty in breastfeeding. On examination, there was a large tense, sublingual cystic swelling on the left side. It had lifted the tongue upward, backward, and to the right and produced a bulge in the submental and left submandibular region, which was confirmed on bimanual palpation. Another cystic swelling was present in the region of the left anterior triangle, which became more apparent when the child cried. Neither cross fluctuations nor any fluid shift could be elicited across the intraoral and the cervical swelling. The oral swelling was aspirated at birth in the previous center, but it had recurred rapidly to its present size. A possibility of plunging ranula/lymphangioma was kept.

The child was started on nasogastric feeds. His hematological and biochemical parameters were normal. Computed tomography (CT) scan revealed two large unilocular, homogenous cystic swellings. The oral swelling was noncapsulated, occupied most of the sublingual space with a retromandibular extension. The cervical swelling was in the subcutaneous plane, anterolateral, and to the left of larynx and trachea, capsulated and had no apparent communication with the oral swelling in either the sagittal or in axial view [Figure 1]. Considering the size and location of the two swellings, child's inability to breastfeed and history of recurrence following aspiration, excision was planned. Excision was commenced through the intraoral approach by incising the mucosa overlying the cyst. The cyst was carefully dissected from the mucosa and undersurface of the tongue avoiding the lingual vessels, nerves medially. The submandibular duct was cannulated at the outset with a 24 Gauge intravenous cannula as a safeguard against injury. The dissection was continued up to the level of floor of the mouth. Ipsilateral mylohyoid muscle was indistinct and stretched out by the cyst. To have a good access of superficial part of submandibular gland and in anticipation of any small communication between the two cysts that might have been missed at clinical examination and CT scan, it was decided thereupon to halt the oral dissection and commence dissection of the cervical cyst and traverse proximally to access the submandibular space. However, the cervical cyst was found to be independent of the oral swelling. The remaining oral dissection was then completed and the cyst excised. The use of magnification loupes was very helpful in delineating the small anatomical structures of neonate. We also used a muscle stimulator to protect the muscles of the tongue and floor of the mouth.

Figure 1

(a) Computed tomography scan (sagittal view) showing a large homogenous, unilocular, oral cyst, and a cervical cyst. It has lifted the tongue (black star) superiorly and posteriorly which is abutting the hard palate. The cervical cyst has a capsule (white arrow head) and does not communicate with the oral cyst. (b) Computed tomography scan (axial view). Oral cyst is a plunging ranula occupying both the sublingual and submandibular space with no communication with the cervical cyst

Grossly, the cervical cyst was capsulated while the oral cyst was devoid of a capsule. Both cysts were filled with mucoid fluid. Postoperative period was uneventful. Breastfeeding was started on the 3rd postoperative day and he was discharged on day 8. Presently, he is thriving well. Histology revealed that both the cysts were lined by stratified squamous and columnar epithelium with an intact basement membrane. The subepithelial layers exhibited fibromuscular tissue, dense chronic inflammatory infiltrate, congested, and dilated blood vessels. In addition to the oral cyst, the cervical cyst too demonstrated the salivary gland tissue [Figure 2].

Figure 2

The cervical cyst showing stratified columnar epithelial lining (white arrow). Also seen is salivary gland tissue (black star) (H and E)

DISCUSSION

Ranula (a mucocele arising from the sublingual gland) is seldom reported as a congenital lesion and if present is of the simple type (confined to the sublingual space superficial to the mylohyoid muscle). A plunging ranula (mucus extravasation from sublingual gland and its collection in the submandibular space deep to the mylohyoid) is rarely seen at birth. Our child presented with a large, symptomatic plunging ranula at birth. It was a mixed type of plunging ranula (having both an oral and a submandibular component) as described by Zhao et al.[1] There was another cystic swelling in the neck. Child's inability to breastfeed, a recurrence following aspiration and a possibility of respiratory compromise prompted us for excision. No communication was elicited between either cysts clinically, radiologically, or at surgery. Moreover, both the cysts in our patient were filled with clear mucoid fluid. Considering the fact that mucus production in oral cavity is limited to the sublingual and minor salivary glands and the oral cyst in our case was occupying both the sublingual and submandibular spaces, establishes it as a plunging ranula arising from the sublingual gland. Histologically, both the cysts had an epithelial lining with an intact basement membrane, a subepithelial tissue with dense chronic inflammatory infiltrate, congested, and dilated blood vessels, which is a characteristic of ranula.[12] The occurrence of a congenital plunging ranula and its association with an ectopic salivary gland cyst in the neck is unique to our case and has not been previously reported.

The etiology and pathophysiology of congenital ranula are not clear and is said to be due either to ductal atresia or acinus dilatation.[3] On the other hand, plunging ranula is a type of extravasation cyst that is formed by rupture of the sublingual gland acini secondary to trauma or duct obstruction. The saliva either travels over the back of mylohyoid muscle or drains directly through the muscle to enter the submandibular space. In the latter case, it is speculated that a part of sublingual gland herniates through a preexisting hiatus in the mylohyoid muscle and gets constricted by it leading to its rupture with persistent extravasation of mucus from the ruptured acini.[45]

Gaps in mylohyoid muscle are reported in 10%–72% of cases at cadaveric dissections and in 77% CT studies performed in asymptomatic individuals.[6] Human embryo dissections have shown these gaps as early as 8 weeks of gestations.[7] The sublingual gland anlage also appears around this time.[8] In our case, it is possible that part of the early budding sublingual anlage herniated through a defect in the developing mylohyoid and the constricting effect of the muscle resulted in some of it getting separated. Since this tissue was immature (precanalised stage), constriction resulted in separation rather than rupture of acini which happens in a mature secreting gland. With foetal lengthening, the detached segment gravitated to the adjoining subcutaneous space in the neck. Subsequent maturation, canalization, and onset of secretory function resulted in the formation of a mucus filled, ectopic salivary cyst in the neck. The remaining unsequestrated, herniated sublingual anlage developed later as a cyst extending into the submandibular space (plunging ranula).

Normally, the sublingual gland (unlike other salivary glands) does not have a proper capsule or fascial sheath covering. This is believed to be due to the infiltration of the gland substance by the connective tissue in the sublingual space.[58] This may explain why in our case, the ectopic salivary cyst had a capsule (since it matured in the neck away from the sublingual area) while the oral cyst was devoid of capsule because it developed within its natural environment.

This case gives credence to the theory of herniation of a knuckle of sublingual gland through a hiatus in the mylohyoid muscle for the formation of a plunging ranula and that this process can also occur antenatally.

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