Congenital cystic lesions involving the floor of the mouth are rare entities encompassing a broad spectrum of pathoses, including developmental cysts (e.g. dermoid/epidermoid cysts), ranulas, vascular malformations etc. In a recent systematic review by Lucas et al. [1], out of 65 studies involving 85 patients with congenital lesions of the floor of the mouth, the most common lesion was dermoid cyst, followed by foregut duplication cyst, ranula, epidermoid cyst, and heterotopic gastrointestinal cyst.

Dermoid/epidermoid cysts are usually diagnosed in children or young adults, either incidentally or due to associated signs and symptoms, while presentation in infants is a more infrequent phenomenon [2,3]. Rarely, such cystic lesions may coincide with or facilitate the development of cyst-like dilation of salivary ducts or other reactive lesions such as mucoceles/ranulas, possessing diagnostic pitfalls.

The purpose of this case report is to present a rare case of a congenital epidermoid cyst associated with a mucous retention cyst in a newborn.

A 6 month-old Caucasian, full term female infant in good general health was referred to an Oral Medicine Clinic in Athens, Greece, on October 2019 for evaluation of a ‘pearly’ yellowish swelling located in the midline of the floor of the mouth. The lesion was first noticed by her paediatrician just after birth, slowly enlarging since then according to her mother. Clinical examination revealed a soft, fluctuating, non-pedunculated, yellowish nodule covered by normal mucosa with a prominent vasculature (Figure 1A), in close association with the orifice of the left submandibular duct (Figure 1B), posteriorly transitioning to a diffuse bluish cystic swelling (Figure 1C). The rest of the oral cavity was within normal limits and no lymphadenopathy or other extraoral findings were detected. Ultrasound evaluation revealed an irregularly shaped cystic lesion with a maximum diameter of 5 mm and maximum craniocaudal lenght of 13 mm (Figure 2A, 2B). With a provisional diagnosis of a dermoid cyst and/or mucous cyst, surgical excision was performed under general anaesthesia. Intraoperatively, a round cystic lesion was identified anteriorly and in continuity with a second more diffuse cystic lesion. The latter exhibited a significant posterior extension towards the submandibular gland as an elongated cylindrical dilatation (Figure 3).

In summary, an oval shaped cystic nodule containing whitish creamy material was observed in the anterior aspect of the surgical specimen, transitioning posteriorly to another cystic lesion (Figure 4). Histopathologic examination revealed two cystic spaces in close proximity, both showing epithelial lining (Figure 5A). The anterior lesion was a large, well-delineated, keratin-filled, cystic cavity lined by orthokeratinized stratified squamous epithelium with absence of dermal appendages in the fibrous cystic wall (Figure 5B), while posteriorly, a dilated salivary duct lined by single columnar, cuboidal or pseudostratified epithelium, partially containing amorphous eosinophilic material, was observed (Figure 5C). Multiple lobules of seromucinous minor salivary glands were also noted in the surrounding area. Taking into consideration the clinical and histopathological findings, a final diagnosis of an epidermoid cyst intimately associated with a mucous retention cyst of the submandibular duct was rendered. The postoperative course was uneventful with complete healing and 2 years postoperatively the patient remains free of any symptoms, while there has been no evidence of recurrence.

Dermoid/epidermoid cysts are rare developmental lesions considered as cystic forms of teratoma, with about 6.5% of them involving the head and neck region and 1.6% found in the oral cavity, accounting for less than 0.01% of all intraoral cystic processes [2,4]. They predominantly present at the midline of the floor of the mouth in children and young adults, while approximately 15% of them are congenital, although even then, diagnosis is usually rendered during the second and third decades of life, when cysts are large enough to become clinically evident [4,5]. These lesions are extremely rare in neonates and only about 30 cases of congenital epidermoid cysts of the floor of the mouth have been reported in infants so far [2,4-6].

Depending on whether these cysts are located above or inferiorly to the geniohyoid muscle, they may appear either as painless, yellowish, intraoral nodules with a rubbery texture or as submental swellings respectively. They usually show an indolent clinical course but when intraoral and of a considerable size, they may lead to serious complications such as tongue displacement with associated dysphagia, dysphonia, and even obstruction of the airway [4]. Both types of cysts are lined by an epidermis-like epithelium, with the dermoid type also showing dermal appendages (e.g. sebaceous and/or sweat glands, hair follicles) in the cystic wall [5]. Treatment of choice is surgical excision with a good prognosis and a low relapse rate [7,8].

Ranulas are most commonly acquired mucus cysts appearing either as asymptomatic bluish swellings off-midline in the floor of the mouth (simple ranula) or as plunging masses in the submandibular or submental area [9]. They are caused either by trauma resulting in a mucus extravasation cyst or by obstruction of a salivary duct (mucus retention cyst), the latter presenting histopathologically as a cystic cavity lined by 1 to 2 layers of cuboidal or columnar epithelium. Congenital ranulas are observed in about 0.74% of newborn infants and they are thought to result from congenital atresia of the salivary duct orifices of Bartholin’s or Warthon’s duct. Rarely and when large enough, ranulas may cause tongue displacement, feeding difficulties or even airway obstruction [9,10].

In paediatric population, intraoral dermoid/epidermoid cysts may clinically masquerade as mucous cysts [11]. However, multi-focality or coexistence with other congenital or reactive cystic lesions is extremely rare, with only sparse cases of epidermoid cysts co-existing with other intraoral developmental cysts reported in the literature so far such as with heterotopic gastrointestinal cyst [12], oral alimentary tract cyst [13], thyroglossal duct cyst [14], and in one case with two dermoid cysts. [6] To the best of our knowledge, the concomitant presence of an epidermoid and a mucous retention cyst has never been described before, with the exception of a concurrent extravasation mucocele and an epidermoid cyst of the lower lip reported in a 13-year-old boy [15].

The pathogenetic mechanism resulting in the concurrence of these two cystic lesions in the floor of the mouth is intriguing, especially in a newborn. Theoretically, the coexistence of these two lesions could be coincidental. Nevertheless, although the ranula in our case could also be congenital, there has been no recurrence that could suggest congenital atresia of the Wharton’s duct, suggesting that its nature was rather reactive. A more reasonable explanation would be that a slowly growing congenital epidermoid cyst, incidentally developing adjacent to the submandibular duct orifice, could cause obstruction of the duct tract and a secondary mucous retention phenomenon.

The development of congenital cystic lesions in the floor of the mouth is uncommon, but the coexistence of more than one of these entities, possibly with a cause and effect relationship, is extremely rare. Increased awareness of these lesions by obstetricians and neonatologists is mandatory, since prenatal diagnosis of these lesions enables proper management and avoidance of complications such as respiratory compromise during delivery.