Co-existence of Congenital Epidermoid Cyst and Ranula in a Newborn. Report of a Unique Case.

Background: Congenital cystic swellings involving the floor of the mouth include various lesions such as developmental cysts (e.g., dermoid and epidermoid cysts), ranulas, vascular malformations etc. However, coexistence of such conditions, possibly with a cause-and-effect- relationship, is rare. 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.

Methods: A 6-month-old female infant was referred to an Oral Medicine Clinic in Athens, Greece on October 2019 for evaluation of a swelling at the floor of the mouth, first noticed by her paediatrician just after birth. Clinically, a yellowish "pearly" nodule in close association with the orifice of the left submandibular duct, posteriorly transitioning to a diffuse bluish cystic swelling of the left floor of the mouth was observed. With a provisional diagnosis of a dermoid cyst and/or ranula, a surgical excision was performed under general anaesthesia.

Results: Histopathologically, a well-defined, keratin-filled, cystic cavity lined by orthokeratinized stratified squamous epithelium was observed in the anterior aspect while posteriorly and in close proximity, a dilated salivary duct lined by cylindrical, cuboidal or pseudostratified epithelium was noted. A final diagnosis of an epidermoid cyst intimately associated with a mucus retention cyst (ranula) of the submandibular duct was rendered.

Conclusions: The coexistence of two cystic lesions in the floor of the mouth with features of epidermoid and mucous retention cyst, respectively, is rare and its pathogenesis intriguing, especially in a newborn.