A Giant Epidermoid Cyst in the Floor of Mouth Mimicking Ranula.

Dermoid cysts are benign ectodermal-derived epithelial cysts rarely found on the floor of the neck. They may be congenital or acquired. They comprise three histological variants according to their contents and include dermoid, epidermoid, and teratoma. Epidermoid cysts are lined by epithelium but do not contain skin appendages like hair follicles and sebaceous glands, as seen in dermoid cysts. Teratoma on the other hand contain mesodermal element. They reveal either a supra-myelohyiod or infra-myelohyiod floor-of-mouth location and can be clinically confused with various close differentials including infections, tumours, mucous extravasation phenomena, and embryonic abnormalities. A 28-year-old female presented with a complaint of painless large swelling beneath the chin. Computed tomography (CT) scan with contrast revealed a right para-median thick-walled cystic lesion located in the sublingual space. A plunging ranula was suspected on radiological assessment. Aspiration cytology revealed keratin-containing fluid and pointed towards a tentative diagnosis of dermoid/epidermoid cystic lesion. The mass lesion was explored via a transcutaneous neck approach. The final histopathological evaluation of the excised cystic lesion eventually confirmed a diagnosis of epidermoid cyst. Consider epidermoid cyst as a possible differential for any floor-of-mouth swelling. They can be clinically and radiologically confused with close differential including ranula, dentoalveolar cyst and lipoma. Aspiration cytology examination is sometimes helpful in equivocal cases. Cyst excision with histological examination allows for a confirmatory diagnosis and is possibly the only means of distinguishing between specific histological variants of dermoids.