A case of a dermoid cyst on the floor of the mouth

Dermoid cysts on the floor of the mouth are relatively rare. We report a 34-year-old man with a cyst on the floor of his mouth. CT and MRI revealed a 6cm × 5cm × 3.5cm cyst in the sublingual space. Ten ml of a viscous reservoir fluid was sucked out through fine needle aspiration and the preoperative diagnosis was a ranula. The cyst was surgically removed using an intraoral approach under general anesthesia, and was found to be a dermoid cyst, not a ranula. Histological diagnosis was also of a dermoid cyst. The characteristics of the non-uniform appearance of MRI T2 intensity imaging, compression and dilatation imaging, and puncture fluid are useful for the differential diagnosis of a dermoid cyst. The pre-operative diagnosis of and surgical approach used for this disease have been discussed.