Matured mediastinal teratoma extending into the cervical neck of an adult.

Teratomas have been reported to occur in various sites and organs. Cervical neck teratomas are relatively rare in adulthood, and mediastinal teratomas that extend into the cervical neck are also rare. Therefore, we report a case of a matured teratoma found in the cervical tumor of an adult. A 27-year-old woman was admitted with a cervical soft tumor. Preoperative examination revealed a cystic mass in the upper mediastinum that extended to the thyroid. We diagnosed this as a thymic or foregut cyst and removed the tumor via a collar incision. Histological examination revealed a benign mature teratoma.