Mature cervical teratoma (MCT) is a germ cell tumor. The occurrence of teratoma in the neck region is rare in adulthood, accounting for only 3% of all teratomas.

We present the case of a 25-year-old woman with a left cervical mass. The diagnostic, therapeutic and follow-up process is described.

A 25-year-old woman patient was admitted to our hospital with a 2-month history of a progressively enlarging painless mass in the left neck, with no other associated symptoms. Physical examination revealed a stoney and immobile mass in the anteroinferior neck. Thyroid function tests, Alpha-feto-protein (AFP) and beta-human chorionic gonadotropin(β-HCG) were normal. Ultrasonography revealed a large oval heterogeneous mass, measuring 50 x 25 mm. Computed tomography also revealed a nonhomogeneous mass with fatty tissue, calcified nodes, and variably sized cysts, with well-defined margins. The lesion compressed the trachea and left lobe of the thyroid to the right anterior side and invaded into the anterior mediastinum. A FNA was performed with a diagnosis of mature cervical teratoma. Surgical treatment was indicated. An anterior cervicotomy was performed, an encapsulated mass was found, connected by a pedicle to the left thyroid lobe and by two pedicles to the anterior mediastinum. The patient did not show recurrence after almost 12 months of follow-up.

Early surgical excision is the treatment of choice in cases of MCT, and recurrence is rare once complete resection has been achieved. Clinicians should be aware of these cystic tumors in the cervical neck region extending into the mediastinum.