Congenital cervical immature teratoma arising in the left lobe of the thyroid gland.

We report on a fetal autopsy case in which a congenital cervical immature teratoma was diagnosed. A 24-year-old Japanese woman had carried a male fetus that was aborted because of a cervical tumor at 20 weeks 5 days of gestation. The cervical tumor weighed 93 g and measured 7.5x5.5x5 cm. The soft tumor was encapsulated by a fibrous layer, was solid with small cysts on the cut surface, and showed a brain-like appearance. The tumor was composed of neoplastic cells derived from the three germ cell layers: ectoderm, mesoderm, and endoderm. The cells showed both immature and mature features. Small areas of thyroid tissue were detected in the cervical tumor. The left lobe of the thyroid gland was not observed, but the right lobe of the thyroid gland was present laterally between the trachea and the esophagus. Therefore, we concluded that the cervical tumor had arisen in the left lobe of the thyroid gland rather than from the soft tissue of the neck.