Immature teratoma of the mediastinum arising in ectopic thyroid tissue: a case report.

BACKGROUND: Papillary carcinoma can arise from ectopic thyroid tissue, but teratoma have not been described. Differentiation into thyroid follicles does not occur in mediastinal teratomas. CASE: A case of tipper mediastinal immature teratoma occurred in an 18-day-old male newborn. The histologic examination revealed the presence of a discontinuous rim of compressed thyroid follicles on the outer aspect of the tumor capsule. This finding is consistent with the origin of the teratoma in ectopic thyroid tissue, and it has not been previously described in the literature. The patient was free of disease after 22 months, in accordance with the benign behavior of immature teratoma in infancy. CONCLUSION: Ectopic thyroid tissue can undergo the same pathologic changes as the thyroid gland, including the rare occurrence of teratoma. (Anal Quant Cytol Histol 2009;31:233-238)