Papillary adenocarcinoma of the thyroid in a thyroglossal duct cyst.

A case report is presented of an 8-year-old boy who underwent resection of a thyroglossal duct cyst to illustrate a rare, but significant, complication of a common clinical problem. Pathological examination revealed that it contained a papillary adenocarcinoma of the thyroid, presumably arising from ectopic glandular tissue in the cyst. Thyroglossal duct cysts are a common cause of midline neck masses in children. Occult thyroid carcinoma is a rare co-morbid finding. It infrequently leads to death, but thyroglossal duct cysts may also contain the only functioning, albeit ectopic, thyroid tissue. Patients with clinical thyroglossal duct cysts should be carefully evaluated preoperatively for the presence of tumor and other functioning thyroid tissue prior to excision of the cyst.