Anaplastic carcinoma arising from median ectopic thyroid (thyroglossal duct remnant).

The first case of anaplastic carcinoma arising in median ectopic thyroid (thyroglossal duct remnants) in an 84-year-old woman is presented. This expands the spectrum of histologic types of thyroid malignancies reported in this location and supports the theory that these carcinomas arise from thyroid rests associated with thyroglossal ducts. The presence of a histologically benign follicular neoplasm adjacent to the carcinoma suggests the possibility that the anaplastic carcinoma resulted from the transformation of an underlying well-differentiated tumor. Some unusual features of this case are discussed as well as the criteria for establishing the diagnosis of carcinoma arising in a thyroglossal duct remnant.