Abnormal migration of the median thyroid anlage may take the form of either nondescent or maldescent. Nondescent of the thyroid produces the clinical syndrome of lingual thyroid, in which the entire tissue is located at the base of the tongue3,4,5 and 6 (see Chap. 47). Maldescent may cause thyroid tissue to remain along the pathway of the thyroglossal duct or in the trachea, larynx, or posterior pharynx.4,5 Elongated descent into the superior mediastinum may lead to substernal, preaortic, or pericardial thyroid.3,7