Thyroid dysgenesis thyroid gland may be located anywhere along the path of the descent of the thyroid during its embryological development, although it is most commonly located at the base of the tongue, just posterior to the foramen cecum of the tongue. In this location, an aberrant or ectopic thyroid gland is known as a "lingual thyroid". If the thyroid fails to descend to even higher degree, then the resulting final resting point of the thyroid gland may be high in the neck, such as just below the hyoid bone. Parts of ectopic thyroid tissue ("accessory thyroid tissue") can also occur, and
Computed tomography of the thyroid of normally sited thyroid gland in US and CT scans also supports the diagnosis. In addition, US can guide FNA for cytological confirmation of a thyroid lesion. Ectopic thyroid tissue appears as a well-circumscribed, homogeneous, highly attenuating mass relative to adjacent muscles. Normally, it enhances avidly following the administration of iodinated contrast. Ectopic thyroid tissue may be detected in the tongue near the foramen cecum (90 %) and along the midline between the thyroid isthmus and posterior tongue, lateral neck, mediastinum, and oral cavity. The most frequent location is the base of the tongue (Figs. 16, ,1717 and and18).18). In