The thyroglossal duct is an epithelium-lined connection between the foramen cecum and the thyroid that forms during the descent of the thyroid during embryological development. It usually involutes in the 8th-10th week of gestation.
The thyroglossal duct arises from proximal primitive foregut between the first and second pharyngeal pouches at the foramen cecum, located at the junction of the anterior two thirds and posterior third of the tongue . From there it passes anterior to the body of the hyoid bone, curving backwards and superiorly to reach behind the bone before once more turning inferiorly and continuing to the isthmus of the thyroid. The pyramidal lobe, if present, marks this point. The tip of the duct bifurcates, forming the two lobes of the gland. The parafollicular cells (C cells) responsible for calcitonin production are derived from separate tissue, the ultimobranchial body, a small diverticulum of the fourth pharyngeal pouch.
The thyroid may halt at any stage during its descent or leave rests of thyroid tissue along the course of the thyroglossal duct :
Failure of obliteration of the duct may lead to the formation of a thyroglossal duct cyst.