Thryroglossal Duct

The thyroid gland develops as an endodermal outpocketing from the floor of the pharynx in the region of the foramen cecum. The significance of this foramen is that it indicates the point at which the anterior 2/3 of the tongue (1st pharyngeal arch derivative) is joined by the posterior 1/3 of the tongue (3rd pharyngeal arch derivative). The thyroid gland migrates inferiorly from this position anterior to the hyoid bone and larynx to come to lie anterior to the upper tracheal rings. The migration of the thyroid is guided by a duct that retains the connection of the thyroid gland to the foramen cecum of the tongue. This duct is called the thyroglossal duct.

This duct usually disappears after the thyroid gland reaches its final destination. Sometimes, this duct persists as is shown in this dissection finding. The thyroglossal duct can develop into a pyramidal lobe of the thyroid gland. Remnants of this duct can perist as midline cysts called thyroglossal duct cysts. These can be located anywhere along the migratory path of the thyroid gland but generally have a midline location. Palpation of the cysts as they move up and down during swallowing is one clinical sign of the existence of thyroglossal duct cysts.

Figure 1

The thyroglossal duct (indicated by the arrow) is pictured above in the midline neck of a male cadaver. The duct connects the thyroid gland with the foramen cecum of the tongue and is indicative of the close embryological relationship of the thyroid to the tongue. In this photograph, the head (indicated by the mandible) is superior and the chest inferior.

Figure 2

This is a close-up view of the neck region of the same cadaver. The thyroglossal duct (5) can be seen inferior to the hyoid bone (6) and anterior to the thyroid cartilage (3). The duct connects the thyroid gland (4) inferiorly with the foramen cecum of the tongue (not shown) superiorly. The internal jugular vein (1) and common carotid artery (2) are seen laterally to the thyroid gland.