This midline neck lump is a thyroglossal cyst. The thyroid gland appears as an epithelial proliferation in the floor of the pharynx between the tuberculum impar and copula during the 4th week of development. From this site the thyroid gland descend anterior to the pharynx closely related to the hyoid bone. It reaches it's final position in front of the tracheal cartilages during the 7th week of development. During descent the gland remains connected to the base of the tongue by the thyroglossal duct that later disappears in most individuals.
Several aberrations can occur in the development of the thyroid gland.
A cystic remnant of the thyroglossal duct can persist causing a thyroglossal cyst. These can be found at any site in the path of descent of the thyroid gland but are usually found in close relationship to the hyoid bone. Rupture of thyroglossal cyst can result in a thyroglossal sinus. These are often erroneously termed thyroglossal fistulae. A thyroglossal fistula between the base of the tongue and neck skin due to persistence of the entire thyroglossal duct is very uncommon.