Thyroglossal Duct Cyst

Epidemiology

Thyroglossal duct cyst is a congenital lesion that arises from anomalous development and migration of the thyroid gland. Thyroglossal duct cyst is the most common midline neck mass in children. The majority of cases present in children < 10 years of age. These lesions may be seen in young adults. Less than 2% of cases arise in patients > 60 years of age. No gender predilection has been reported.

Clinical Findings

Thyroglossal duct cysts usually present as nontender, gradually increasing midline neck masses. The average size at presentation is 2 to 4 cm. Recent enlargement may occur as a result of an associated upper respiratory tract infection. Because thyroglossal duct cysts are often attached to the tongue or hyoid bone, these lesions characteristically move when the tongue is protruded. Thyroglossal duct cyst may arise anywhere along the course of migration of the embryonic thyroglossal duct and thyroid gland. The most common location is below the level of the hyoid bone (65%). Twenty percent of thyroglossal duct cysts are suprahyoid in location, whereas 15% of lesions are located at the level of the hyoid bone. Seventy-five percent of thyroglossal duct cysts are midline or slightly off the midline.

Embryology

The thyroid gland is the first endocrine gland to appear in the developing fetus and begins its embryogenesis around the 24th day of gestation. The gland arises from an endodermal thickening in the midline of the developing tongue base. This area is known as the foramen cecum and is located posterior to the apex of the circumvallate papilla. The thyroid gland descends as a result of elongation of the embryo and growth of the tongue. The developing gland migrates as a bilobed diverticulum and forms an epithelial lined cord during descent. Normal involution of the thyroglossal duct occurs between the eighth and tenth weeks of gestation. Failure of involution of the epithelial cord predisposes the patient to formation of a thyroglossal duct cyst. Cyst formation is believed to be due to either inflammatory changes that stimulate secretion of fluids within the ductal remnants or trapping of fluids produced from residual secretory epithelium located in the epithelial cord remnant.

During descent, the developing cartilage of the second branchial arch that gives rise to the hyoid bone comes in close proximity to the descending thyroglossal duct. The thyroid gland may descend superficial to, through, or deep to the hyoid bone. As a result, the location of thyroglossal duct cysts with the hyoid bone is variable. The duct then continues its downward course and lies anterior to the thyrohyoid membrane. The duct terminates at the superior border of the thyroid gland. Migration of the thyroid gland is completed by the eighth week of gestation.