A 12-year-old girl presents to the clinic for evaluation of a painless neck mass that has slowly enlarged over several months. Past medical history is negative. Physical examination shows a 2-cm, smooth, mobile mass in the midline just inferior to the hyoid bone. The mass elevates when the patient swallows and when she protrudes her tongue. There is no cervical lymphadenopathy.
Persistence of which of the following embryologic structures most directly accounts for this lesion?
The correct answer is:
D) Thyroglossal duct
The thyroid gland begins at the foramen cecum on the dorsal surface of the developing tongue and descends through the neck along the thyroglossal duct. The duct normally involutes after the thyroid reaches its final position anterior to the upper trachea. Persistence of any portion of the thyroglossal duct can produce a thyroglossal duct cyst. These cysts are usually located in the midline near or below the hyoid bone. They move with swallowing and tongue protrusion because the tract remains connected to structures at the tongue base and is closely associated with the hyoid bone.
Answer choice A: Cervical sinus, is incorrect. Persistence of the cervical sinus can produce a lateral cervical cyst or branchial cleft cyst, typically located along the anterior border of the sternocleidomastoid muscle. It does not usually move with tongue protrusion.
Answer choice B: First pharyngeal cleft, is incorrect. The first pharyngeal cleft forms the external auditory canal. Developmental abnormalities may produce preauricular or periauricular cysts and fistulas rather than a midline neck mass.
Answer choice C: Second pharyngeal pouch, is incorrect. The second pharyngeal pouch contributes to formation of the palatine tonsillar epithelium. It is not the origin of a midline cyst that moves with swallowing.
Answer choice E: Ultimobranchial body, is incorrect. The ultimobranchial body gives rise to the parafollicular C cells of the thyroid gland. Its persistence does not produce a thyroglossal duct cyst.
Key Learning Point
A thyroglossal duct cyst is a midline neck mass near the hyoid bone that moves with swallowing and tongue protrusion due to persistence of the embryologic thyroglossal duct.
