thyroglossal duct cyst

During development, the thyroid gland originates from the foramen cecum at the base of the tongue and descends through the neck via the thyroglossal duct to reach its final position anterior to the trachea. Normally, this duct involutes completely. Failure of involution leaves a persistent epithelial-lined tract that can form a cystic structure anywhere along this path of descent, most commonly near or just below the hyoid bone.

Clinically, thyroglossal duct cysts present as painless, midline (or near-midline) neck masses that characteristically elevate with swallowing and tongue protrusion due to their attachment to the foramen cecum via the duct. They typically present in children or young adults, though can present later in life. Infection (leading to sudden painful enlargement) is a common complication, and rarely, papillary thyroid carcinoma can arise within the cyst (a key testable association).

Diagnosis is often clinical, supported by ultrasound to confirm cystic nature and, importantly, to confirm the presence of a normal orthotopic thyroid gland (since ectopic thyroid tissue may be the only functioning thyroid tissue in some patients, and removing it without recognizing this could cause hypothyroidism).

Treatment is the Sistrunk procedure, which involves surgical excision of the cyst along with the central portion of the hyoid bone and a core of tissue up to the base of the tongue, to reduce recurrence risk (recurrence rates are much higher with simple cyst excision alone since remnant epithelial tracts near the hyoid bone can persist).

Key differentiating point for boards: differentiate from a branchial cleft cyst, which is typically lateral in the neck (usually second branchial cleft origin) and does NOT move with swallowing.