What causes a thyroglossal duct cyst?

• A. Failure of the duct to obliterate after thyroid migration from the foramen cecum
• B. Persistence of a second pouch
• C. Neural crest migration error
• D. Insufficient fusion of thyroid lobes

Answer: (A)

Thyroglossal duct cysts arise when the thyroglossal duct, the temporary tract linking the developing thyroid to the tongue, fails to disappear after the thyroid has migrated to its normal position in the neck. The thyroid begins at the foramen cecum on the base of the tongue and descends midline to its final location; normally the duct involutes, leaving no tract. If remnants persist, fluid-filled tissue can form a midline cyst along this path, often near the hyoid bone, and it may move with swallowing or tongue protrusion because of its attachment to the tongue and hyoid region. This explains the typical presentation and why removal often involves tracing and excising the duct from the tongue to the thyroid bed, sometimes with part of the hyoid (Sistrunk procedure) to prevent recurrence. The other options don’t fit because persistence of a second pouch would relate to branchial apparatus remnants, neural crest migration errors affect other craniofacial structures, and insufficient fusion of thyroid lobes is a different embryologic issue.