A 2-year-old boy is found to have an ectopic thyroid gland at the base of the tongue (lingual thyroid). This represents failure of descent of the thyroid along which embryological path?

• A From the first pharyngeal pouch, descending along the thyrohyoid membrane
• B From the third pharyngeal pouch, migrating inferiorly alongside the parathyroid glands
• C From the foramen cecum of the tongue, descending through the thyroglossal duct anterior to the hyoid and thyroid cartilages ✓
• D From the ultimobranchial body of the fourth pharyngeal pouch

Explanation

The thyroid gland develops from an endodermal diverticulum at the foramen cecum — the junction of the anterior two-thirds and posterior one-third of the tongue — during the fourth week. It descends in the midline through the thyroglossal duct, passing anterior to the hyoid bone and thyroid cartilage, to reach its final pretracheal position by week 7. Failure of descent at any point along this path leaves thyroid tissue at an ectopic site; arrest at the tongue base produces a lingual thyroid, which may be the only functioning thyroid tissue in the body.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.