A surgeon performing total thyroidectomy finds a parathyroid gland lying within the thymic tongue in the superior mediastinum. Embryologically, this ectopic gland most likely arose from which pharyngeal pouch?

• A First pharyngeal pouch
• B Second pharyngeal pouch
• C Third pharyngeal pouch ✓
• D Fourth pharyngeal pouch

Explanation

The inferior parathyroids develop from the third pharyngeal pouch together with the thymus. Because they migrate caudally with the thymus for a longer distance than the fourth pouch derivatives, they can be pulled down into the lower neck or superior mediastinum, explaining their greater positional variability. The superior parathyroids from the fourth pouch remain close to the cricothyroid junction and are far more constant in position. This paradoxical descent is a classic embryology examination point.

Reference: Langman's Medical Embryology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.