During neck exploration for primary hyperparathyroidism, an enlarged gland is found within the thymic tongue in the lower anterior mediastinum. This ectopic parathyroid results from abnormal descent with which embryological structure?

• A Third pharyngeal pouch derivatives migrating caudally ✓
• B Fourth pharyngeal pouch derivatives migrating caudally
• C Ultimobranchial body of the fifth pharyngeal pouch
• D Thyroglossal duct remnant extending into the mediastinum

Explanation

The inferior parathyroids arise from the third pharyngeal pouch together with the thymus. Because they descend further than the fourth pouch structures, they can be dragged into an ectopic position along the thymopharyngeal tract, commonly within or near the thymus in the anterior mediastinum. Superior parathyroids from the fourth pouch have a shorter descent and rarely become mediastinal, which is why mediastinal adenomas are almost always inferior glands.

Reference: Gray's Anatomy for Students, 4th ed.

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Written and medically reviewed by the StethoPrep medical team.