During reoperation for persistent primary hyperparathyroidism, an enlarged inferior parathyroid gland is found within the superior mediastinum embedded in thymic tissue. This ectopic position is explained by:

• A Migration along the thyroglossal tract into the chest
• B Failure of migration of the fourth pharyngeal pouch derivative
• C Aberrant development from the ultimobranchial body
• D Descent of the third pharyngeal pouch with the thymus during development ✓

Explanation

The inferior parathyroids arise from the dorsal aspect of the third pharyngeal pouch together with the thymus, and descend caudally with the thymic primordium. Because they travel further than the superior glands, their position is more variable, and thymic, intrathymic or mediastinal ectopia is common. Superior glands derive from the fourth pharyngeal pouch and remain relatively fixed near the cricothyroid junction, so option B describes the wrong pair of glands.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.