Parathyroid gland embryology

• Superior Parathyroid Gland – develops from the 4th Pharyngeal Pouch
• Inferior Parathyroid Gland – develops from the 3rd Pharyngeal Pouch
  • Displaced caudally by the descent of the Thymus from the same pouch
  • Thus, liable to end up in unusual positions

Third Pharyngeal Pouch

• Dorsal wing
  • Inferior parathyroid gland
    • Seventh week of gestation, the inferior parathyroid glands separate from the posterior pharyngeal wall and follow the path of the thymus, to reach their final destination on the posterior thyroid.
    • Due to the comparatively longer course, the final location of the inferior parathyroid is more variable, and ectopic parathyroid tissue can be found anywhere along their pathway of descent.
• Ventral wing
  • Formation of the thymus
    • Loses its connection with the pharyngeal wall and descends inferomedially to fuse with the contralateral portion in the anterior mediastinum.

Fourth Pharyngeal Pouch

• Dorsal wing
  • Superior parathyroid gland
    • Seventh week of development, the parathyroid glands separate from the pharyngeal wall and attach to the posterior surface of the thyroid.
• Ventral wing
  • Ultimobranchial body
    • Fuses with the posterolateral thyroid and give rise to the parafollicular C-cells of the thyroid.