Embryology, Anatomy, and Histology of the Parathyroid Glands

Embryology

• Parathyroid glands are of endodermal origin and originate as symmetric, nodular epithelial proliferations on the dorsal aspects of the third and fourth pharyngeal pouches around the fifth week of gestation.

• Superior gland develops from the fourth pharyngeal pouch, which is connected with the pharynx, from which it separates. The fourth pharyngeal pouch is a complex bilobed structure composed of a ventral component; the ultimobranchial body, which fuses with the lateral aspect of the thyroid lobe; and a dorsal epithelial proliferation, which separates to become the superior thyroid gland, assuming the usual adult position along the posteromedial aspect of the thyroid gland. The superior parathyroid glands tend to be more constant in position than the inferior glands.

• Inferior parathyroid glands develop from the third pharyngeal pouch, also a complex bilobed structure, associated with the thymus, from which it separates after migrating caudally to a position near the lower pole of the thyroid gland.

• Most common “anomaly” of the parathyroid glands is ectopia, which usually represents a variation in embryologic migratory pattern.

• Parathyroid agenesis is very rare:

  • DiGeorge syndrome includes:

    • –

      Complete or partial absence of the third and fourth pharyngeal pouches and their derivatives: the thymus, the parathyroid glands, and the C cells

    • –

      Disease is manifested by multiple facial malformations, hypoplasia of the thyroid, hypoparathyroidism, and cardiac abnormalities.