General
A variable number of small ovoid endocrine glands within the pretracheal fascia of the anterior neck, normally located on the posterior surface of the thyroid gland. Produces and secretes parathyroid hormone to maintain calcium and phosphate homeostasis.
Location
Typically four parathyroid glands (two pairs of superior and inferior glands located behind the left and right thyroid lobes):
- Superior parathyroid glands – located within the thyroid’s pretracheal fascial capsule, at the middle of the posterior border of each thyroid lobe, approximately 1cm superior to the entry of the inferior thyroid artery into the thyroid gland. Typically more constant in position.
- Inferior parathyroid glands – higher variability in location between individuals, however usually found near the inferior poles of the thyroid gland within 1-2 cm of the insertion of the inferior thyroid artery
Blood Supply
- Inferior thyroid artery – branch of thyrocervical trunk
- Predominant supply
- As it supplies the posterior aspect of the thyroid gland where the parathyroids are located
- Collateral arterial supply:
- Superior thyroid artery
- Thyroid ima artery
- Laryngeal artery
- Tracheal artery
- Oesophageal artery
Venous Drainage
- Superior, middle and inferior thyroid veins
- Superior and middle thyroid veins drain into the internal jugular vein
- Inferior thyroid vein drains into the brachiocephalic vein
Lymphatic Drainage
- Deep cervical lymph nodes
- Paratracheal lymph nodes
Innervation
Vasomotor supply by the:
- Middle cervical ganglion
- Inferior cervical ganglion
Relations
- Superior parathyroid glands
- Anteriorly: superior pole of the thyroid
- Inferiorly: Junction of the recurrent laryngeal and inferior thyroid artery
- Medially: oesophagus and trachea
- Laterally: common carotid artery
- Inferior parathyroid glands
- Anteriorly: inferior pole of the thyroid
- Posterior: plane of the recurrent laryngeal nerve
- Medially: oesophagus and trachea
- Laterally: common carotid artery
Embryological Development
- Superior parathyroid glands – derived from the fourth pharyngeal pouch
- Inferior parathyroid glands – derived from the third pharyngeal pouch with the thymus
- During embryological development, as the thymus migrates inferiorly, it displaces the inferior parathyroid glands caudally – hence the reversal of its position
Normal Variants
- Supernumerary glands (15%)
- Ectopic parathyroid gland – most commonly inferior to the inferior pole of the thyroid (e.g. thymus, retro-oesophageal region or superior mediastinum)
- Located within the thyroid gland
References