Learning objective
Understand the anatomy, blood supply, and clinical significance of the parathyroid glands, and recognize their role in calcium homeostasis.
The parathyroid glands are small endocrine glands located in the anterior neck. They secrete parathyroid hormone (PTH), which increases serum calcium by acting on bone, kidney, and the gut.
In this article, we will explore their anatomical location, vascular and neural supply, and clinical relevance.
Anatomical location
The parathyroid glands are typically situated on the posterior aspect of the thyroid gland, external to the thyroid itself but within the pretracheal fascia. They are flattened and oval in shape.
- Most individuals have four parathyroid glands, but the number can vary from two to six.
- Superior parathyroid glands (x2) – derived from the fourth pharyngeal pouch, usually located at the middle of the posterior border of each thyroid lobe, ~1 cm above the entry of the inferior thyroid artery.
- Inferior parathyroid glands (x2) – derived from the third pharyngeal pouch, often found near the inferior poles of the thyroid, but may occasionally descend into the superior mediastinum.
Vasculature
- Arterial supply: primarily from the inferior thyroid artery; collateral supply from the superior thyroid artery and occasionally the thyroid ima artery.
- Venous drainage: into the superior, middle, and inferior thyroid veins.
- Lymphatic drainage: to paratracheal and deep cervical nodes.
Nerves
The parathyroid glands receive sympathetic innervation from thyroid branches of the cervical ganglia. These nerves are vasomotor only; hormonal secretion of PTH is controlled by serum calcium levels, not nerves.
Clinical relevance
Post-thyroidectomy hypocalcaemia:
Because of their close relationship with the thyroid, the parathyroid glands are at risk of inadvertent removal or damage during thyroid surgery.
- Result: acute hypocalcaemia
- Symptoms: tetany, muscle cramps, paraesthesia of the fingers, toes, and mouth
- Management: post-operative monitoring of serum calcium and PTH levels
