Parathyroid Anatomy

The Anatomy of the Parathyroid Glands

The parathyroid glands are endocrine glands located in the anterior neck, responsible for the production of parathyroid hormone (PTH), which acts to increase the level of serum calcium. In this article, we shall look at the anatomy of the parathyroid glands – their location, neurovascular supply, and clinical correlations.

Anatomical Location

The parathyroid glands are usually located on the posterior aspect of the thyroid gland, flattened and oval in shape, situated external to the thyroid gland itself but within the pretracheal fascia. Most individuals have four parathyroid glands, although variation in number (from two to six) is common.

• Superior parathyroid glands (x2) – derived from the fourth pharyngeal pouch. They are located 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.
• Inferior parathyroid glands (x2) – derived from the third pharyngeal pouch. Although inconsistent in location between individuals, the inferior parathyroid glands are usually found near the inferior poles of the thyroid gland. In a small number of people, the inferior parathyroid glands can be found as far inferiorly as the superior mediastinum.

Vasculature

The vascular supply is similar to that of the thyroid gland. Arterial supply is chiefly via the inferior thyroid artery (as this artery supplies the posterior aspect of the thyroid gland - where the parathyroids are located). Collateral arterial supply is from the superior thyroid artery and thyroid ima artery. Venous drainage is into the superior, middle, and inferior thyroid veins.

Lymphatics

The lymphatic drainage from the parathyroid glands is to the paratracheal and deep cervical nodes.

Nerves

The parathyroid glands have an extensive supply of sympathetic nerves derived from thyroid branches of the cervical ganglia. It is important to note that these nerves are vasomotor – not secretomotor. This means that endocrine secretion of parathyroid hormone is under hormonal control.

Clinical Relevance - Parathyroid Glands and Hypocalcaemia

Due to their location on the posterior aspect of thyroid gland, the parathyroid glands are at a high risk of being damaged or removed inadvertently during thyroid surgery. This can result in an acute drop in serum calcium, a condition known as hypocalcaemia. Clinical features of hypocalcaemia include signs of tetany, such as muscle cramps and paraesthesia of the fingers, toes, and mouth.

Because of the risk of hypocalcaemia, it is usually standard post-operative practice to check the parathyroid hormone and serum calcium in all patients following thyroid surgery. This helps to ensure that no damage has been done to the parathyroid glands during the procedure, preventing any issues with calcium metabolism resulting from hypocalcaemia.