The Parathyroid Glands
The parathyroid glands are small endocrine glands located in the anterior neck. They are responsible for the production of parathyroid hormone, which acts to control calcium levels in the body.
This article will consider the anatomical location, vessels and nerves of the parathyroid glands, as well as some clinical correlations.
The parathyroid glands are located on the posterior aspect of the lateral lobes of the thyroid gland. They are flattened and oval in shape, situated external to the gland itself, but within its sheath.
The majority of people have four parathyroid glands, although variation in number is common. Anatomically, the glands can be divided into two pairs:
- Superior parathyroid glands – Derived embryologically from the fourth pharyngeal pouch. They are located approximately 1cm superior to the entry of the inferior thyroid arteries into the thyroid gland (at level of the inferior border of the cricoid cartilage).
- Inferior parathyroid glands – Derived embryologically 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 percentage of people, the glands can be found as far inferiorly as the superior mediastinum.
The posterior aspect of the thyroid gland is supplied by the inferior thyroid arteries. Thus its branches also supply the nearby parathyroid glands. Collateral circulation is delivered by the superior thyroid arteries, thyroid ima artery, and laryngeal, tracheal and oesophageal arteries.
The parathyroid veins drain into the thyroid plexus of veins.
The lymphatic vessels of the parathyroid glands drain (along with those of the thyroid gland) into the deep cervical lymph nodes and paratracheal lymph nodes.
The parathyroid glands have an extensive supply of nerves, derived from thyroid branches of the cervical (sympathetic) ganglia.
It is important to note that these nerves are vasomotor, not secretomotor – endocrine secretion of parathyroid hormone is controlled hormonally.
Clinical Relevance: Surgical Damage to Parathyroid Glands
The inconsistency in location of the parathyroid glands between individuals increases their risk of being damaged or removed inadvertently during neck surgery (i.e. thyroidectomy).
Removal of all the parathyroid glands would cause decreased serum calcium levels (hypocalcaemia), in turn leading to tetany (severe muscle twitches and cramps). Without urgent treatment this will result in death.
In order to try and prevent parathyroid damage, surgeons may preserve the posterior part of the thyroid gland during thyroidectomy. If this is not possible, the parathyroid glands are carefully located prior to removal of the thyroid tissue.