The inferior thyroid artery is a major branch of the thyrocervical trunk, which arises from the first part of the subclavian artery. This artery is primarily responsible for supplying blood to the thyroid gland, as well as surrounding structures in the neck.
Location
The inferior thyroid artery originates from the thyrocervical trunk, a branch of the subclavian artery. From its origin, it ascends in the neck, traveling behind the common carotid artery and the internal jugular vein. It courses medially toward the lower part of the thyroid gland, where it provides its vascular supply. The artery also sends branches to the parathyroid glands, the esophagus, and parts of the trachea. It typically enters the lower pole of the thyroid gland and forms anastomoses with the superior thyroid artery, ensuring adequate blood flow to the gland.
Structure and Anatomy
Origin
The inferior thyroid artery arises from the thyrocervical trunk, which itself is a branch of the subclavian artery. The thyrocervical trunk also gives rise to other important arteries, including the transverse cervical artery, suprascapular artery, and ascending cervical artery. The inferior thyroid artery is the largest branch of the thyrocervical trunk and is essential in providing blood supply to the thyroid and other structures in the neck.
Course
After originating from the thyrocervical trunk, the inferior thyroid artery ascends medially toward the thyroid gland. It travels posterior to the common carotid artery and the internal jugular vein, and as it moves upward, it approaches the lower part of the thyroid gland. The artery typically passes in front of the vertebral artery and runs parallel to the trachea and esophagus on its way to the thyroid.
Relations
- Anteriorly: The artery is related to the common carotid artery and internal jugular vein as it courses upward in the neck.
- Posteriorly: The artery lies anterior to the vertebral artery and the anterior scalene muscle.
- Laterally: The phrenic nerve often runs close to the inferior thyroid artery, on its way to the diaphragm, making this relationship important during surgical procedures.
- Medially: The artery is closely related to the lower pole of the thyroid gland, as well as to the parathyroid glands, trachea, and esophagus.
Branches
The inferior thyroid artery gives off several smaller branches as it courses toward its final destination:
- Esophageal branches: These small arteries provide blood to the esophagus in the cervical region.
- Tracheal branches: These branches supply the trachea with blood, ensuring proper vascularization for the upper portion of the respiratory tract.
- Pharyngeal branches: In some cases, the artery sends small branches to the pharynx, contributing to the blood supply of the upper respiratory and digestive pathways.
- Parathyroid branches: The inferior thyroid artery also supplies the parathyroid glands, which are located on the posterior surface of the thyroid gland.
Terminal Branches and Thyroid Gland Supply
As the artery approaches the lower part of the thyroid gland, it divides into multiple smaller branches that enter the lower pole of the thyroid. These branches ensure the vascular supply to the gland, forming anastomoses with branches of the superior thyroid artery, which originates from the external carotid artery. The anastomoses between the superior and inferior thyroid arteries provide a consistent and rich blood supply to the thyroid, ensuring proper gland function.
Anastomoses
The inferior thyroid artery forms several important anastomoses with other arteries in the neck:
- Superior thyroid artery: This artery, a branch of the external carotid artery, forms anastomoses with the inferior thyroid artery at the thyroid gland, ensuring continuous blood flow to the gland even if one of the arteries is compromised.
- Ascending cervical artery: In some cases, the inferior thyroid artery forms anastomoses with small branches of the ascending cervical artery, which also arises from the thyrocervical trunk.
- Tracheal and esophageal arteries: The inferior thyroid artery may also connect with other small arteries supplying the trachea and esophagus, helping to maintain vascularization to these vital structures.
Variations
There is some anatomical variability in the course and origin of the inferior thyroid artery. In rare cases, the artery may arise directly from the subclavian artery rather than the thyrocervical trunk. Additionally, the size and branching pattern of the artery can vary between individuals, particularly in terms of how many branches it gives off to the thyroid gland and other nearby structures.
Termination
The inferior thyroid artery terminates by dividing into its terminal branches that penetrate the lower pole of the thyroid gland. These branches supply the gland’s inferior portion and posterior surface, ensuring adequate blood flow to the lower part of the thyroid. It also supplies the parathyroid glands before completing its course.
Function
The inferior thyroid artery plays a critical role in supplying blood to key structures in the neck, particularly the thyroid gland, parathyroid glands, and surrounding tissues. Its function ensures that these vital organs receive sufficient oxygenated blood to support their metabolic and endocrine activities, as well as maintaining proper function in nearby structures such as the trachea, esophagus, and pharynx.
Blood Supply to the Thyroid Gland
The primary function of the inferior thyroid artery is to provide oxygenated blood to the thyroid gland, which is responsible for regulating metabolism, growth, and other essential bodily functions through the secretion of thyroid hormones. The artery approaches the lower pole of the thyroid gland, where it divides into multiple small branches that penetrate the gland, particularly supplying the inferior and posterior portions of the gland.
The artery also forms anastomoses with the superior thyroid artery, which originates from the external carotid artery. This anastomotic network ensures that blood flow to the thyroid gland remains continuous and robust, even if one of the arteries becomes compromised. This redundancy is essential for the gland’s function, as it relies on a rich blood supply to sustain its high metabolic activity.
Blood Supply to the Parathyroid Glands
Another important function of the inferior thyroid artery is to supply blood to the parathyroid glands, small endocrine glands located on the posterior surface of the thyroid. These glands regulate calcium levels in the blood through the secretion of parathyroid hormone (PTH). The parathyroid glands are often closely associated with the branches of the inferior thyroid artery, which ensures that they receive the oxygen and nutrients necessary for maintaining calcium balance in the body.
Without sufficient blood supply from the inferior thyroid artery, the parathyroid glands may experience ischemia or functional impairment, which could lead to calcium imbalances and related health issues.
Blood Supply to the Trachea and Esophagus
The inferior thyroid artery also supplies several small branches to the trachea and esophagus in the cervical region. These branches are responsible for vascularizing the upper part of the trachea and esophagus, supporting the structural integrity of these vital respiratory and digestive organs. The tracheal branches ensure that the trachea, which forms part of the airway, has adequate blood flow for maintaining its epithelial lining and cartilage structure.
Similarly, the esophageal branches of the inferior thyroid artery provide vascular support to the upper esophagus, ensuring proper blood flow to the mucosal and muscular layers that allow for normal swallowing and movement of food.
Blood Supply to the Pharynx and Larynx
In some cases, the inferior thyroid artery sends small branches to the pharynx and larynx, contributing to the vascularization of the upper respiratory and digestive tracts. The artery’s pharyngeal branches help supply the muscles and mucosa of the pharynx, which plays a role in swallowing and protecting the airway during respiration. The laryngeal branches may also assist in supplying the larynx, particularly the lower part of the voice box, ensuring adequate blood flow to the vocal cords and surrounding tissues that support speech and breathing.
Formation of Anastomoses for Collateral Circulation
The inferior thyroid artery forms important anastomoses with the superior thyroid artery, which originates from the external carotid artery, and occasionally with other arteries like the ascending cervical artery. These anastomoses are critical for ensuring that blood flow to the thyroid and surrounding structures remains uninterrupted in case of occlusion or damage to one of the main arteries. This collateral circulation supports the gland’s function even in the presence of arterial blockages or during thyroid surgeries, reducing the risk of ischemic damage to the thyroid and adjacent tissues.
Support for Tissue Regeneration and Healing
By providing a rich blood supply to the thyroid gland, parathyroid glands, trachea, esophagus, and surrounding tissues, the inferior thyroid artery supports tissue regeneration and healing. This function is essential for maintaining the health of the neck structures, especially following injury, surgery, or inflammation. Adequate blood flow ensures that tissues receive the oxygen and nutrients they need for repair, while removing metabolic waste products that can accumulate after damage.
In surgical contexts, such as thyroidectomy (removal of the thyroid gland), it is important to preserve the branches of the inferior thyroid artery to avoid compromising blood supply to the remaining parts of the gland and the parathyroid glands. Proper blood supply is critical for minimizing postoperative complications and promoting effective healing.
Nutrient Supply to Cervical and Thyroid Tissues
The inferior thyroid artery ensures that the thyroid gland, parathyroid glands, and surrounding tissues receive an adequate supply of oxygen, glucose, and other nutrients necessary for their metabolic functions. The thyroid gland, in particular, has a high metabolic rate due to its role in hormone production, making a reliable and abundant blood supply essential for maintaining normal thyroid function.
Clinical Significance
The inferior thyroid artery is clinically significant due to its essential role in supplying blood to the thyroid gland, parathyroid glands, and nearby structures such as the trachea and esophagus. In surgical procedures involving the thyroid, such as thyroidectomy (removal of the thyroid gland), special care must be taken to avoid damaging the inferior thyroid artery and its branches. Accidental injury to the artery can lead to excessive bleeding or compromise blood flow to the parathyroid glands, potentially causing hypocalcemia (low blood calcium levels) due to impaired parathyroid function.
The artery’s close relationship with the recurrent laryngeal nerve, which runs alongside it, adds another layer of clinical importance. Injury to the recurrent laryngeal nerve during thyroid surgery can result in vocal cord paralysis and voice changes, highlighting the need for precise surgical technique in this area.
In cases of thyroid enlargement (goiter) or thyroid tumors, the inferior thyroid artery may become more prominent or prone to complications. Its role in forming anastomoses with other arteries, like the superior thyroid artery, also makes it important in maintaining collateral circulation in the neck region during vascular blockages or trauma.
