The superior thyroid artery is one of the first branches of the external carotid artery, playing a key role in supplying blood to the thyroid gland and surrounding structures in the neck. It is a small but significant artery within the vascular network of the neck.
Location
The superior thyroid artery originates from the external carotid artery near its bifurcation from the common carotid artery, typically just above the level of the superior border of the thyroid cartilage (around the level of the fourth cervical vertebra). From its origin, the artery descends anteriorly toward the thyroid gland, running alongside the larynx. It gives off several smaller branches that supply adjacent muscles, the larynx, and eventually the thyroid gland, which is its primary target. The artery also forms anastomoses with branches from the inferior thyroid artery to ensure a rich blood supply to the gland.
Structure and Anatomy
Origin
The superior thyroid artery arises from the external carotid artery, typically near the external carotid’s origin from the common carotid artery. It is usually the first branch of the external carotid artery, located just above the bifurcation of the common carotid artery at the level of the superior border of the thyroid cartilage, near the fourth cervical vertebra (C4).
Course
After originating from the external carotid artery, the superior thyroid artery descends anteriorly and medially toward the thyroid gland. As it travels, it runs alongside the larynx, following the contour of the thyroid cartilage. The artery then moves downward, entering the upper part of the thyroid gland, primarily on its anterolateral surface.
Branches
The superior thyroid artery gives off several important branches that supply surrounding structures in addition to the thyroid gland itself:
- Infrahyoid Branch: This small branch supplies the infrahyoid muscles located at the front of the neck. These muscles include the sternohyoid, sternothyroid, omohyoid, and thyrohyoid muscles, all of which play a role in swallowing and neck movement.
- Sternocleidomastoid Branch: This branch supplies the sternocleidomastoid muscle, a key muscle involved in head rotation and neck flexion. The branch often arises separately or as part of the common trunk with the infrahyoid branch.
- Superior Laryngeal Artery: A significant branch of the superior thyroid artery, the superior laryngeal artery travels medially and pierces the thyrohyoid membrane to supply the larynx. It provides blood to the mucous membranes and intrinsic muscles of the larynx, contributing to vocal cord function. This artery often accompanies the internal branch of the superior laryngeal nerve, which is important for innervating the larynx.
- Cricothyroid Branch: This small branch supplies the cricothyroid muscle, which plays a role in the tension and elongation of the vocal cords. The cricothyroid muscle is important for modulating voice pitch.
Termination
The superior thyroid artery terminates by dividing into anterior and posterior branches, which distribute blood to the upper portion of the thyroid gland. These terminal branches supply the glandular tissue of the thyroid, ensuring adequate blood flow for hormone production and overall thyroid function. The artery also forms anastomoses with the inferior thyroid artery, which arises from the thyrocervical trunk (a branch of the subclavian artery), providing a rich blood supply to the entire thyroid gland.
Relationship to Nearby Structures
As it descends toward the thyroid gland, the superior thyroid artery is closely related to several important anatomical structures in the neck:
- Larynx: The artery runs alongside the larynx, with one of its branches, the superior laryngeal artery, supplying the mucous membranes and intrinsic muscles of the larynx.
- Thyroid Cartilage: The superior thyroid artery runs near the superior border of the thyroid cartilage, following the contour of this structure as it moves downward toward the thyroid gland.
- Thyrohyoid Membrane: The superior laryngeal artery, a branch of the superior thyroid artery, pierces the thyrohyoid membrane to enter the larynx.
- Sternocleidomastoid Muscle: The artery supplies the sternocleidomastoid muscle through its muscular branches.
Anastomoses
The superior thyroid artery forms anastomoses with the inferior thyroid artery, which arises from the thyrocervical trunk (a branch of the subclavian artery). This network of anastomoses ensures a continuous and reliable blood supply to the thyroid gland, even if one of the arteries is compromised.
In addition to anastomosing with the inferior thyroid artery, the superior thyroid artery forms connections with nearby vessels, including the cricothyroid branch of the superior laryngeal artery. These anastomoses contribute to the rich vascular network in the neck region, ensuring the health of the thyroid gland, larynx, and surrounding tissues.
Variations
The anatomy of the superior thyroid artery can show individual variations. In some cases, the artery may originate directly from the common carotid artery, rather than the external carotid artery. Additionally, the branching patterns of the superior thyroid artery can vary, particularly in its supply to nearby muscles and the larynx. Variations in the origin, course, or branching pattern are important considerations during surgical procedures in the neck, such as thyroidectomy or laryngeal surgeries.
Surrounding Vascular Structures
The superior thyroid artery is located near several other key vascular structures in the neck:
- Common Carotid Artery: The superior thyroid artery arises near the bifurcation of the common carotid artery, from which it receives its blood supply.
- External Jugular Vein: As the superior thyroid artery descends toward the thyroid gland, it runs near the external jugular vein, which drains deoxygenated blood from the head and neck.
- Inferior Thyroid Artery: The superior thyroid artery forms anastomoses with the inferior thyroid artery, which arises from the thyrocervical trunk and supplies the lower part of the thyroid gland.
Relationship with Nerves
The superior thyroid artery is closely associated with several important nerves:
- Internal Branch of the Superior Laryngeal Nerve: This nerve accompanies the superior laryngeal artery as it enters the larynx by piercing the thyrohyoid membrane. It provides sensory innervation to the mucous membrane of the larynx above the vocal cords.
- External Branch of the Superior Laryngeal Nerve: This branch of the superior laryngeal nerve runs close to the superior thyroid artery and innervates the cricothyroid muscle, contributing to vocal cord tension and voice modulation.
Function
Blood Supply to the Thyroid Gland
The primary function of the superior thyroid artery is to supply oxygenated blood to the thyroid gland, which is critical for the gland’s metabolic and endocrine functions. The artery provides blood to the upper portion of the thyroid gland, ensuring that the gland receives the nutrients and oxygen it needs to produce thyroid hormones such as thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolism, growth, and energy production in the body. By maintaining a steady blood flow to the thyroid gland, the superior thyroid artery supports its vital role in endocrine function.
Blood Supply to the Larynx
Through the superior laryngeal artery, a significant branch of the superior thyroid artery, it provides blood to the larynx. The larynx, or voice box, plays a critical role in phonation, respiration, and airway protection. The superior laryngeal artery passes through the thyrohyoid membrane to supply blood to the mucous membranes and intrinsic muscles of the larynx, including the vocal cords. By ensuring a continuous blood flow to the larynx, the superior thyroid artery supports voice production and the proper functioning of the airway.
Blood Supply to the Infrahyoid Muscles
The superior thyroid artery gives off the infrahyoid branch, which supplies the infrahyoid muscles. These muscles, including the sternohyoid, sternothyroid, omohyoid, and thyrohyoid, play a role in swallowing, speech, and movement of the hyoid bone and larynx. By delivering blood to these muscles, the superior thyroid artery supports their function, allowing for the coordinated movement of the neck and throat during activities like swallowing and vocalization.
Blood Supply to the Sternocleidomastoid Muscle
The sternocleidomastoid branch of the superior thyroid artery supplies the sternocleidomastoid muscle, a large muscle that is essential for head and neck movement. The sternocleidomastoid muscle enables movements such as head rotation, neck flexion, and lateral bending. The superior thyroid artery ensures that the muscle receives adequate oxygen and nutrients for proper functioning, especially during activities that require head movement and stability.
Contribution to Vocal Cord Function
Through the cricothyroid branch, the superior thyroid artery supplies the cricothyroid muscle, which plays a crucial role in adjusting the tension of the vocal cords. The cricothyroid muscle elongates and tightens the vocal cords, modulating pitch during speech or singing. By delivering blood to the cricothyroid muscle, the superior thyroid artery ensures that this muscle can properly function, thereby supporting voice modulation and vocal quality.
Nutrient Delivery and Waste Removal
As with other arteries, the superior thyroid artery plays a key role in delivering oxygen, glucose, and essential nutrients to the tissues it supplies, including the thyroid gland, larynx, and muscles of the neck. It also aids in removing metabolic waste products such as carbon dioxide and lactic acid, ensuring that the tissues remain healthy and functional. This is critical for maintaining the health of the thyroid gland, supporting vocal cord function, and allowing for efficient movement of the muscles in the neck.
Thermoregulation
The superior thyroid artery also helps in thermoregulation by ensuring adequate blood flow to the thyroid gland and surrounding tissues. By regulating the blood flow to these regions, the artery helps maintain the overall temperature of the neck and surrounding areas, especially during periods of increased physical activity or environmental temperature changes.
Contribution to Collateral Circulation
The superior thyroid artery contributes to collateral circulation in the neck, particularly through its anastomoses with the inferior thyroid artery. This anastomotic network ensures that the thyroid gland and other structures receive a consistent and reliable blood supply even if one of the arteries is blocked or compromised. Collateral circulation is important for maintaining tissue health, particularly in cases of vascular occlusion or injury to the arteries in the neck.
Blood Supply to the Cricothyroid Membrane and Surrounding Structures
The cricothyroid branch of the superior thyroid artery supplies blood to the cricothyroid membrane, a key structure located between the thyroid cartilage and cricoid cartilage. This branch helps support the vascularization of the muscles and tissues involved in tension and movement of the vocal cords. By supplying these structures, the artery plays a role in ensuring proper voice modulation and airway function.
Clinical Significance
The superior thyroid artery is clinically important due to its role in supplying blood to the thyroid gland, larynx, and surrounding neck structures. It is commonly encountered in several medical and surgical contexts:
Thyroid Surgery
During thyroidectomy (surgical removal of the thyroid gland), the superior thyroid artery must be carefully identified and ligated to prevent excessive bleeding. Because it supplies the upper part of the thyroid gland, surgeons must be cautious to avoid damaging nearby structures, such as the superior laryngeal nerve, which runs close to the artery and is important for voice function.
Laryngeal Surgeries
In laryngeal surgeries, the superior thyroid artery, through its branch, the superior laryngeal artery, is important for maintaining blood supply to the larynx and vocal cords. Damage to the superior laryngeal artery can compromise vocal cord function and cause post-operative complications such as voice changes or hoarseness.
Vascular Conditions
The superior thyroid artery may be involved in vascular disorders such as aneurysms or arteriovenous malformations (AVMs) in the neck region. Its proximity to major nerves and critical structures makes careful vascular management essential during diagnostic imaging and surgical interventions.
Trauma
Due to its location in the neck, the superior thyroid artery can be damaged in cases of penetrating neck trauma, leading to significant bleeding. Prompt surgical management is required to control hemorrhage and preserve nearby structures.
