The thyrocervical trunk is a short, thick arterial branch that arises from the first part of the subclavian artery. It is a key vessel that gives rise to several important branches, including the inferior thyroid artery, transverse cervical artery, suprascapular artery, and sometimes the ascending cervical artery.
Location
The thyrocervical trunk originates from the first part of the subclavian artery, which is located just medial to the anterior scalene muscle in the lower neck. It arises near the base of the neck, typically posterior to the clavicle. The trunk ascends for a short distance before dividing into its branches, which extend toward the thyroid gland, cervical spine, and scapular region. These branches supply blood to the thyroid, neck muscles, and shoulder region. The thyrocervical trunk is located anterior to the vertebral artery and is positioned close to the phrenic nerve.
Anatomy
Origin
The thyrocervical trunk arises from the first part of the subclavian artery, which is located just medial to the anterior scalene muscle. The subclavian artery itself arises from the aortic arch on the left side and from the brachiocephalic trunk on the right side. The thyrocervical trunk is one of several branches that emerge from the first part of the subclavian artery, along with the vertebral artery and internal thoracic artery.
Course
The thyrocervical trunk has a short, upward course. It ascends almost vertically from the subclavian artery and lies anterior to the vertebral artery. It quickly divides into its major branches, which extend toward various regions of the neck, thyroid, and scapula. The trunk’s location is just medial to the anterior scalene muscle, close to the root of the neck, and posterior to the clavicle.
Relations
- Anteriorly: The thyrocervical trunk lies deep to the sternocleidomastoid muscle and is anterior to the anterior scalene muscle. It also runs near the phrenic nerve, which passes anteriorly across the trunk as it descends toward the diaphragm.
- Posteriorly: It is related to the vertebral artery, which courses upward toward the transverse foramina of the cervical vertebrae.
- Medially: It is located near the subclavian artery and the origin of the vertebral artery.
- Laterally: It is positioned close to the anterior scalene muscle, which separates it from other neurovascular structures in the neck, such as the brachial plexus.
Branches
The thyrocervical trunk quickly divides into three or four main branches, which supply different regions of the neck, thyroid, and scapula. These branches include:
- Inferior Thyroid Artery: This is the largest and most important branch of the thyrocervical trunk. It ascends medially toward the thyroid gland, passing behind the carotid sheath to supply the thyroid gland, parathyroid glands, trachea, esophagus, and surrounding tissues.
- Transverse Cervical Artery: This branch courses laterally across the neck, passing anterior to the scalenes and phrenic nerve. It supplies blood to the trapezius and rhomboid muscles, and in some cases, it gives rise to the dorsal scapular artery, which supplies the medial border of the scapula.
- Suprascapular Artery: The suprascapular artery travels laterally, passing above the superior transverse scapular ligament and providing blood to the supraspinatus and infraspinatus muscles. It crosses above the clavicle and toward the scapular notch.
- Ascending Cervical Artery (when present): This branch ascends along the cervical spine, supplying the deep muscles of the neck and contributing to the vascularization of the spinal cord and surrounding structures.
Termination
The thyrocervical trunk terminates shortly after giving rise to its branches, which spread to different regions of the neck, shoulder, and thyroid. The trunk itself is quite short and does not have a long independent course, as it rapidly divides into its arteries.
Anastomoses
Several branches of the thyrocervical trunk form important anastomoses with other arteries in the neck and shoulder region:
- The inferior thyroid artery anastomoses with the superior thyroid artery, ensuring a robust blood supply to the thyroid gland.
- The transverse cervical artery anastomoses with the suprascapular artery and other branches in the scapular region, contributing to the scapular anastomotic network.
- The ascending cervical artery may form small anastomoses with branches of the vertebral artery or deep cervical artery, ensuring vascularization to the cervical spine and spinal cord.
Variations
There is considerable anatomical variation in the branching patterns of the thyrocervical trunk. In some cases, the dorsal scapular artery may arise directly from the thyrocervical trunk, or it may originate from the transverse cervical artery. Additionally, the size and course of the individual branches, particularly the ascending cervical artery, can vary between individuals. These variations are important to note during surgical procedures in the neck and shoulder region.
Function
The thyrocervical trunk plays a crucial role in providing blood supply to the thyroid gland, neck muscles, and scapular region. Through its various branches, it ensures that key structures in the neck and upper back receive the oxygen and nutrients they need for proper functioning. Each branch of the thyrocervical trunk serves a specific area, making it a vital part of the vascular system in the cervical and upper thoracic regions.
Blood Supply to the Thyroid Gland
One of the primary functions of the thyrocervical trunk is to supply blood to the thyroid gland through the inferior thyroid artery, which is its largest branch. The thyroid gland, located in the anterior part of the neck, is responsible for regulating metabolism and producing hormones critical for the body’s energy balance. The inferior thyroid artery ascends medially toward the gland, providing blood to the inferior and posterior portions of the thyroid, as well as to the adjacent parathyroid glands, trachea, and esophagus. This arterial supply is essential for maintaining thyroid function and hormone production, as the gland requires a rich blood flow to support its metabolic activity.
Blood Supply to the Neck Muscles
The thyrocervical trunk, through its transverse cervical artery and ascending cervical artery, supplies the deep and superficial muscles of the neck. These muscles are essential for various movements of the head, neck, and shoulders, including flexion, extension, and rotation. The transverse cervical artery provides blood to the trapezius muscle, which is involved in scapular elevation, retraction, and rotation, and may also contribute to the supply of the rhomboid muscles and levator scapulae if it gives rise to the dorsal scapular artery.
The ascending cervical artery, when present, supplies the deep muscles of the neck, including the scalene muscles and muscles surrounding the cervical vertebrae. This artery also sends branches to the spinal cord and its coverings (meninges), ensuring that the cervical part of the spinal cord receives sufficient blood supply for its vital functions.
Blood Supply to the Shoulder and Scapula
The thyrocervical trunk’s suprascapular artery is responsible for supplying blood to the supraspinatus and infraspinatus muscles, which are part of the rotator cuff. These muscles are essential for the stability and movement of the shoulder joint, particularly in arm elevation, rotation, and abduction. The suprascapular artery travels laterally, passing above the superior transverse scapular ligament and into the supraspinous fossa, where it nourishes the muscles of the scapula. Proper blood flow to these muscles ensures their functionality and endurance during activities that require shoulder mobility and strength.
In addition to supplying these muscles, the suprascapular artery also plays a role in maintaining collateral circulation around the scapula by forming anastomoses with the circumflex scapular artery and other nearby arteries. This collateral network is critical in maintaining blood flow to the scapular region, particularly in cases of vascular injury or occlusion.
Support for Collateral Circulation
An important function of the thyrocervical trunk is its role in forming anastomoses with other arteries in the neck, thyroid, and scapular regions, providing collateral circulation. This redundancy in blood supply ensures that, in cases of occlusion or damage to one artery, the blood flow to critical structures remains uninterrupted.
For example, the inferior thyroid artery forms anastomoses with the superior thyroid artery, which arises from the external carotid artery. This connection ensures a continuous blood supply to the thyroid gland, even if one of the arteries becomes compromised. Similarly, the suprascapular artery and transverse cervical artery form anastomoses with the circumflex scapular artery and dorsal scapular artery, creating a network of arteries that provide blood flow to the scapular region, particularly in cases of trauma or vascular surgery.
Vascularization of the Spinal Cord and Meninges
The ascending cervical artery, when present, plays an essential role in supplying the cervical portion of the spinal cord and its surrounding meninges. This is crucial for maintaining the health and functionality of the spinal cord, which transmits nerve signals between the brain and the rest of the body. The artery ensures that the spinal cord and its protective coverings receive adequate oxygen and nutrients, which is particularly important in preventing spinal cord ischemia or injury.
Nutrient Supply to the Esophagus and Trachea
In addition to its main branches, the inferior thyroid artery provides small branches to the esophagus and trachea in the neck region. These structures rely on a consistent blood supply to maintain their function as part of the respiratory and digestive systems. The esophagus, which carries food to the stomach, and the trachea, which conducts air to the lungs, both require vascular support to sustain their structural integrity and function. By supplying blood to these tissues, the inferior thyroid artery ensures that the upper respiratory and digestive tracts remain healthy.
Support for Tissue Healing and Regeneration
The thyrocervical trunk plays a vital role in supporting tissue healing and regeneration in the neck and upper thoracic regions. Its rich vascular supply to the thyroid gland, neck muscles, and scapular region is essential for repairing tissues after injury, surgery, or inflammation. The blood delivered by the thyrocervical trunk helps transport oxygen, nutrients, and immune cells that are necessary for healing processes, ensuring faster recovery and maintaining the health of the tissues.
Clinical Significance
The thyrocervical trunk is clinically significant due to its role in supplying blood to critical structures in the neck, thyroid gland, and upper back. Its branches, such as the inferior thyroid artery, transverse cervical artery, and suprascapular artery, provide vital blood flow to the thyroid gland, parathyroid glands, trachea, esophagus, neck muscles, and scapular region.
In thyroid surgeries (e.g., thyroidectomy), careful management of the inferior thyroid artery is crucial to avoid complications such as excessive bleeding or damage to the recurrent laryngeal nerve, which can result in voice changes or vocal cord paralysis. Injury to the artery can also lead to compromised blood flow to the thyroid and parathyroid glands, causing hypocalcemia and other metabolic issues.
In shoulder surgeries or trauma cases involving the scapula or neck, understanding the anatomy of the thyrocervical trunk’s branches is essential to avoid vascular injury. Its branches also form part of the collateral circulation in the shoulder and neck region, which is important in maintaining blood flow during arterial occlusions or surgical interventions.
