Subclavian artery

The subclavian artery is a major artery that supplies blood to the arms, neck, thorax, and brain. There are two subclavian arteries, one on each side of the body: the right subclavian artery arises from the brachiocephalic trunk, while the left subclavian artery originates directly from the aortic arch.

Location

The subclavian artery is located deep in the upper thoracic region, running beneath the clavicle (collarbone). It arches laterally over the first rib, passing between the anterior and middle scalene muscles before descending into the axillary region to become the axillary artery. Along its course, the subclavian artery gives rise to important branches, including the vertebral artery, internal thoracic artery, and thyrocervical trunk, which supply the brain, chest wall, and upper limbs. The artery lies close to the brachial plexus, a network of nerves that innervates the upper limb.

Structure and Anatomy

The subclavian artery is a large vessel that supplies blood to the upper limbs, neck, and head, and it is divided into three parts based on its relationship to the anterior scalene muscle. Each part gives rise to specific branches that supply various regions of the body. Below is a detailed description of the anatomy of the subclavian artery.

Origin

The origin of the subclavian artery differs between the right and left sides of the body:

• Right Subclavian Artery: The right subclavian artery originates from the brachiocephalic trunk, which is the first branch off the aortic arch. It arises posterior to the right sternoclavicular joint.
• Left Subclavian Artery: The left subclavian artery arises directly from the aortic arch, to the left of the trachea. Its origin is slightly more distal and posterior compared to the right subclavian artery.

Course and Segments

The subclavian artery is divided into three parts based on its location relative to the anterior scalene muscle:

• First Part: The first part of the subclavian artery extends from its origin to the medial border of the anterior scalene muscle. This section lies deep to the sternocleidomastoid muscle and is positioned superior to the first rib. It gives rise to several major branches in this region, including the vertebral artery, internal thoracic artery, and thyrocervical trunk.
• Second Part: The second part of the subclavian artery lies posterior to the anterior scalene muscle, which separates it from the subclavian vein. In this segment, the artery lies more deeply in the neck and is closely related to the brachial plexus. It gives rise to the costocervical trunk.
• Third Part: The third part of the subclavian artery extends from the lateral border of the anterior scalene muscle to the outer border of the first rib, where it becomes the axillary artery. This section is relatively short and passes through the space between the clavicle and the first rib, known as the scalene triangle.

Relations

• Anteriorly: In the first part, the subclavian artery is covered by the sternocleidomastoid muscle and is crossed by the vagus nerve and phrenic nerve. It lies posterior to the subclavian vein and is separated from it by the anterior scalene muscle. The subclavius muscle and the clavicle are also positioned anterior to the artery.
• Posteriorly: The artery is closely related to the brachial plexus, especially in the second and third parts. The middle scalene muscle lies posterior to the artery as it passes between the scalene muscles.
• Medially: The artery is related medially to the trachea, esophagus, and thoracic duct on the left side.
• Laterally: The third part of the artery is related to the axillary artery and the structures of the upper limb.

Branches

The subclavian artery gives rise to several key branches that supply blood to the brain, neck, chest wall, and upper limbs. These branches arise primarily from the first and second parts of the artery.

From the First Part:

• Vertebral Artery: This artery arises from the first part of the subclavian artery and ascends through the transverse foramina of the cervical vertebrae to supply the posterior part of the brain, including the brainstem and cerebellum.
• Internal Thoracic Artery: This artery descends along the inner aspect of the thoracic wall and supplies the anterior chest wall and diaphragm.
• Thyrocervical Trunk: This is a short trunk that gives rise to the inferior thyroid artery, transverse cervical artery, and suprascapular artery, which supply the thyroid gland, neck muscles, and scapular region.

From the Second Part:

Costocervical Trunk: The costocervical trunk arises from the second part of the subclavian artery and divides into the deep cervical artery, which supplies the deep muscles of the neck, and the supreme intercostal artery, which supplies the first two intercostal spaces.

From the Third Part:

Dorsal Scapular Artery: In some individuals, the dorsal scapular artery arises from the third part of the subclavian artery. It supplies the rhomboid muscles and the medial border of the scapula. In other cases, it may originate from the thyrocervical trunk.

Termination

The subclavian artery terminates at the lateral border of the first rib, where it becomes the axillary artery. The axillary artery supplies the upper limb and continues as the brachial artery further down the arm.

Anastomoses

The subclavian artery forms several important anastomoses with other arteries:

• The vertebral artery anastomoses with the internal carotid system via the Circle of Willis, ensuring collateral circulation to the brain.
• The internal thoracic artery forms anastomoses with the intercostal arteries and superior epigastric artery.
• The branches of the thyrocervical trunk anastomose with arteries supplying the scapular and neck regions, providing collateral circulation to the shoulder and neck.

Variations

Anatomical variations in the origin and course of the subclavian artery are relatively common. For example, the right subclavian artery can arise directly from the aortic arch in cases where the brachiocephalic trunk is absent. The branches of the subclavian artery can also vary, with the dorsal scapular artery sometimes arising from the thyrocervical trunk rather than the third part of the subclavian artery.

Function

The subclavian artery serves as the primary artery supplying oxygenated blood to the upper limbs, neck, thorax, and parts of the brain. Through its various branches, it ensures that critical regions receive the blood supply necessary for proper function. Below is a detailed explanation of its specific functions.

Blood Supply to the Upper Limb

One of the main functions of the subclavian artery is to provide blood to the upper limb. As the artery continues beyond the lateral border of the first rib, it becomes the axillary artery, which supplies the shoulder and arm with oxygenated blood. From the axillary artery, the blood flows into the brachial artery to supply the forearm, wrist, and hand.

Axillary Artery: The transition of the subclavian artery into the axillary artery marks its major role in upper limb perfusion. The axillary artery and its branches nourish the muscles, bones, and connective tissues of the shoulder, arm, and hand.

Blood Supply to the Brain (via Vertebral Artery)

Another key function of the subclavian artery is to provide blood to the posterior part of the brain, including the brainstem, cerebellum, and occipital lobes, through its branch, the vertebral artery.

Vertebral Artery: The vertebral artery is a major branch of the subclavian artery. It ascends through the transverse foramina of the cervical vertebrae and enters the cranial cavity through the foramen magnum. The vertebral arteries from both sides merge to form the basilar artery, which supplies the posterior circulation of the brain, including the brainstem and cerebellum. The vertebral artery’s contribution to the Circle of Willis also ensures collateral circulation, providing an alternative route for blood to reach the brain if other pathways are compromised.

Blood Supply to the Thoracic Wall and Diaphragm (via Internal Thoracic Artery)

The subclavian artery provides blood to the anterior thoracic wall and the diaphragm through the internal thoracic artery, which descends along the inner surface of the thoracic wall.

Internal Thoracic Artery: This artery supplies the intercostal muscles, sternum, and thoracic wall. It also gives off branches, such as the anterior intercostal arteries, which provide blood to the muscles and skin of the chest. Additionally, the internal thoracic artery continues downward to supply the diaphragm through its branches, the musculophrenic artery and superior epigastric artery. These arteries are essential for supporting the diaphragm’s function in respiration.

Blood Supply to the Neck and Thyroid Gland (via Thyrocervical Trunk)

The subclavian artery supplies blood to the neck, thyroid gland, and scapular region via the thyrocervical trunk.

Thyrocervical Trunk: This trunk gives rise to several arteries that supply the neck and thyroid gland. The inferior thyroid artery is a major branch of the thyrocervical trunk, which supplies the thyroid gland and the parathyroid glands. The transverse cervical artery and suprascapular artery are other branches that supply muscles in the neck and upper back, including the trapezius and the muscles around the scapula.

Blood Supply to the Deep Neck and Upper Intercostal Spaces (via Costocervical Trunk)

The subclavian artery, through its costocervical trunk, provides blood to the deep structures of the neck and the upper intercostal spaces.

Costocervical Trunk: The costocervical trunk arises from the second part of the subclavian artery and branches into the deep cervical artery, which supplies the deep muscles of the neck, and the supreme intercostal artery, which provides blood to the first two intercostal spaces. These arteries ensure that the neck muscles and upper chest receive an adequate blood supply, supporting activities such as breathing, posture, and movement.

Blood Supply to the Scapular Region (via Dorsal Scapular Artery)

In some individuals, the subclavian artery gives rise to the dorsal scapular artery, which supplies blood to the scapular region.

Dorsal Scapular Artery: This artery supplies the rhomboid muscles and the levator scapulae. It travels along the medial border of the scapula and helps form anastomoses with other arteries in the shoulder and back, such as the suprascapular artery and circumflex scapular artery. This blood supply is critical for maintaining the function and strength of the muscles that move and stabilize the shoulder blade.

Contribution to Collateral Circulation

The subclavian artery plays a significant role in collateral circulation by forming important anastomoses between its branches and other arteries, ensuring that blood flow can be rerouted in the event of blockages or arterial damage.

• Vertebral Artery and Circle of Willis: The vertebral artery, as part of the Circle of Willis, ensures collateral circulation to the brain, allowing blood to flow between the anterior and posterior circulations of the brain. This is crucial in preventing ischemic events in the brain.
• Scapular Anastomoses: The dorsal scapular artery and suprascapular artery form part of the scapular anastomotic network, providing collateral blood flow to the shoulder and upper back.

Support for Thoracic and Abdominal Structures

Through its branches, such as the internal thoracic artery and superior epigastric artery, the subclavian artery ensures blood supply to thoracic and upper abdominal structures.

Anterior Thoracic Wall and Diaphragm: The internal thoracic artery and its branches, the musculophrenic and superior epigastric arteries, supply the anterior thoracic wall and diaphragm. This is important for breathing, chest wall movement, and overall thoracic stability.

Clinical Significance

The subclavian artery is of great clinical significance because it supplies blood to the upper limbs, neck, brain, and parts of the thoracic region. Its branches, such as the vertebral artery and internal thoracic artery, are crucial for providing oxygenated blood to the brain and chest. Any obstruction, injury, or disease affecting the subclavian artery can have severe consequences, such as subclavian steal syndrome, where blood flow is redirected from the brain to the arm due to a blockage. This can cause symptoms like dizziness, visual disturbances, and arm weakness.

The subclavian artery is also involved in conditions such as thoracic outlet syndrome, where compression of the artery between the scalene muscles and first rib results in reduced blood flow to the arm. It is important in surgical procedures, including coronary artery bypass grafting (CABG), where the internal thoracic artery (a branch of the subclavian) is often used to bypass blocked coronary arteries. Understanding its anatomy is vital for interventions in trauma, vascular surgeries, and diagnosis of vascular disorders.