Axillary vein

The axillary vein is a large vein located in the axilla (armpit region) that serves as a major conduit for venous return from the upper limb. It is formed by the union of the brachial veins and the basilic vein at the lower border of the teres major muscle. The axillary vein runs alongside the axillary artery but lies more superficially. As it ascends through the axilla, it receives blood from several tributaries, including the cephalic vein, subscapular vein, and thoracoacromial vein. The vein continues its course until it reaches the lateral border of the first rib, where it transitions into the subclavian vein.

Structure and Anatomy

Location

The axillary vein is located in the axilla (armpit region) and runs from the lower border of the teres major muscle to the lateral border of the first rib, where it transitions into the subclavian vein. It lies anterior and slightly medial to the axillary artery, with the artery being positioned deeper within the axillary space. The axillary vein serves as the major venous pathway for the upper limb, running from the lower arm through the axilla to the shoulder region.

Origin

The axillary vein is formed by the convergence of the brachial veins (venae comitantes of the brachial artery) and the basilic vein. This union occurs near the lower border of the teres major muscle. The basilic vein, a large superficial vein from the medial side of the arm, contributes to this venous confluence. The brachial veins are paired deep veins that drain the upper arm and accompany the brachial artery.

Course

The axillary vein runs superiorly through the axillary region, following a more superficial course compared to the axillary artery. It begins at the lower border of the teres major muscle and ascends toward the shoulder. As it passes through the axilla, it receives several tributaries that drain the upper limb, shoulder, and thoracic region. The vein continues its upward course until it reaches the lateral border of the first rib, at which point it transitions into the subclavian vein.

Relations

• Anterior relations: The axillary vein is covered by the skin, subcutaneous tissue, and fascia of the axillary region. Superficial to the vein are the lymph nodes and fat of the axilla.
• Posterior relations: Posterior to the axillary vein are the axillary artery and the brachial plexus, which are key structures in the axilla. The axillary artery is deeper and slightly more lateral than the vein.
• Lateral relations: The axillary vein is bordered laterally by the pectoralis major and pectoralis minor muscles, which form part of the anterior wall of the axilla.
• Medial relations: Medially, the vein is adjacent to the thoracic wall, which includes the serratus anterior muscle and the ribs.

Tributaries

The axillary vein receives blood from several important tributaries as it ascends through the axillary region:

• Basilic vein: A superficial vein from the medial aspect of the arm that contributes to the formation of the axillary vein.
• Cephalic vein: A large superficial vein from the lateral aspect of the arm that drains into the axillary vein near the deltopectoral groove.
• Subscapular vein: Drains blood from the muscles around the scapula, including the subscapularis, teres major, and latissimus dorsi muscles.
• Thoracoacromial vein: Drains the chest wall and shoulder region, including areas supplied by the thoracoacromial artery.
• Lateral thoracic vein: Drains the lateral chest wall and breast tissue.
• Thoracodorsal vein: A tributary of the subscapular vein that drains the latissimus dorsi muscle.

Termination

The axillary vein terminates at the lateral border of the first rib, where it becomes the subclavian vein. At this point, the vein transitions from the axillary region to the base of the neck, continuing the pathway for venous return from the upper limb toward the central venous system.

Surrounding Structures

• Anteriorly: The vein is related to the skin, fascia, and superficial tissues of the axilla. The pectoralis major and pectoralis minor muscles are located anterior to the vein.
• Posteriorly: The axillary artery and brachial plexus lie deeper and posterior to the axillary vein. These structures are critical for arterial blood supply and innervation to the upper limb.
• Laterally: The humerus and coracobrachialis muscle are located lateral to the axillary vein.
• Medially: Medial to the vein are the thoracic wall, including the serratus anterior muscle and the ribs, which form part of the medial wall of the axilla.

Variations

The anatomy of the axillary vein can exhibit anatomical variations in size, course, and tributary patterns. In some individuals, the position of the axillary vein relative to the axillary artery may vary slightly, with the vein sometimes being more anterior or medial. Variations in the size and prominence of the tributaries, such as the cephalic and basilic veins, are also common. In rare cases, additional venous channels may drain into the axillary vein or bypass the normal venous routes, leading to anatomical diversity in the venous drainage system of the upper limb and thorax.

Function

Venous Drainage of the Upper Limb

The primary function of the axillary vein is to drain venous blood from the upper limb, including the arm, forearm, and hand. It collects deoxygenated blood from both the deep and superficial venous systems of the upper limb, ensuring that venous return from the entire upper extremity is directed toward the central venous circulation. The axillary vein receives blood from the deep veins, such as the brachial veins, and from superficial veins like the basilic and cephalic veins, which drain the skin, muscles, and subcutaneous tissues of the upper arm and forearm.

Confluence of Superficial and Deep Veins

The axillary vein serves as a crucial connection point for both superficial and deep venous systems of the upper limb. It is formed by the union of the brachial veins (deep veins that accompany the brachial artery) and the basilic vein (a superficial vein). Additionally, it receives the cephalic vein, another major superficial vein that drains the lateral side of the arm. By facilitating venous return from both deep and superficial venous systems, the axillary vein helps maintain efficient circulation throughout the arm and ensures that blood from various regions is returned to the heart.

Venous Return from the Shoulder Region

The axillary vein plays an important role in draining venous blood from the shoulder region, including the scapular muscles, deltoid, and pectoral regions. Through its tributaries, such as the subscapular vein, thoracoacromial vein, and lateral thoracic vein, the axillary vein collects blood from the muscles and soft tissues of the shoulder and upper chest. This venous return is essential for ensuring efficient circulation in the shoulder and surrounding structures, especially during physical activities that involve shoulder movement and arm elevation.

Connection with the Thoracic Venous System

The axillary vein also facilitates venous return from the thoracic wall and adjacent areas. The lateral thoracic vein, which drains the lateral chest wall and breast, and the thoracodorsal vein, which drains the latissimus dorsi muscle, both feed into the axillary vein. By collecting blood from these tributaries, the axillary vein supports venous return from the thoracic wall and upper back, maintaining overall circulation in these regions. This connection with the thoracic venous system is important for ensuring the proper drainage of blood from the upper body.

Pathway for Venous Return to the Heart

The axillary vein functions as a critical pathway for venous return to the heart. After collecting blood from the upper limb, shoulder, and thoracic region, the axillary vein continues its course superiorly and transitions into the subclavian vein at the lateral border of the first rib. The subclavian vein eventually drains into the brachiocephalic vein, which leads to the superior vena cava, and finally into the right atrium of the heart. This pathway is essential for returning deoxygenated blood from the upper body to the heart, where it can be oxygenated and circulated through the body again.

Role in Venous Return During Upper Limb Movements

The axillary vein supports venous return during upper limb movements, especially during activities that involve the shoulder, arm, or hand. The muscles of the upper limb, including the biceps brachii, deltoid, and pectoral muscles, assist in venous return through the muscle pump mechanism. When these muscles contract, they compress nearby veins, including the axillary vein, helping push venous blood back toward the heart. This muscle pump action is crucial for overcoming the effects of gravity, particularly when the arm is elevated, and it ensures that venous blood from the upper limb is efficiently returned to the central circulation.

Regulation of Venous Pressure

The axillary vein plays a key role in regulating venous pressure in the upper limb and thoracic region. By acting as a major conduit for venous blood, it helps balance pressure between the superficial and deep venous systems. If there is increased pressure in one region, such as the cephalic or basilic veins, the axillary vein helps redistribute blood, preventing venous congestion. This regulation of pressure is essential for maintaining smooth venous return, particularly during physical activity or changes in body position.

Drainage of Venous Blood from the Pectoral and Scapular Muscles

The axillary vein also drains venous blood from the pectoral and scapular muscles through its tributaries. The thoracoacromial vein collects blood from the pectoral region, including the pectoralis major and pectoralis minor muscles, while the subscapular vein drains the muscles around the scapula, including the teres major, teres minor, and subscapularis muscles. This drainage ensures that the metabolic waste products produced by these muscles are removed and transported to the central venous system for processing.

Facilitation of Lymphatic Drainage

Though not directly part of the lymphatic system, the axillary vein is closely associated with the axillary lymph nodes and plays an indirect role in supporting lymphatic drainage. The lymphatic vessels in the axillary region drain lymph from the upper limb, breast, and thoracic wall, and they converge near the axillary vein. The vein’s proximity to these lymphatic structures allows for the coordinated removal of both venous blood and lymphatic fluid, ensuring proper circulation and immune function in the upper limb and chest.

Thermoregulation

The axillary vein contributes to thermoregulation by facilitating the removal of heat from the upper limb and shoulder. During physical activity or exposure to warm environments, increased blood flow through the axillary vein helps dissipate heat from the muscles and skin, allowing the body to maintain a stable internal temperature. By transporting warm venous blood from the upper limb to the heart, the axillary vein aids in cooling the body during periods of increased heat production.

Clinical Significance

The axillary vein is clinically significant due to its role in central venous access and its proximity to key anatomical structures. It is often used in central venous catheterization, particularly for long-term intravenous therapies, dialysis access, or when other venous routes are unavailable. Its superficial location in the axilla makes it relatively accessible, but care must be taken to avoid damage to surrounding structures, including the axillary artery and the brachial plexus.

The axillary vein is also important in axillary lymph node dissection, commonly performed during breast cancer surgery. Surgeons must be cautious to avoid injury to the vein during such procedures, as damage can lead to complications like bleeding, venous thrombosis, or lymphedema.

Trauma or compression in the axillary region can result in axillary vein thrombosis or deep vein thrombosis (DVT) of the upper limb, leading to symptoms such as arm swelling and pain. Understanding the anatomy and clinical implications of the axillary vein is crucial in diagnosing and managing vascular conditions affecting the upper limb.