The Anatomy of the Axillary Vein

The axillary vein is a major vein in the upper body that carries blood from the upper limb, armpit, and the upper side of the chest wall towards the heart. On each side of the body, it forms where the basilic and brachial veins join in the axilla, a space just below the shoulder that allows arteries, veins, and nerves to pass.

Its course is relatively short as it moves upwards towards the middle of the body and terminates into the subclavian vein at the border of the first (topmost) rib.

As a deep vein that plays a critical role in upper body circulation, diseases or disorders of the axillary vein can become problematic. In particular, axillary thrombosis—a kind of deep vein thrombosis (DVT), or blood clotting—is a relatively rare, but potentially very dangerous condition.

This vein may also sometimes be considered as a means to gain venous access for the placement of a pacemaker, though it’s a riskier alternative.

Anatomy

Structure

The body has an axillary vein on each side, typically varying between 1.1 and 1.2 centimeters (cm) in diameter. Veins are typically a little thinner than arteries, which are the vessels that carry blood away from the heart. They consist of three layers:

• Tunica intima: The inner lining of veins is composed of a layer of flat cells, called squamous epithelium, in contact with a base membrane that keeps blood inside.
• Tunica media: The middle layer of veins is smooth muscle, which can apply pressure on the axillary vein to push blood along and help regulate function.
• Tunica adventita: This thicker, outer layer has elastic fibers that help connect vessels to surrounding tissues for support.  

Location

The axillary vein arises at the lower border of the axilla, just beneath the teres major shoulder muscle, near where the underarm meets the body. Along its course are several important features:

• Origin: The basilic vein, a primary surface (“superficial”) vein of the arm, and the brachial vein, one of the upper arm’s deep veins, join together to form the axillary vein. 
• Axillary region: The axillary vein travels upwards and towards the middle of the body, crossing the armpit. As it does so, it runs close to the axillary artery along with a bundle of nerves, including the lateral and medial pectoral nerves, the brachial plexus, and the ulnar nerve.
• Termination: As it crests to the top of the axilla space, another major vein of the arm, the cephalic vein, joins up, and the two terminate into the subclavian vessel. This occurs at the border of the top-most rib.

In addition to the cephalic vein, the axillary vein has several other tributaries, which correspond to branches of the axillary artery. These are:

• Thoracoacromial vein
• Lateral thoracic vein
• Subscapular vein
• Anterior circumflex
• Humeral vein
• Posterior circumflex humeral vein

Anatomical Variations

Congenital differences in the anatomy of the axillary vein are relatively common, and many people will display small variations. In particular, accessory axillary vein, in which a small, second vein arises alongside the primary one, may occur in over half the population. The specific position of this second vein varies a great deal, and it may join

In addition, doctors have observed different origins for the axillary vein, as the brachial and basilic veins may meet at different positions. Furthermore, the cephalic vein—usually joining near to the end of the axillary vein’s course—may also run into it earlier along.

Function

The circulatory system’s main job is to deliver oxygen from the lungs to the rest of the body. Blood cells are laden with oxygen in the heart and then pumped out through the arteries. In turn, it’s the veins that bring deoxygenated blood back.

Given its position in the body, the axillary vein conveys blood from the axilla, the side of the chest cavity (thorax), and the upper arm.

Clinical Significance

Clinically speaking, there are a couple cases where the axillary vein comes into play.

Cannulation

This vein may be considered for cannulation, which means inserting a tube or catheter. Most often, this technique is employed as means to implant a pacemaker near the heart using a minimally-invasive procedure. The axillary vein will be considered in cases where employing other veins is likely to be dangerous.

Axillary Vein Thrombosis

Blood clotting of the axillary vein is relatively rare in the general population, though it occurs more often in competitive athletes. Repeated strain, injury, or other factors this condition, which leads to swelling, blue color, heaviness, and pain in the arm.

If untreated, this condition can lead to pulmonary embolism (blood clot in the lung), stroke, heart failure, and venous insufficiency, among other dangerous conditions. Blood-thinning medications, physical therapy, as well as surgeries, resolve this condition.