Axillary neurovascular bundle

Axillary vein (V. axillaris)

The axillary vein is the most superficial element of the entire bundle. Anatomically, it lies immediately beneath the clavipectoral fascia (fascia clavipectoralis). Its pathway originates from beneath the upper margin of the pectoralis minor muscle and runs obliquely in an upward and inward direction. The projection point of this vessel is located precisely 2.5 centimeters medial to the midpoint of the clavicle. In the space between the clavicle and the first rib, the axillary vein continues as the subclavian vein (v. subclavia).

An important clinical feature of the vessel is that its fascial sheath is very tightly fused with the periosteum of the first rib, as well as with the fascia of the subclavius muscle. Due to this fixation, the walls of the vein remain constantly patent and cannot collapse. On the one hand, this rigid fixation greatly simplifies medical venous puncture in this area. On the other hand, in the event of accidental or traumatic injury, there is an extremely high risk of developing life-threatening air embolism. Topographically, throughout its entire length, the vein is always located anterior and medial to the artery and nerve trunks.

Axillary artery (A. axillaris) and its branches

This large arterial trunk runs significantly deeper and more laterally than the vein of the same name. The topography of the artery is traditionally considered in strict accordance with the triangles of the anterior chest wall. For example, within the boundaries of the clavipectoral triangle, two significant branches depart from the main trunk:

• Superior thoracic artery (a. thoracica superior), which branches out and provides blood supply to the first and second intercostal spaces.
• Thoracoacromial artery (a. thoracoacromialis), which divides into three smaller branches almost immediately after its origin.

If the artery and nerves are pulled posteriorly, the sites of origin of other important vessels can be visualized on the posterior wall of the axilla (approximately one centimeter above the tendon of the latissimus dorsi muscle). These include the anterior and posterior circumflex humeral arteries (aa. circumflexae humeri anterior et posterior). The largest branch also originates here — the subscapular artery (a. subscapularis). It runs inferiorly and quickly divides into the circumflex scapular artery (a. circumflexa scapulae), which enters the trilateral space (foramen trilaterum), and the thoracodorsal artery (a. thoracodorsalis), which descends to the inferior angle of the scapula accompanied by the nerve of the same name.

Syntopy of brachial plexus nerves

Within the subpectoral triangle, the nerve trunks are arranged around the axillary artery in a strictly defined manner, forming a kind of sheath. This spatial interrelation is of critical importance during surgeries:

1. Anterior to the artery lies the median nerve (n. medianus). It serves as an excellent internal landmark: the junction of its medial and lateral roots forms a "Y" shape. Directly in the gap between these roots, the pulsating trunk of the axillary artery is visualized.
2. Medially (inward) lie the nerves originating from the medial cord. The largest among them is the ulnar nerve (n. ulnaris). Close to it run the medial cutaneous nerves of the arm and forearm.
3. Laterally (outward) runs the lateral root of the median nerve and the musculocutaneous nerve (n. musculocutaneus). The latter heads directly toward the coracobrachialis muscle and pierces its belly.
4. Posterior to the artery lie the thick branches of the posterior cord — the radial (n. radialis) and axillary (n. axillaris) nerves.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Topography and boundaries of the triangles of the anterior chest wall.
• Anatomy of the trilateral space (foramen trilaterum) and the vessels passing through it.
• The joint course of the posterior circumflex humeral artery and the axillary nerve.
• Detailed composition and branching of the cords of the brachial plexus (plexus brachialis).
• Syntopy of vessels and nerves with the latissimus dorsi and pectoralis minor muscles.

Other topics in the "Upper Extremity" section

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