Describe the boundaries and contents of the axilla. Add a note on the axillary artery and the axillary lymph nodes.

Definition

Boundaries

• The anterior fold is formed by the lower border of pectoralis major; the posterior fold by latissimus dorsi and teres major

Contents

• Axillary artery and its branches
• Axillary vein and its tributaries
• Cords and branches of the brachial plexus
• Axillary lymph nodes — five groups
• Long thoracic nerve (on serratus anterior) and intercostobrachial nerve
• Axillary fat and areolar tissue
• The axillary tail of Spence of the breast pierces the deep fascia to enter the axilla

Axillary Artery

• Continuation of the subclavian artery at the outer border of the first rib; becomes the brachial artery at the lower border of teres major
• Divided into three parts by pectoralis minor — a useful rule: the number of branches equals the number of the part

• The subscapular artery is the largest branch
• The posterior circumflex humeral artery passes through the quadrangular space with the axillary nerve

Axillary LYMPH Nodes

Clavipectoral Fascia

• A strong sheet extending from the clavicle above to the axillary fascia below, enclosing subclavius and pectoralis minor
• Structures piercing it — mnemonic "LCTC":Lateral pectoral nerve
• Cephalic vein
• Thoraco-acromial artery
• Cephalic lymphatics
• Its lower part is the suspensory ligament of the axilla, which holds the axillary fascia up and produces the hollow of the armpit

Axillary Vein and Nerve Relations

• The axillary vein is formed by the union of the basilic vein and the venae comitantes of the brachial artery, at the lower border of teres major
• It lies medial and anterior to the artery, and becomes the subclavian vein at the outer border of the first rib
• The cephalic vein ends in it after piercing the clavipectoral fascia
• The vein is a common site for central venous access, and its wall is held open by fascia, so a tear can cause air embolism
• The three cords surround the second part of the artery, which is how they are named; the median nerve is formed in front of the third part

Applied Aspects

• Axillary lymph node clearance in breast carcinoma risks injury to the long thoracic nerve (winged scapula) and the thoracodorsal nerve, and causes lymphoedema of the arm
• Sentinel node biopsy has largely replaced routine clearance, sparing these complications
• Axillary abscess must be drained through the medial wall, to avoid the vessels and nerves laterally
• The axillary artery can be compressed against the humerus in the lateral wall to control bleeding
• Intercostobrachial nerve injury causes numbness over the medial arm after axillary surgery — a common and often unwarned complaint