The Axilla

Key points

• • The axilla is a pyramid-shaped space between the upper arm and the chest wall, through which the main nerves and vessels reach the arm.
• • Its main contents are the axillary artery and vein, the cords and branches of the brachial plexus, and the axillary lymph nodes, all set in fat.
• • The axillary artery is divided into three parts by the pectoralis minor muscle that crosses in front of it.
• • The cords of the brachial plexus are named lateral, medial and posterior by their position around the second part of the axillary artery.
• • The axillary lymph nodes drain the arm and much of the breast, which is why they are assessed in breast cancer, now often first by sentinel lymph-node biopsy rather than routine removal.
• • The long thoracic nerve runs on the chest wall here, and injuring it paralyses serratus anterior, causing a winged scapula.