The axillary fossa (armpit) is a pyramidal space at the shoulder-chest junction with its base at the skin. Its anterior wall is pectoralis major and minor; posterior wall is subscapularis, latissimus dorsi, and teres major; medial wall is serratus anterior overlying the ribs; lateral wall is the intertubercular groove of the humerus. The apex is the cervicoaxillary canal between the first rib, clavicle, and superior scapula. It contains the brachial plexus cords, the axillary artery and vein, the axillary lymph nodes, and loose fatty areolar tissue.
| Location | Pyramid-shaped space between the upper arm and the side of the chest, below the shoulder joint |
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Acts as the main passageway for vessels, nerves and lymphatics between the neck and the upper limb, with fat that lets them shift as the arm moves. Its lymph nodes drain the arm, breast and upper trunk wall.
The axillary fossa is surgically accessed for axillary lymph node dissection in breast cancer staging and treatment, sentinel node biopsy, axillary artery and vein access, brachial plexus exploration, and thoracodorsal nerve identification for latissimus flap. Axillary lymph nodes are the primary drainage basin for the breast, arm, and lateral chest wall. Axillary node dissection (levels I-III relative to pectoralis minor) risks long thoracic nerve injury (winging), thoracodorsal nerve injury (latissimus weakness), and intercostobrachial nerve injury (axillary numbness).
Axillary lymph node dissection running along the medial axillary wall (serratus anterior) risks injury to the long thoracic nerve supplying serratus anterior from its course on the muscle's surface, producing scapular winging that is cosmetically and functionally disabling, prevented by identifying and protecting the nerve throughout the dissection.
