Learning Objectives
Understand the anatomy of the axilla, including its borders, contents, passageways, and clinical significance, to identify its role as a major conduit for neurovascular and muscular structures of the upper limb.
Introduction to the Axilla
The axilla (armpit) is a pyramidal-shaped space situated beneath the glenohumeral joint. It acts as the gateway between the neck/thorax and the upper limb.
1. Structure and Borders
The axilla is defined by six boundaries. Understanding these is essential for surgical oncology and regional anesthesia.
| Border | Anatomical Boundaries |
|---|---|
| Apex (Inlet) | Lateral border of 1st rib, superior scapula, and posterior clavicle. |
| Anterior Wall | Pectoralis major, Pectoralis minor, and Subclavius. |
| Posterior Wall | Subscapularis, Teres major, and Latissimus dorsi. |
| Medial Wall | Serratus anterior and the upper ribs. |
| Lateral Wall | Intertubercular (bicipital) groove of the humerus. |
| Base (Floor) | Axillary fascia and skin of the armpit. |
2. Contents of the Axilla
The axilla contains vital neurovascular structures embedded in axillary fat.
| Structure | Key Clinical Feature |
|---|---|
| Axillary Artery | Divided into 3 parts by the pectoralis minor muscle. |
| Axillary Vein | Located medial to the artery; receives the cephalic and basilic veins. |
| Brachial Plexus | Cords and terminal branches (e.g., Median, Ulnar, Radial nerves). |
| Lymph Nodes | Arranged in 5 groups; primary drainage for 75% of breast tissue. |
3. Passageways (Exits)
Structures leave the axilla via specific anatomical “doorways” to reach the posterior shoulder or anterior chest.
| Passageway | Transmitted Structures |
|---|---|
| Quadrangular Space | Axillary nerve and Posterior circumflex humeral artery. |
| Clavipectoral Triangle | Cephalic vein, Thoracoacromial artery, Lateral pectoral nerve. |
4. Clinical Relevance
High-Yield Clinical Pearls:
- Thoracic Outlet Syndrome (TOS): Compression at the Apex. Can be caused by a cervical rib or Pancoast tumor, leading to wasting of intrinsic hand muscles (T1).
- Winged Scapula: Damage to the Long Thoracic Nerve (C5-C7) during axillary clearance. This paralyzes the Serratus Anterior.
- Breast Cancer: Axillary lymph nodes are the first site of metastasis for most breast cancers.