About 75 per cent to the axillary nodes, most of the rest to the parasternal nodes
Mnemonic
“75 per cent to the axilla”, with the remainder giving the routes that matter for spread:
- Axillary nodes - about 75 per cent, mainly from the lateral quadrants
- Internal mammary (parasternal) nodes - about 20 per cent, from the medial quadrants
- Posterior intercostal nodes, and across the midline to the opposite breast
- Inferior quadrants to the subdiaphragmatic and abdominal nodes
Axillary levels are defined by pectoralis minor:
- Level I - lateral to the muscle
- Level II - behind it
- Level III - medial to it
“Below, behind, beyond.”
Medial quadrant tumours drain to the internal mammary chain, which is not sampled by axillary clearance, and is why a medial tumour can recur with a negative axilla.
Nerves at risk in axillary surgery: the long thoracic (winged scapula), the thoracodorsal (latissimus dorsi weakness) and the intercostobrachial (numbness of the medial upper arm, the commonest and usually accepted).
Expansion
- Axillary nodes - about 75 per cent, mainly from the lateral quadrants
- Parasternal (internal thoracic) nodes - mainly from the medial quadrants
- Posterior intercostal nodes - a small contribution from the deep breast
- Opposite breast and abdominal wall - via superficial lymphatics when normal routes are blocked
Axillary nodes are described in three surgical levels relative to pectoralis minor: level I lateral to it, level II behind it, level III medial to it.
Because the first draining node can be identified and sampled, sentinel node biopsy has largely replaced routine axillary clearance for staging a clinically node-negative axilla.