Where the lymph of the breast drains

Lymph is the fluid the body collects from the tissues and returns to the blood, and the lymph of the breast follows a fairly set route: in about three out of four cases it heads toward the lymph nodes in the armpit. In most cases the traffic exits through the armpit.

Before leaving, the lymphatic channels come together under the areola, the dark circle around the nipple, and there they form a network with a name of its own: Sappey's plexus.

In the armpit those nodes are not jumbled together. They are organized into three levels according to where they sit in relation to the pectoralis minor, a small muscle of the shoulder: lateral, posterior and medial to it.

The armpit is not the only exit. In about one in twenty cases the node in charge is the internal mammary node, tucked under the breastbone, the bone in the center of the chest. And in the remaining quarter of cases drainage is split between the two routes at once.