In the posterior mediastinum the nodes are arranged in series with those of the abdomen. The visceral preaortic nodes lie in front of the aorta and drain the middle reaches of the esophagus. The somatic para-aortic nodes lie alongside the aorta and extend laterally into the posterior intercostal spaces, where they are known as the posterior intercostal nodes. They drain the intercostal spaces. The anterior ends of the intercostal spaces drain into parasternal nodes along the internal thoracic artery; they may become involved in cancer of the breast, and drain directly into the brachiocephalic veins.
The lower members of the parasternal group lie on the diaphragm between pericardium and xiphoid process (anterior diaphragmatic nodes). The lower members of the para-aortic group in the posterior mediastinum likewise lie on the diaphragm forming the posterior diaphragmatic group. In addition a middle diaphragmatic group lies on each dome of the diaphragm; they drain from the extraperitoneal areolar tissue beneath the diaphragm and, on the right side, from the superficial part of the bare area of the liver.
The upper members of the posterior intercostal group drain into the thoracic duct or into the right lymphatic duct; the lower (intercostal and diaphragmatic) members drain into a descending intercostal trunk that passes downwards to join the cisterna chyli in the aortic opening of the diaphragm.
Heart and lungs drain into the tracheobronchial lymph nodes, which lie around the trachea and its bifurcation. These send their efferents to a right and left mediastinal lymph trunk, which may join the thoracic duct but usually open directly into the brachiocephalic vein of their own side.
There are thus three up going lymph channels on each side, namely the parasternal alongside the sternum, the thoracic duct and right lymphatic duct alongside the vertebrae (these drain the thoracic wall) and between them the mediastinal lymph trunks alongside the trachea (these drain lungs, mid-part of esophagus, and heart). All six trunks communicate freely with each other.