Pertaining to or located between the azygos vein and mediastinum (the region of the chest between the lungs that contains the heart and its large veins and arteries, the trachea [tube that leads from the larynx or voice box to two major air passages that bring oxygen to each lung], the esophagus [tube connecting the throat to the stomach], the bronchi [several large air passages in the lungs through which inhaled air and exhaled air go], and the lymph nodes).

The lymph nodes consist of tissue scattered along the lymphatic system that act as filters and immune monitors, removing fluids, bacteria, or cancer cells that travel through the lymph system.