Pertaining to or located between the azygos vein and esophagus (long hollow muscular tube that connects the pharynx [cavity at the back of the mouth] to the stomach).

The azygos vein is the single vein going up in the abdomen from the right ascending lumbar vein (part of the back between the thorax and the pelvis) or the vena cava (large vein which returns blood to the heart), enters the thorax (between the neck and the abdomen) through the aortic orifice (opening) in the diaphragm, and terminates or ends in the superior vena cava (major blood vessel that returns blood from the head, neck, upper extremities and chest and feeds into the right atrium or thin-walled chamber of the heart which pumps blood into the right ventricle for ejection into the pulmonary or lung circulation).

The region below the azygos vein arch in which the right lung intrudes into the mediastinum (the space in the thoracic cavity behind the sternum and amidst the two pleural sacs containing the lungs) between the heart and the vertebral column, bordered on the left by the esophagus, which is the long hollow muscular tube that connecting the pharynx (cavity at the back of the mouth) to the stomach.