Azygos Vena

AZYGOS VENA (from the Greek a- negative particle and zygos - yoke), the azygos vein, a term given by Galen to this vein, which does not accompany an artery (Hyrtl). The azygos vein represents a common venous trunk for the veins of the thoracic (10-11 right and left intercostal veins)

AZOV

and the postero-abdominal walls (lumbar veins). Phylogenetically, it is a derivative of the right cardinal vein. Its upper part lies in the lateral section of the so-called posterior mediastinum, to the right of the thoracic duct; upon reaching the third thoracic vertebra, the azygos vein arches over the right bronchus anterior to it and opens into the posterior wall of the superior vena cava. Its lower section, which pierces the diaphragm between its inner and middle crura along with the greater splanchnic nerve, is located on the right side of the vertebral column and is formed by the lumbar veins in the retroperitoneal space. In addition to the aforementioned veins, the azygos vein receives, at various levels (most frequently at the height of the eighth to ninth thoracic vertebrae), the hemiazygos vein and smaller veins of the esophagus, trachea, and posterior mediastinum. Through the spinal branches of the intercostal and lumbar veins, the system of the azygos vein communicates with the venous plexus of the vertebral column. The left renal vein also frequently gives off a root for the hemiazygos vein (anastomosis of the azygos vein). Anomalies in the position and branches of the azygos vein are quite frequent. Due to the presence of a significant number of anastomoses between the azygos vein and the inferior vena cava, replacement of the latter is possible upon its obliteration or compression, and ligation of the azygos vein is also possible.