The accessory hemiazygos vein is located in the posterior mediastinum, to the left side of the bodies of the fifth, sixth, and seventh thoracic vertebrae. Above, it communicates with the lower left superior intercostal vein and below very frequently with the hemiazygos vein or with the azygos vein after crossing to the right side at the sixth or seventh thoracic vertebra. This vein varies considerably in size and arrangement, and may be absent. In the latter event, the left intercostal veins intervening between the lower left superior intercostal vein and the hemiazygos vein cross anterior to the spinal column to empty into the azygos vein. This vein crosses some of the left intercostal arteries and is covered by pleura. The fifth, sixth, and seventh left intercostal veins, the left bronchial vein, and the lower left superior intercostal vein usually empty into it. It frequently communicates by its lower end with the hemiazygos vein or with the azygos vein by crossing anterior to the spinal column.

Vena hemiazygos accessoria

Veine hémi-azygos accessoire