The azygos system of veins consists of several longitudinal vessels on both sides of the spine that collect blood from the viscera of the mediastinum, as well as the back and thoracic and abdominal walls. These veins ascend to empty into the superior vena cava (read more!).

Also, some veins from the thoracic viscera may drain into the azygos venous system, and azygos venous system forms anastomoses with the abdominal veins. Overall, the longitudinal vessels of the azygos venous system on each side of the spine are interconnected at various points throughout their course.

The azygos venous system is an important anastomotic pathway that can return venous blood to the heart from the lower part of the body if the inferior vena cava (read more!) is blocked.

The major veins of this system are:

On the left - azygos vein (read more!);
On the right, its two tributaries - hemiazygos vein (read more!) and accessory hemiazygos vein (read more!).

The origin, course, tributaries, anastomoses and termination sites of these vessels are quite variable.

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Azygos venous system