The hemiazygos vein (vena azygos minor inferior) is a vein running superiorly in the lower thoracic region, just to the left side of the

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordate ...

Structure

The hemiazygos vein and the

accessory hemiazygos vein The accessory hemiazygos vein, also called the superior hemiazygous vein, is a vein on the left side of the vertebral column that generally drains the fourth through eighth intercostal spaces on the left side of the body. Structure The accessor ...

, when taken together, essentially serve as the left-sided equivalent of the

azygos vein The azygos vein is a vein running up the right side of the thoracic vertebral column draining itself towards the superior vena cava. It connects the systems of superior vena cava and inferior vena cava and can provide an alternative path for blo ...

. That is, the azygos vein serves to drain most of the

posterior intercostal veins The posterior intercostal veins are veins that drain the intercostal spaces posteriorly. They run with their corresponding posterior intercostal artery on the underside of the rib, the vein superior to the artery. Each vein also gives off a dorsa ...

on the right side of the body, and the hemiazygos vein and the accessory hemiazygos vein drain most of the posterior intercostal veins on the left side of the body. Specifically, the hemiazygos vein mirrors the bottom part of the azygos vein. The structure of the hemiazygos vein is often variable. It usually begins in the left

ascending lumbar vein The ascending lumbar vein is a vein that runs up through the lumbar region on the side of the vertebral column. Structure The ascending lumbar vein is a paired structure (i.e. one each for the right and left sides of the body). It starts at the c ...

renal vein The renal veins are large-calibre veins that drain blood filtered by the kidneys into the inferior vena cava. There is one renal vein draining each kidney. Because the inferior vena cava is on the right half of the body, the left renal vein is lo ...

, and passes upward through the left crus of the diaphragm to enter the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the c ...

. It continues ascending on the left side of the

, and around the level of the ninth

thoracic vertebra In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...

, it passes rightward across the column, behind the

aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes o ...

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...

, and

thoracic duct In human anatomy, the thoracic duct is the larger of the two lymph ducts of the lymphatic system. It is also known as the ''left lymphatic duct'', ''alimentary duct'', ''chyliferous duct'', and ''Van Hoorne's canal''. The other duct is the rig ...

, to end in the

. It receives the 9th, 10th, and 11th

and the

subcostal vein The subcostal vein is a vein in the human body that runs along the bottom of the twelfth rib. It has the same essential qualities as the posterior intercostal veins The posterior intercostal veins are veins that drain the intercostal spaces post ...

of the left side, and some esophageal and mediastinal veins.

Variations

The hemiazygos may or may not be continuous superiorly with the

Clinical significance

The dilated hemiazygos system displayed by chest or abdominal X-ray films can be misdiagnosed as a mediastinal or retroperitoneal neoplasm, lymphadenopathy or aortic dissection (2, 5–7, 10). Venostasis which is the consequence of pathological conditions such as acquired obstruction of the IVC or SVC, the right heart failure, portal hypertension or due to pregnancy can have the same clinical presentation as hemiazygos continuation of the IVC (5, 6, 10, 13). In the case of hemiazygos continuation of the IVC, the hepatic veins can drain directly into the right atrium (3, 10). An incidental finding of this condition during venous cannulation for cardiopulmonary bypass complicates the procedure, since no solid IVC trunk for placing the cannula is present. Separate cannulation of the SVC and the right atrium should be used in this case.

History

The name for this vein is derived from that of the

. ''Azygos'' means 'unpaired', and ''hemi'' means half. This vein mirrors the bottom half of the azygos vein.

References

External links

* () * - "Mediastinum: The Azygos Vein and Posterior Intercostal Veins" * {{Portal bar, Anatomy Veins of the torso