Vena Azygos - Vena Azigos by A.Griguolo

Generality

The azygos vein is an uneven vein of the human body, which flows mainly into the thoracic cavity and flows into the superior vena cava.

The azygos vein begins its course just below the diaphragm, at the same height as the T12 thoracic vertebra; from here, take the aortic hiatus and begin to ascend the thorax to the right of the vertebral column up to the thoracic vertebra T4, point where it bends and joins - as anticipated - to the superior vena cava.

Equipped with numerous tributary veins, the azygos vein has the task of draining deoxygenated blood coming from the back of the thorax and from the upper portion of the abdomen, and discharging it into the superior vena cava (which, then, will "pour" it into the right atrium of the heart).

Short review of what a vein is

In human anatomy, the list of veins includes any blood vessel responsible for transporting blood from the periphery (where the body's tissues and organs are meant for the periphery) to the heart.

Contrary to what many people think, in the veins NOT only non-oxygenated blood flows (ie oxygen-free); to demonstrate what is just stated is the existence of pulmonary veins, ie the venous vessels designed to carry oxygen-rich blood from the lungs to the heart, so that the latter can then spread it to the periphery.

The veins differ from the arteries from the structural point of view: compared to the second, the former are less extensible and less thick.

What is the Vena Azygos?

The vein azygos is an uneven vein of the human body, situated at the level of the trunk, which rises, to the right of the spine, the abdomen, first, and the thorax, then, and concludes its own path leading to the superior vena cava .

The azygos vein is part of the so-called azygos venous system, which is the vein complex that includes, in addition to the azygos vein in question, the vein emiazygos and the accessory hemiazygos vein .

Azygos venous system: what is it for?

The azygos venous system has the task of draining the oxygen-free blood from the posterior thoracic wall and the upper lumbar region (through the lumbar veins and the posterior intercostal veins).

Furthermore, in the case of obstruction at the level of the hollow veins, it is assumed that the latter is replaced to restore blood to the right atrium of the heart.

Anatomy

Premise: in anatomy, the description of the course of veins and arteries along the human body is based on the direction of blood flow; in practical terms, this means that the description of the path of a vein will start from the periphery (venous blood runs from the periphery to the heart), while the description of the path of an artery will start from the end closest to the heart (arterial blood flows from the heart to the periphery).

The azygos vein begins in the abdomen, just below the diaphragm, and continues into the thorax, until it joins the superior vena cava.

Long from the thoracic vertebra T12 to the thoracic vertebra T4, the azygos vein is the protagonist of a path of ascent with cranial direction, which leads it to be placed to the right and slightly ahead of the vertebral column, and posteriorly to the system of the caves veins.

During its ascent towards the superior vena cava, the azygos vein receives several smaller or at least less important veins; these are the so-called tributaries of the azygos vein .

Origin of the azygos vein: the details

Taken from Wikipedia.org

The azygos vein originates from the union of the right ascending lumbar vein with the right subcostal vein, a union that generally takes place at the height of the thoracic vertebra T12 and of the renal veins.

The T12 thoracic vertebra is the last vertebra of the thoracic tract of the spine; after it, in fact, the lumbar spine begins.

The starting point of the azygos vein is slightly below the diaphragm, in an anatomical section of the trunk that is more correct to consider abdomen.

Path of the Vena Azygos: the details

The azygos vein stops very little in the abdomen; immediately after its origin, in fact, it passes into the thoracic cavity through the posterior opening to the diaphragm called aortic hiatus (or aortic or aortic foramen opening ).

Resulting from the particular arrangement of the diaphragm with respect to the vertebral column, the aortic hiatus is delimited by the median arcuate ligament, anteriorly, from the right and left pillars of the diaphragm (the so-called crus of the diaphragm ), laterally, and from the inferior margin of the body of the XII thoracic vertebra, later.

In addition to the azygos vein, the aortic hiatus also guarantees the passage to the abdominal aorta and the thoracic duct (structure of the lymphatic system).

With the crossing of the diaphragm, the azygos vein flows into the mediastinum - to be precise in the posterior mediastinum - and here begins the aforementioned ascent of the thorax to the right of the spine.

The path of ascent of the azygos vein is linear up to the thoracic vertebrae T5 and T6, where the vein in question forms an arch - called the arch of the azygos vein - essential for being able to "embrace" the path of the superior vena cava.

Equipped with a particular valve, the arch of the azygos vein takes shape at the level of the right main bronchus, posterior to the root of the right lung .

The arch of the azygos vein is an important anatomical reference point in the description of the vein in question.

Placed at the same height as the T4 thoracic vertebra, the junction with the superior vena cava, by the azygos vein, represents the conclusion of the latter.

Tributaries of the Vena Azygos

Premise: in anatomy, the veins that converge in another venous vessel, generally more important, draining the proper content of deoxygenated blood, are called tributary veins.

The most tributary veins of the azygos vein are:

The vein emiazygos. Located to the left of the vertebral column, this venous vessel originates from the left ascending lumbar vein (more or less at the same level as where the azygos vein arises), crosses the left diaphragmatic crus and ascends the thorax to the T9 thoracic vertebra, where it performs a curve that serves for joining the vein azygos.
The emiazygos vein has the task of draining the IX, X and XI posterior intercostal vein of the left side of the human body.
In fact, on the left half of the human body, the hemiazygos vein mirrors the first part of the azygos vein;
The accessory hemiazygos vein. Located to the left of the vertebral column, this venous vessel originates from the confluence of the IV, V, VI, VII and VIII left intercostal intercostal vein, and joins the azygos vein at the level of the T8 thoracic vertebra.
In addition to draining the aforementioned left posterior intercostal veins, the accessory hemiazygos vein drains the bronchial veins and esophageal veins;
The right rear intercostal veins ;
The right upper frenic vein ;
The right upper intercostal vein ;
Tracheal veins ;
Esophageal veins ;
Bronchial veins ;
Pericardial veins .

Relationships of the Vena Azygos

The azygos vein borders:

The vertebral bodies of the T5-T12 tract, the anterior longitudinal ligament and the right posterior intercostal arteries, posteriorly;
The inferior vena cava and the superior vena cava, anteriorly;

Taken from Wikipedia.org

The big splancnic right nerve, the right pleura and the right lung, on the left side;
The thoracic duct, the aorta, the esophagus, the trachea and the right vagus nerve, on the right side.

variants

As with many other structures of the human body, anatomical variants also exist for the azygos vein, ie versions of the venous vessel in question slightly different, in terms of anatomy, from what has been reported so far.

The most important variants of the azygos vein include:

The azygos vein with a more central positioning, almost in correspondence with the median plane that divides into the body in two equal and symmetrical halves;
The azygos vein as an equal vascular element, present to the right and to the left of the vertebral column;
The azygos vein that passes through the right diaphragmatic crus (instead of the aortic hiatus);
The azygos vein with origin in the first lumbar vertebrae (L1 or L2);
The azygos vein associated with the so-called azygos lobe, an abnormal lobe of the right lung, which is combined with the 3 usually present.
The azygos vein associated with the so-called azygos lobe is the result of an error, during embryonic development, of the process that causes the posterior cardinal vein to migrate beyond the apex of the right lung.

Even if it happens very rarely, some individuals may be born without the azygos vein.

Function

Thanks also to its own tributary veins, the azygos vein has the function of draining deoxygenated blood coming from the back of the thorax and from the upper portion of the abdomen, and discharging it into the superior vena cava (which, then, will "deliver" it to the atrium right side of the heart).

Furthermore, it has the further task of taking the place of the veins in the caves, when the latter present an obstruction.

diseases

From the pathological point of view, the azygos vein can be the protagonist of lacerations and aneurysms .

Tearing of the Vena Azygos

The lacerations of the azygos vein are real lesions of the vessel in question.

Most cases of laceration of the azygos vein are caused by blunt trauma to the chest, resulting in road accidents and accidental falls from above.

With more frequent location at the level of the arch of the azygos vein, the lacerations of the azygos vein produce hemothorax, ie the abnormal accumulation of blood in the pleural space.

The treatment of lacerations of the azygos vein involves the thoracotomy aimed at draining the hemothorax.