Superior vena cava system

The superior vena cava (v. cava superior) is a short valveless vessel with a diameter of 21-25 mm and a length of 5-8 cm, which is formed as a result of the confluence of the right and left brachiocephalic veins behind the junction of the cartilage of the first right rib with the sternum. This vein runs vertically downwards and at the level of the junction of the third right cartilage with the sternum it flows into the right atrium. In front of the vein are the thymus and the mediastinal part of the right lung covered with pleura. The mediastinal pleura adjoins the vein on the right, and the ascending part of the aorta on the left. With its posterior wall, the superior vena cava is in contact with the anterior surface of the root of the right lung. The azygos vein flows into the superior vena cava on the right, and the small mediastinal and pericardial veins flow into it on the left. The superior vena cava collects blood from three groups of veins: the veins of the walls of the chest and part of the abdominal cavity, the veins of the head and neck, and the veins of both upper limbs, i.e. from those areas that are supplied with blood by the branches of the arch and thoracic part of the aorta.

The azygos vein (v. azygos) is a continuation in the thoracic cavity of the right ascending lumbar vein (v. lumbalis ascendens dextra), which passes between the muscle bundles of the right crus of the lumbar part of the diaphragm into the posterior mediastinum and on its way anastomoses with the right lumbar veins flowing into the inferior vena cava. Behind and to the left of the azygos vein are the vertebral column, the thoracic aorta and thoracic duct, as well as the right posterior intercostal arteries. The esophagus lies in front of the vein. At the level of the IV-V thoracic vertebrae, the azygos vein bends around the root of the right lung from behind and above, then goes forward and downward and flows into the superior vena cava. There are two valves at the mouth of the azygos vein. On its way to the superior vena cava, the hemiazygos vein and the veins of the posterior wall of the thoracic cavity flow into the azygos vein: the right superior intercostal vein; the posterior intercostal veins, as well as the veins of the organs of the thoracic cavity: the esophageal, bronchial, pericardial and mediastinal veins.

The hemiazygos vein, sometimes called the left or lesser hemiazygos vein, is thinner than the azygos vein because it receives only 4-5 lower left posterior intercostal veins. The hemiazygos vein is a continuation of the left ascending lumbar vein (v.lumbalis ascend ens sinistra) and passes between the muscle bundles of the left crus of the diaphragm into the posterior mediastinum, adjacent to the left surface of the thoracic vertebrae. To the right of the hemiazygos vein is the thoracic aorta, and behind it are the left posterior intercostal arteries. At the level of the 7th-10th thoracic vertebrae, the hemiazygos vein turns sharply to the right, crosses the vertebral column in front, is located behind the aorta, esophagus and thoracic duct) and flows into the azygos vein. The accessory hemiazygos accessoria (v. hemiazygos accessoria), which flows from top to bottom and receives 6-7 upper intercostal veins (I-VII), as well as the esophageal and mediastinal veins, flows into the hemiazygos vein. The most significant tributaries of the azygos and hemiazygos veins are the posterior intercostal veins, each of which is connected by its anterior end to the anterior intercostal vein, a tributary of the internal thoracic vein. The presence of such venous connections creates the possibility of venous blood flowing from the walls of the chest cavity back into the azygos and hemiazygos veins and forward into the internal thoracic veins.

The posterior intercostal veins (vv. intercostales posteriores) are located in the intercostal spaces next to the arteries of the same name (in the groove of the corresponding rib). These veins collect blood from the tissues of the walls of the chest cavity and partly the anterior abdominal wall (lower posterior intercostal veins). The dorsal vein (v. dorsalis), which forms in the skin and muscles of the back, and the intervertebral vein (v. intervertebralis), which is formed from the veins of the external and internal vertebral plexuses, flow into each of the posterior intercostal veins. A spinal branch (v. spinalis) flows into each intervertebral vein, which, along with other veins (vertebral, lumbar and sacral), participates in the outflow of venous blood from the spinal cord.

The internal (anterior and posterior) vertebral venous plexuses (plexus venosi vertebrales interni, anterior et posterior) are located inside the spinal canal (between the dura mater of the spinal cord and the periosteum) and are represented by veins that anastomose with each other multiple times. The plexuses extend from the foramen magnum to the apex of the sacrum. The spinal veins and veins of the spongy substance of the vertebrae flow into the internal vertebral plexuses. From these plexuses, blood flows through the intervertebral veins, passing through the intervertebral openings (near the spinal nerves), into the azygos, hemiazygos and accessory hemiazygos veins. Blood from the internal plexuses also flows into the external (anterior and posterior) venous vertebral plexuses (plexus venosi vertebrales externi, anterior et posterior), which are located on the anterior surface of the vertebrae and also encircle their arches and processes. From the external vertebral plexuses, blood flows into the posterior intercostal, lumbar and sacral veins (vv. intercostales posteriores, lumbales et sacrales), as well as directly into the azygos, hemiazygos and accessory hemiazygos veins. At the level of the upper part of the spinal column, the veins of the plexuses flow into the vertebral and occipital veins (vv. vertebrates et occipitales).

The brachiocephalic veins (right and left) (vv. brachiocephalicae, dextra et sinistra) are valveless and are the roots of the superior vena cava. They collect blood from the organs of the head and neck and the upper limbs. Each brachiocephalic vein is formed from two veins - the subclavian and internal jugular.

The left brachiocephalic vein is formed behind the left sternoclavicular joint. The vein is 5-6 cm long, and runs obliquely downwards and to the right from the site of its formation behind the manubrium of the sternum and the thymus. Behind this vein are the brachiocephalic trunk, the left common carotid and subclavian arteries. At the level of the cartilage of the right 1st rib, the left brachiocephalic vein joins the right vein of the same name, forming the superior vena cava.

The right brachiocephalic vein, 3 cm long, forms behind the right sternoclavicular joint. The vein then descends almost vertically behind the right edge of the sternum and adjoins the dome of the right pleura.

Small veins from the internal organs flow into each arm of the cephalic vein: thymic veins (vv. thymicae); pericardial veins (vv. pericardiacae); pericardiodiaphragmatic veins (vv. pericardiacophrenicae); bronchial veins (vv. bronchiales); esophageal veins (vv. oesophageales); mediastinal veins (vv. mediastinales) - from the lymph nodes and connective tissue of the mediastinum. The larger tributaries of the brachiocephalic veins are the inferior thyroid veins (vv. thyroideae inferiores, 1-3 in total), through which blood flows from the unpaired thyroid plexus (plexus tliyroideus impar), and the inferior laryngeal vein (v. laryngea inferior), which brings blood from the larynx and anastomoses with the superior and middle thyroid veins.

The vertebral vein (v. vertebralis) passes together with the vertebral artery through the transverse openings of the cervical vertebrae to the brachiocephalic vein, receiving on its way the veins of the internal vertebral plexuses.

The deep jugular vein (v. cervicalis profunda) originates from the external vertebral plexuses, collects blood from the muscles and fasciae located in the occipital region. This vein passes behind the transverse processes of the cervical vertebrae and flows into the brachiocephalic vein near the mouth of the vertebral vein or directly into the vertebral vein.

The internal thoracic vein (v. thoracica interna) is paired and accompanies the internal thoracic artery. The roots of the internal thoracic veins are the superior epigastric vein (v. epigastrica superioris) and the muscular-diaphragmatic vein (v. musculophrenica). The superior epigastric vein anastomoses in the thickness of the anterior abdominal wall with the inferior epigastric vein, which flows into the external iliac vein. The anterior intercostal veins (vv. intercostales anteriores), located in the anterior parts of the intercostal spaces, flow into the internal thoracic vein and anastomose with the posterior intercostal veins, which flow into the azygos or hemiazygos vein.

The highest intercostal vein (v. intercostalis suprema) flows into each brachiocephalic vein, right and left, collecting blood from the 3-4 upper intercostal spaces.