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<\/a>Description<\/h4>\n<\/span>\n\n\nThe azygos-hemiazygos system (from Greek, azygos meaning unpaired) is a venous network found in the posterior mediastinum on each side of the vertebral column.<\/p>\n\n\n\n
\n- It begins in the thorax\u00a0at the level of the 12th thoracic vertebra,\u00a0as a collection of several veins, passing through the\u00a0aortic opening under the right crus of the diaphragm.<\/li>\n\n\n\n
- The azygos part of the system is located on the right side, while the hemiazygos system is located on the left<\/li>\n\n\n\n
- In general, the azygos-hemiazygos system\u00a0usually drains the following veins:
- Veins arising from the posterior aspect of the inferior vena cava<\/li><\/ul>\n
\n- Renal veins<\/li>\n\n\n\n
- Posterior intercostal veins<\/li>\n\n\n\n
- Bronchial veins<\/li>\n\n\n\n
- Esophageal veins<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n<\/span>\n
The azygos vein<\/h4>\n<\/span>\n\n\nThe azygos vein is formed by the right ascending lumbar vein, the right subcostal veins, and a branch from the inferior vena cava.<\/p>\n\n\n\n
\n- Connects both the superior vena cava and the inferior vena cava by forming an alternative parallel pathway to the later one<\/li>\n\n\n\n
- Drains the blood from the posterior walls of the thorax and abdomen<\/li>\n\n\n\n
- It ascends within the posterior mediastinum, as we mentioned above<\/li>\n\n\n\n
- Located at the\u00a0right side of the<\/strong>\u00a0inferior 8 thoracic vertebrae<\/strong><\/li>\n\n\n\n
- Above the root of the right lung, it\u00a0joins the superior vena cava approximately at the level of the 3rd rib<\/li>\n\n\n\n
- The\u00a0azygos vein<\/strong>\u00a0communicates with\u00a0several veins:\n
\n- Posterior intercostal veins<\/strong>\u2013 drains the back<\/li>\n\n\n\n
- Vertebral venous plexuses<\/strong>\u00a0that\u00a0drain the vertebrae.<\/li>\n\n\n\n
- Mediastinal veins<\/strong><\/li>\n\n\n\n
- Esophageal veins<\/strong><\/li>\n\n\n\n
- Bronchial veins<\/strong><\/li>\n<\/ol>\n<\/li>\n<\/ul>\n\n\n<\/span>\n
The hemizygous vein<\/h4>\n<\/span>\n\n\nArises from the Left ascending lumbar vein,<\/strong> the l<\/strong>eft subcostal, <\/strong>and often the left renal vein.<\/strong><\/p>\n\n\n\n\n- It ascends on the\u00a0left side of the vertebral column,<\/strong>\u00a0posterior to the thoracic aorta<\/strong><\/li>\n\n\n\n
- At the level of T9\u00a0vertebra<\/strong>, the hemizygous\u00a0crosses to the right, behind the aorta, the thoracic duct, and the esophagus, to finally joins the azygos vein<\/li>\n\n\n\n
- There are several veins which communicate with the hemizygous:\n
\n- Several small mediastinal veins<\/strong><\/li>\n\n\n\n
- T<\/strong>he inferior three posterior intercostal veins<\/strong><\/li>\n\n\n\n
- The inferior esophageal veins<\/strong><\/li>\n<\/ol>\n<\/li>\n<\/ul>\n\n\n<\/span>\n
The accessory hemiazygos vein<\/h4>\n<\/span>\n\n\n\n- Originates at the medial side of the\u00a04th or 5th intercostal space<\/strong>\u00a0and runs inferiorly at the left side of the vertebral column\u00a0from T5 through T8<\/strong><\/li>\n\n\n\n
- At the level of T8, the accessory hemizygous crosses to the right, behind the\u00a0thoracic aorta and the thoracic duct, to\u00a0join the azygos vein similar to the hemizygous vein<\/li>\n\n\n\n
- In some cases, the\u00a0accessory hemiazygos vein joins the hemiazygos vein<\/strong>\u00a0and opens with it into the azygos vein (referred to as indirect drainage)<\/li>\n\n\n\n
- The\u00a0accessory hemiazygos vein communicates<\/strong>\u00a0with the following veins:\n
\n- Veins in the 4th\u20138th intercostal spaces<\/strong><\/li>\n\n\n\n
- Left bronchial<\/strong>\u00a0veins<\/strong><\/li>\n\n\n\n
- Superior intercostal vein \u2013<\/strong>\u00a0drains the 1st\u20133rd intercostal spaces (although it drains into the left brachiocephalic vein.)<\/li>\n<\/ol>\n<\/li>\n<\/ul>\n<\/span>
- Veins arising from the posterior aspect of the inferior vena cava<\/li><\/ul>\n
- \n
- Renal veins<\/li>\n\n\n\n
- Posterior intercostal veins<\/li>\n\n\n\n
- Bronchial veins<\/li>\n\n\n\n
- Esophageal veins<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n<\/span>\n
The azygos vein<\/h4>\n<\/span>\n\n\n
The azygos vein is formed by the right ascending lumbar vein, the right subcostal veins, and a branch from the inferior vena cava.<\/p>\n\n\n\n
- \n
- Connects both the superior vena cava and the inferior vena cava by forming an alternative parallel pathway to the later one<\/li>\n\n\n\n
- Drains the blood from the posterior walls of the thorax and abdomen<\/li>\n\n\n\n
- It ascends within the posterior mediastinum, as we mentioned above<\/li>\n\n\n\n
- Located at the\u00a0right side of the<\/strong>\u00a0inferior 8 thoracic vertebrae<\/strong><\/li>\n\n\n\n
- Above the root of the right lung, it\u00a0joins the superior vena cava approximately at the level of the 3rd rib<\/li>\n\n\n\n
- The\u00a0azygos vein<\/strong>\u00a0communicates with\u00a0several veins:\n
- \n
- Posterior intercostal veins<\/strong>\u2013 drains the back<\/li>\n\n\n\n
- Vertebral venous plexuses<\/strong>\u00a0that\u00a0drain the vertebrae.<\/li>\n\n\n\n
- Mediastinal veins<\/strong><\/li>\n\n\n\n
- Esophageal veins<\/strong><\/li>\n\n\n\n
- Bronchial veins<\/strong><\/li>\n<\/ol>\n<\/li>\n<\/ul>\n\n\n<\/span>\n
The hemizygous vein<\/h4>\n<\/span>\n\n\n
Arises from the Left ascending lumbar vein,<\/strong> the l<\/strong>eft subcostal, <\/strong>and often the left renal vein.<\/strong><\/p>\n\n\n\n
- \n
- It ascends on the\u00a0left side of the vertebral column,<\/strong>\u00a0posterior to the thoracic aorta<\/strong><\/li>\n\n\n\n
- At the level of T9\u00a0vertebra<\/strong>, the hemizygous\u00a0crosses to the right, behind the aorta, the thoracic duct, and the esophagus, to finally joins the azygos vein<\/li>\n\n\n\n
- There are several veins which communicate with the hemizygous:\n
- \n
- Several small mediastinal veins<\/strong><\/li>\n\n\n\n
- T<\/strong>he inferior three posterior intercostal veins<\/strong><\/li>\n\n\n\n
- The inferior esophageal veins<\/strong><\/li>\n<\/ol>\n<\/li>\n<\/ul>\n\n\n<\/span>\n
The accessory hemiazygos vein<\/h4>\n<\/span>\n\n\n
- \n
- Originates at the medial side of the\u00a04th or 5th intercostal space<\/strong>\u00a0and runs inferiorly at the left side of the vertebral column\u00a0from T5 through T8<\/strong><\/li>\n\n\n\n
- At the level of T8, the accessory hemizygous crosses to the right, behind the\u00a0thoracic aorta and the thoracic duct, to\u00a0join the azygos vein similar to the hemizygous vein<\/li>\n\n\n\n
- In some cases, the\u00a0accessory hemiazygos vein joins the hemiazygos vein<\/strong>\u00a0and opens with it into the azygos vein (referred to as indirect drainage)<\/li>\n\n\n\n
- The\u00a0accessory hemiazygos vein communicates<\/strong>\u00a0with the following veins:\n
- \n
- Veins in the 4th\u20138th intercostal spaces<\/strong><\/li>\n\n\n\n
- Left bronchial<\/strong>\u00a0veins<\/strong><\/li>\n\n\n\n
- Superior intercostal vein \u2013<\/strong>\u00a0drains the 1st\u20133rd intercostal spaces (although it drains into the left brachiocephalic vein.)<\/li>\n<\/ol>\n<\/li>\n<\/ul>\n<\/span>
- Left bronchial<\/strong>\u00a0veins<\/strong><\/li>\n\n\n\n
- T<\/strong>he inferior three posterior intercostal veins<\/strong><\/li>\n\n\n\n
- At the level of T9\u00a0vertebra<\/strong>, the hemizygous\u00a0crosses to the right, behind the aorta, the thoracic duct, and the esophagus, to finally joins the azygos vein<\/li>\n\n\n\n
- Vertebral venous plexuses<\/strong>\u00a0that\u00a0drain the vertebrae.<\/li>\n\n\n\n