Azygos vein drains into:

The azygos vein ends by joining the posterior aspect of the superior vena cavaThe Azygos VeinThe azygos vein connects the superior and inferior venae cavae, either directly by joining the IVC or indirectly by the hemiazygos and accessory hemiazygos veins.The azygos vein drains blood from the posterior walls of the thorax and abdomen.It ascends in the posterior mediastinum, passing close to the right QA des of the bodies of the inferior eight thoracic veebrae (T4-T12).It is covered anteriorly by the oesophagus as it passes posterior to the root of the right lung.It then arches over the superior aspect of this root to join the SVC.In addition to the posterior intercostal veins, the azygos vein communicates with the veebral venous plexuses.This vein also receives the mediastinal, oesophageal, and bronchial veins.