In a patient with a tumor in superior mediastinum compressing the superior vena cava, all of the following veins would serve as alternate pathways for the blood to return to the right atrium, EXCEPT:
In obstruction of the superior or inferior venae cavae, the azygos veins provide an alternative pathway for the return of venous blood to the right atrium of the hea. The azygos veins consist of the main azygos vein, the inferior hemiazygos vein, and the superior hemiazygos vein. They drain blood from the posterior pas of the intercostal spaces, the posterior abdominal wall, the pericardium, the diaphragm, the bronchi, and the esophagus. Azygos vein is often formed by the union of the right ascending lumbar vein and the right subcostal vein. It ascends through the aoic opening in the diaphragm on the right side of the aoa to the level of the fifth thoracic veebra. Here it arches forward above the root of the right lung to empty into the posterior surface of the superior vena cava. The azygos vein has numerous tributaries, including the eight lower right intercostal veins, the right superior intercostal vein, the superior and inferior hemiazygos veins, and numerous mediastinal veins. The inferior hemiazygos vein is often formed by the union of the left ascending lumbar vein and the left subcostal vein. It receives as tributaries some lower left intercostal veins and mediastinal veins. The superior hemiazygos vein is formed by the union of the fouh to the eighth intercostal veins. The internal thoracic vein drains into the brachiocephalic vein on each side. Ref: Snell's Clinical Anatomy By Regions, 8th Edition, Pages 63, 123, 866
Azygous vein
Hemiazygos vein
Internal thoracic vein
Veebral venous plexus