A 37-year-old man is brought to the emergency depament complaining of severe chest pain. His angiogram reveals thromboses of both brachiocephalic veins just before entering the superior vena cava. This condition would most likely cause a dilation of which of the following veins?

The left superior intercostal vein is formed by the second, third, and fouh posterior intercostal veins and drains into the left brachiocephalic vein, so its thrombosis leads to dilatation of left superior intercostal vein. The right superior intercostal vein drains into the azygos vein, which in turn drains into the SVC. The hemiazygos vein drains into the azygos vein, whereas the internal thoracic vein empties into the brachiocephalic vein.