Left superior intercostal vein drains into ?

Explanation

2,3,4-posterior intercostal vein on left side drains into left superior intercostal which fuher drains into left brachiochephalic vein . Right and left brachiocephalic veins joins to form superior vena cava that opens into right atrium Posterior Intercostal Veins and their drainage: Right side drains into 1stposterior intercostal vein Right brachiocephalic vein 2,3,4 posterior intercostal vein Arch of azygos vein 5 to 11 posterior intercostal vein Azygos vein Left side drains into 1stposterior intercostal vein Left brachiocephalic vein 2,3,4-posterior intercostal vein Left brachiocephalic vein 5,6,7 posterior intercostal vein Superior hemiazygous vein 8,9,10 posterior intercostal vein Inferior hemiazygous vein