: It may join the hemiazygos vein to form a common trunk before entering the azygos vein.
: It is formed by the confluence of the 4th through 8th left posterior intercostal veins . accessory hemiazygos vein
: If the vein is underdeveloped or absent, the left superior intercostal vein may extend further down to drain those levels. Clinical Significance Accessory Hemiazygos Vein | Complete Anatomy - Elsevier : It may join the hemiazygos vein to