: In rare cases (1–2%), it may drain directly into the left brachiocephalic vein .
The accessory hemiazygos vein is an unpaired vessel that typically resides on the left side of the vertebral column, parallel to the descending thoracic aorta. accessory hemiazygos vein
: It may join the hemiazygos vein to form a common trunk before entering the azygos vein. : In rare cases (1–2%), it may drain
: It is formed by the confluence of the 4th through 8th left posterior intercostal veins . : In rare cases (1–2%)