Lumbar veins
The lumbar veins are four pairs of veins running along the inside of the posterior abdominal wall, and drain venous blood from parts of the abdominal wall. Each lumbar vein accompanies a single lumbar artery. The lower two pairs of lumbar veins all drain directly into the inferior vena cava, whereas the fate of the upper two pairs is more variable. Lumbar veins are the lumbar equivalent of the posterior intercostal veins of the thorax. Structure A lumbar vein accompanies each of the four lumbar arteries on each side of the body. Distribution and tributaries Collectively, the lumbar veins drain blood from the territories supplied by the corresponding lumbar arteries (the posterior, lateral, and anterior abdominal wall). The lumbar veins drain the anterior spinal veins. Fate The 3rd and 4th lumbar veins drain into the inferior vena cava. The fate of the two superior lumbar veins is far more variable, and may drain into either the inferior vena cava, ascending lumbar vein, azygos vein, or (on the left side) the left renal vein; the 1st lumbar vein often passes inferiorly to join the 2nd lumbar vein, but may less commonly drain into the ascending lumbar vein, or the azygos vein;