The iliolumbar vein is one of two named tributaries of the common iliac vein (Read more!). It arises from several smaller veins - such as the iliacus vein, fourth and fifth lumbar veins, and spinal veins - which drain the iliac fossa, lumbar region, and vertebral canal. Along its course, this vein accompanies the iliolumbar artery and drains the structures supplied by it.

After its formation, the iliolumbar vein travels medially and slightly anteriorly, passing behind the psoas major muscle and heading toward the pelvic cavity. As it approaches the pelvic cavity, the iliolumbar vein crosses posterior to the external iliac vessels and runs along the medial border of the psoas major, situated between the obturator nerve and lumbosacral trunk, before draining into the common iliac vein. It is also closely related to the ascending lumbar vein.

Although the common iliac vein is its usual drainage point, the iliolumbar vein may occasionally drain into the internal iliac veins, or bifurcate and drain into both the internal iliac vein and the common iliac vein. Other variations include differences in the number and branching patterns of the veins.

Overall, the iliolumbar vein drains the structures in the iliac fossa, as well as the lumbar and sacral regions. These also include the ilium, fourth and fifth lumbar vertebrae, iliacus, psoas major, and quadratus lumborum.

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Iliolumbar vein