Anatomical and radiological evidence for the iliolumbar vein as an inferior lumbar venous system

The purpose of this work was to study an inferior lumbar venous system, which turned out to be the vertical component of the iliolumbar vein as defined in early works by Bourgery and Jacob, though there is a terminological ambiguity between the iliolumbar vein and the ascending lumbar vein in the literature. However, the iliolumbar vein is most commonly defined as a vein draining the fourth and fifth lumbar vertebral segments. Cadaver studies, including one injection-corrosion, and in vivo venograms were analyzed by visual inspection and measurements. Whether the injection was made via the axillary or the saphenous veins, the inferior lumbar vein was always filled, demonstrating that it is part of the vertebral venous system. An interruption or a plexiform shape of the venous system at the level of the third lumbar vertebra, and an increase in caliber as this vein runs downwards, allowed differentiating the inferior lumbar vein from the ascending lumbar vein. The inferior lumbar vein and the superior iliac vein drained into the iliac veins, either external or internal iliac vein, but typically into the common iliac vein, separately or with a single common trunk. This common trunk was observed in 92% of the dissected cases on the right side and in 46% on the left, whereas it was seen in 50% of the radiological studies on the right side and 52% on the left. Consequently, the inferior lumbar vein was the main component of the iliolumbar vein, and as such should be differentiated from the ascending lumbar vein.