An Anatomical Clue for Minimizing Iliac Vein Injury During the Anterolateral Approach at L5-S1 Level: A Cadaveric Study

Objective: The injury to the common iliac vein (CIV) seems to be the most important concern during the anterior approach to the spine at L5-S1 level. We investigated the anatomy of the L5-S1 vertebral structures related to the CIV through a cadaveric study to find an anatomical clue for safe dissection of CIV. Methods: Ten cadavers were prepared for this study. After removing the peritoneum and the presacral fascia, the section from the lower part of the L5 to the upper part of the S1 vertebral body was removed with the CIV attached. After decalcification, 2 sections in the vertical and horizontal directions were made for histological study. Results: An adipose tissue layer was present between the intervertebral disc and CIV. The adipose tissue layer in 6 cadavers was thin, and in 3 of these cadavers, the CIV was attached to the vertebral body and the disc. In the other 4 cadavers, the CIV was clearly separated from the vertebral body and the disc by the intervening adipose tissue layer (IATL). Under the microscope, a thin layer surrounding the anterior longitudinal ligament, periosteum, and disc was observed, and we named this structure the 'perivertebral membrane'. The perivertebral membrane was attached to the CIV when there was no IATL, but a potential space was detected under the membrane. Conclusion: There was a thin membrane, perivertebral membrane, between the CIV and L5-S1 disc. In cases with CIV adhesion to the disc due to the absence of IATL, the CIV may be mobilized indirectly through the perivertebral membrane.