Magnetic resonance anatomic study of iliocava junction and left iliac vein positions related to L5-S1 disc

Study Design. An in vivo anatomic study analyzing the venous anatomy in the lumbosacral area was performed. Objectives. To obtain in vivo data concerning iliocava junction and left common iliac vein positions at L5-S1. Summary of Background Data. The left common iliac vein and the iliocava junction are at risk during L5-S1 anterior lumbar interbody fusion. Anatomic studies have demonstrated great interindividual variability in this vascular anatomy. Methods. Magnetic resonance angiography was used to study 134 patients. Image processing was carried out with maximum intensity projection algorithm and the maximum intensity projection and addition algorithm. Iliocava junction position was measured in the maximum intensity projection and addition image. Four groups of junction position were established: very high, high, low, and very low. The left common iliac vein position was measured in axial magnetic resonance images, and three groups were established: lateral, intermediate, and medial. To describe the operative window delimited by the venous structures at L5-S1, the study population was classified into 12 configurations by combining junction position and vein position values. Results. Very high lateral included 3.76% of the patients, high lateral 48.12%, high intermediate 10.53%, high medial 0.75%, low lateral 15.04%, low intermediate 4.51%, low medial 6.77%, very low lateral 0.75%, very low intermediate 2.26%, and very low medial 7.52%. Medial vein position was significantly more frequent in men. Conclusions. In 18.05% of the study population, the venous structures overlapped the center of the L5-S1 disc, reducing the operative window.