Segmental Variation in Lumbar Nerve Root Weight: A Donor-Body Study

Introduction The cauda equina consists of lumbosacral nerve roots extending from the conus medullaris within the lumbar cistern. Although radiographic imaging is essential for evaluating lumbar spinal pathology, normal anatomical variation in the cauda equina may affect its appearance. This donor-body study quantified normalized segmental linear mass per root across the L1-L2 through L4-L5 vertebral intervals and evaluated level-specific and demographic patterns. These measurements provide exploratory anatomical data for future imaging and clinical correlation studies. Methods Thirty-two donor bodies underwent posterior lumbar dissection from L1 through L5. The craniocaudal length of each lumbar interval was measured using vertebral body borders as standardized anatomical endpoints. The dura and neural contents were removed en bloc, after which the dura and all visible connective tissue were removed. The isolated neural tissue was transected at the corresponding vertebral body borders, allowed to become free of visible surface moisture, and weighed in milligrams. Normalized segmental linear mass per root was calculated by dividing the segment mass by its measured length and the estimated mean number of root components traversing that interval. Results Normalized segmental linear mass per root differed significantly across lumbar levels (Friedman χ²(3) = 24.30, p = 2.16 × 10⁻⁵). The highest median value was observed at L1-L2 (1.42 × 10⁻³ mg/mm per root), and the lowest was observed at L4-L5 (0.97 × 10⁻³ mg/mm per root). After Bonferroni correction, L4-L5 values were significantly lower than those at L1-L2, L2-L3, and L3-L4. No association with age, height, body weight, or sex remained statistically significant after false discovery rate (FDR) correction. Conclusions Normalized segmental linear mass per root generally decreased caudally and was lowest at L4-L5. No demographic association remained statistically significant after correction for multiple comparisons. These findings provide exploratory anatomical data regarding level-specific variation within the cauda equina; their imaging, procedural, and clinical implications require validation through studies directly correlating anatomic measurements with imaging and clinical outcomes.