Characterization of spinal tissue in lumbar spinal stenosis by advanced image analysis of MR images

Abstract

Background. Lumbar spinal stenosis (LSS) is known for causing back and leg pain due to nerve compression but the impact on structures such as intervertebral discs (IVDs), vertebrae, and ligaments is still poorly understood. This knowledge gap may limit the diagnostics and the optimization of the treatment plans for patients with LSS. The aim of the present study was to investigate whether patients with LSS exhibit tissue changes at index levels and at lumbar levels designated for surgery. Method. In 350 LSS-patients awaiting surgery, the IVDs (L1/L2 – L5/S1) and vertebrae (L1 – S1) in both T1- and T2-weighted MR images were segmented. Mean signal intensities (SIs) and standard deviations (SDs) of the means were determined globally and regionally within the segmented IVDs and globally within the vertebrae. Additionally, Δμ (a metric of disc degeneration) was determined and the entropy of the vertebral SI was introduced as a novel metric to evaluate disorganization. All metrics were analyzed for index level and levels planned for surgery and compared between groups. Additionally, Δμ and entropy were correlated to age. Results. Statistical differences in the metrics mean SI and SD were observed between index and non-index levels, as well as between segments planned and not planned for surgery. The largest differences were found in the nucleus pulposus, located in the central regions of the IVD and including subregion 2,3 and 4 (p <0.04). For vertebrae statistical differences were observed in SD and entropy for both index- and surgery level. Vertebral entropy demonstrated the strongest correlation with index levels (r = -0.166; p= 0.002). While Δμ did not display a statistical difference at a specific index level, it displayed an age dependence (e.g., IVD L1/L2; r = 0.399, p <0.001) at most lumbar levels, except at L4/L5 (r = -0.0975, p= 0.070). Δμ did also depend on specific lumbar level. In contrast, vertebral entropy displayed an age dependence at all levels, but no level-specific variation. Conclusions. This explorative study shows distinct differences in tissue characteristics in patients with LSS that correlate with index level and levels planned for surgery. As expected, Δμ was found to depend on both age and spine level. In IVDs at level L4/L5, however, an age-dependency could not statistically be established. Notably, vertebral tissue seemed to display a more homogenous pattern with age, as determined by a decreased entropy. This may reflect the transition in the bone marrow composition in older individuals. Further research is needed to explore the combined impact of multiple metrics and develop predictive tools for earlier intervention and improved clinical decision-making.