Correlative study of nerve root sedimentation sign and compression of dural sac in the diagnosis of severe central/complex lumbar spinal stenosis

English Keywords:Lumbar spinal stenosis  Nerve root sedimentation sign  Cross-sectional area of dural sac  Posteroanterior diameter of the spinal canal  Cross-sectional area difference of dural sac  Correlative study

English Abstract:

  【Abstract】 Objectives: To evaluate the relationship between the presence of nerve root sedimentation sign(SedSign) on MRI and the cross-sectional area changes of dural sac in diseased levels in patients with severe lumbar spinal stenosis(LSS), and to analyze the possible mechanism of sedimentation sign. Methods: From January 2012 to June 2015, MR images of 87 patients with LSS were analyzed in the second affiliated hospital of Qiqihar Medical College, all patients were diagnosed with central/complex LSS. A cross-sectional area(CSA) of dural sac ≤80mm2 at least one level in transverse MRI scans of L3/4 or L4/5 were determined. All patients had typical intermittent claudication with walking distance ≤500m. 61 patients were diagnosed with single segment stenosis(19 patients at L3/4 level and 42 patients at L4/5 level). Two levels stenosis(L3/4, L4/5) were found in 26 patients. 113 narrowing levels were selected and the prevalence of positive sedimentation sign were recorded, and all cases were divided into positive and negative groups. Each level of L3/4 and L4/5 was scanned in three layers, and the smallest CSA of dural sac, the smallest posteroanterior diameter(PAD) of the spinal canal and the largest cross-sectional area difference(CSAD) of dural sac were measured at transverse T2-weighted MRI respectively, the difference of two groups were compared by t-test. The receiver-operator characteristic(ROC) curve analysis was conducted to evaluate the correlations between positive sign and the smallest CSA, the smallest PAD and the largest CSAD. Results: The positive sedimentation sign in 113 narrow levels accounted for 75.22%(85 levels). The smallest PAD of the positive groups was 12.00±2.10mm, and the negative was 11.47±2.04mm, there were significant differences between the two groups(P<0.05). The largest CSAD of the positive groups was 36.94±13.97mm2, and the negative was 18.60±7.70mm2, there were significant differences between the two groups(P<0.01). The smallest CSA of the positive groups was 47.34±12.55mm2, and negative was 45.16±15.35mm2, there were no significant differences between the two groups(P>0.05). The ROC curve showed that the area under ROC curve(AUC) of the smallest PAD of spinal canal was 0.64(P<0.05) and the AUC of the largest CSAD of dural sac was 0.929(P<0.01), the AUC of the smallest CSA was 0.557(P>0.05). Conclusions: In summary, the positive sedimentation sign is closely related to the change of compressed dural sac. The CSAD is proposed to describe the change of dural sac in compressive levels in severe central/complex lumbar stenosis.