Purpose: To investigate the difference of intra-dural space for spinal cord in magnetic resonance imaging between patients with and without developmental cervical stenosis and its clinical significance.
Methods: 445 patients with cervical spondylotic myelopathy who had decompression surgeries were recruited. Based on their lateral radiographs, they were divided into stenosis and non-stenosis groups. On the magnetic resonance images, the ratio of the sagittal diameter of the dural sac to that of the vertebral body was measured and calculated as MRI Pavlov ratio at mid-vertebral level on sagittal images, and the ratio of the transverse area of the spinal cord to that of the dural sac was measured and calculated as occupation ratio on axial images from C3 to C7. The two ratios were compared between the two groups. We examined the correlations of the Pavlov ratio and the MRI Pavlov ratio between different vertebral levels. The correlation between the Pavlov ratio of each level and its corresponding MRI Pavlov ratio was also examined. The stenosis group was further divided into space-reserving and non-space-reserving subgroups based on their occupation ratios; then, clinical parameters were compared between the two subgroups to determine the clinical significance of the reserving space.
Results: The MRI Pavlov ratio of the stenosis group was significantly smaller at C3-C7 (P < 0.001), while the occupation ratio was larger without significance. The Pavlov and MRI Pavlov ratios were correlated significantly at different levels (P < 0.001). The Pavlov ratio correlated significantly with its corresponding MRI Pavlov ratio at each level (P < 0.001). For space-reserving subgroup, the recovery rate was lower (P < 0.05) than that for non-space-reserving group, and was higher in anterior approach than that in posterior approach (P < 0.05).
Conclusions: Developmental cervical stenosis is associated with a smaller sagittal diameter of dural sac, but does not lead to a significant decrease of intra-dural space available for the cord. For patients with normal intra-dural space, the recovery after anterior decompression surgery was better.