Anatomical features of the cervical spinal canal in Chiari I deformity with presyrinx: A case-control study

Spinal subarachnoid space tapering in patients with syringomyelia

BACKGROUND AND PURPOSE

Cervical spine tapering affects cerebrospinal fluid dynamics. Cervical spine taper ratios derived from anteroposterior diameters reportedly differ between patients with syringomyelia and controls. We attempted to verify the differences in diameter and to show differences in cross-sectional area between syringomyelia and controls.

METHODS

Cervical spine magnetic resonance images in syringomyelia patients (idiopathic or Chiari I related) and control patients were examined. In each subject, the anteroposterior diameter of the spinal canal was measured at each cervical level, and C1-C4, C4-C7, and C1-C7 taper ratios were calculated. Differences in taper ratio between groups were tested for statistical significance with the t-test. Cross-sectional areas of the spinal canal were measured at each cervical spinal level, and tapering was calculated.

RESULTS

Eighteen patients with idiopathic syringomyelia, 28 with Chiari I, and 29 controls were studied. Chiari and syringomyelia patients had significantly steeper diameter-based taper ratios than controls. The dural sac areas tapered proportionally with the diameter-based taper ratio in all groups.

CONCLUSIONS

Cervical spine anteroposterior diameter tapering and dural sac cross-sectional areas tapering differ between syringomyelia patients and controls.

Cervical spine taper ratios: Normal tolerance limits

Background Spinal canal tapering, which can be measured as taper ratios, affects cerebrospinal fluid flow dynamics. We calculated the tolerance interval for normal cervical spine taper ratios to facilitate the detection of abnormal taper ratios. Methods We collected a series of patients who had cervical spine magnetic resonance studies reported as normal. We measured anteroposterior diameters of the cervical spine and calculated C1-C4, C4-C7, and C1-C7 taper by standard methodology. We calculated the normal tolerance limits for taper ratios and compared results of this study with data in previous reports on taper ratios. Results We enrolled 78 patients aged 2-55 years. The 99% tolerance limits for the taper ratios for C1-C4, C4-C7, and C1-C7 were -0.31 to +0.09, -0.11 to +0.14, and -0.13 to +0.05 cm/level, respectively. Age and sex were not significant variables for taper ratios. Taper ratios in this study agreed with those reported for controls in previous studies. Patients with syringomyelia in previous reports tended to have taper ratios outside the normal tolerance limits. Conclusion Normal limits of the cervical taper ratios are reported.