The Cervical Spinal Canal Tapers Differently in Patients with Chiari I with and without Syringomyelia.

A Thompson,A Munoz Del Rio,G Weinstein,V Haughton,J.R Hesselink,N Madan

doi:10.3174/ajnr.a4597

Abstract

The cause of syringomyelia in patients with Chiari I remains uncertain. Cervical spine anatomy modifies CSF velocities, flow patterns, and pressure gradients, which may affect the spinal cord. We tested the hypothesis that cervical spinal anatomy differs between Chiari I patients with and without syringomyelia. We identified consecutive patients with Chiari I at 3 institutions and divided them into groups with and without syringomyelia. Five readers measured anteroposterior cervical spinal diameters, tonsillar herniation, and syrinx dimensions on cervical MR images. Taper ratios for C1-C7, C1-C4, and C4-C7 spinal segments were calculated by linear least squares fitting to the appropriate spinal canal diameters. Mean taper ratios and tonsillar herniation for groups were compared and tested for statistical significance with a Kruskal-Wallis test. Inter- and intrareader agreement and correlations in the data were measured. One hundred fifty patients were included, of which 49 had syringomyelia. C1-C7 taper ratios were smaller and C4-C7 taper ratios greater for patients with syringomyelia than for those without it. C1-C4 taper ratios did not differ significantly between groups. Patients with syringomyelia had, on average, greater tonsillar herniation than those without a syrinx. However, C4-C7 taper ratios were steeper, for all degrees of tonsil herniation, in patients with syringomyelia. Differences among readers did not exceed differences among patient groups. The tapering of the lower cervical spine may contribute to the development of syringomyelia in patients with Chiari I.

Highlights

BACKGROUND AND PURPOSEThe cause of syringomyelia in patients with Chiari I remains uncertain
The tapering of the lower cervical spine may contribute to the development of syringomyelia in patients with Chiari I
Patients with a Chiari I malformation frequently develop syringomyelia, in theory the result of CSF flow obstructed by ectopic cerebellar tonsils

Summary

MATERIALS AND METHODS

Approval for this retrospective study was obtained from the respective institutional review boards of the 3 sites: the University of Wisconsin School of Medicine and Public Health, Tufts University. Inclusion criteria were any patient with sagittal T2-weighted fast spin-echo cervical spine images (at 1.5T or 3T) who had Ն5-mm cerebellar tonsil herniation. The anteroposterior diameter of the cervical spinal canal from C1 to C7 was measured on the midline sagittal T2 images by a previously described method.[6,7] At each level, a line was placed perpendicular to the spinal axis at the midpoint of the vertebra, the points where it crossed from CSF to epidural tissue were identified, and the distances between them were measured. The readers measured the maximal anteroposterior diameter of the syrinx on the midsagittal T2-weighted image. Analysis and Statistical Testing The diameter measurements for all readers were tabulated together with the patient age, sex, tonsillar herniation, syrinx location, and dimensions. We calculated the bias and the typical discrepancy between 2 measurements, accounting for the clustering that results from combining multiple diameters from the same subject.[9]

RESULTS

CONCLUSIONS