Tapering of the Cervical Spinal Canal in Patients with Scoliosis with and without the Chiari I Malformation

Abstract

BACKGROUND:Cervical spinal canal tapering may increase CSF velocities and pressures. One report suggests that the cervical spinal canal tapers more steeply in patients with Chiari I than in healthy subjects. The goal of this study was to test the conclusion by measuring spinal canal tapering in another cohort of patients.

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

“…In a previous report of 2 patients with scoliosis with and 20 without syrinx, the presence of a syrinx does not produce a significant difference in the C1 to C7 taper ratios. 8 The small sample size may explain the difference from our results.…”

“…6,7 Taper ratios, the slope of a line fit to spinal canal diameters at multiple spinal levels, differ between patients with Chiari I and controls. 5,8 We designed this study to test the hypothesis that Chiari I patients with syringomyelia have different cervical spinal canal taper ratios than Chiari I patients without syringomyelia.…”

Tapering of the Cervical Spinal Canal in Patients with Distended or Nondistended Syringes Secondary to Chiari Type I Malformation

“…16, 17 Hirano et al, 16 in their retrospective review of 21 patients, noted a statistically steeper taper ratio of the upper cervical spinal canal in patients with CMI and SM. Concerning patients with CMI but no syrinx, however, taper ratio was found to be similar to that of their age-and sex-matched control subjects.…”

“…In line with the methods described previously, 16,17 the anteroposterior diameter of the cervical spinal canal was measured on T2-weighted MR images for each level at the midpoint of the vertebral body (in the case of C1, at the midportion of the anterior arch), along a line perpendicular to the spinal axis extending from the anterior to the posterior edge of the subarachnoid space (Fig 1). The diameters of the spinal canal were plotted against the cervical level.…”

“…These findings, coupled with the mesodermal dysgenesis theory as evidenced by hypoplasia of the posterior cranial fossa, 14,15 imply an abnormal cervical spinal canal anatomy in patients with CMI. In an attempt to verify this hypothesis, Hirano et al 16 and Hammersley et al 17 investigated tapering of the upper cervical spinal canal, and as steeper taper ratio was found in patients with CMI as compared with healthy controls, they speculated that such bony variations might increase the pressure gradients between the cranial and caudal ends of the spinal canal, resulting in dysfunctional CSF flow and thus favoring the formation of a syrinx. Despite the elegance of the work of Hirano et al 16 and Hammersley et al, 17 which added an interesting twist to the pathomechanism of SM, their theory fails to account for the influence of a syrinx upon morphology of the cervical spinal canal.…”