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

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.

MATERIALS AND METHODS: Consecutive patients with scoliosis and MR imaging were selected. The MR images were evaluated for tonsillar herniation and syringomyelia. On a midline T2-weighted MR image, the anteroposterior diameter of the spinal canal was measured at each cervical level, and a linear trend line was fit by least-squares regression. The slope of this line was recorded as the taper ratio in millimeters/level. Patients with >5 mm of tonsillar herniation (with or without syrinx) were compared with those without tonsillar herniation (with or without syrinx). Differences in taper ratios for the 2 groups were tested for significance by the Kruskal-Willis test with significance set at .05.

RESULTS: Fifty-four patients with scoliosis were identified; 22 had a Chiari malformation and 32 did not. Syringomyelia was identified in 20 of the patients with Chiari and in 8 of the others. The taper ratios averaged −0.9 mm/level for the patients with a Chiari malformation (with or without a syrinx) and −0.4 mm/level for those without it, significant at P = .035. Syringomyelia did not substantially alter the taper ratio in either group.

CONCLUSIONS: Patients with scoliosis with a Chiari malformation have more steeply tapering cervical spinal canals than those without it.