Tapering of the cervical spinal canal in patients with distended or nondistended syringes secondary to Chiari type I malformation.

BACKGROUND AND PURPOSE Steeper tapering of the cervical spinal canal as documented in recent studies is thought to have a role in the pathophysiology of Chiari malformation-associated syringomyelia. This study aimed to determine whether taper ratio of the cervical spinal canal differs between patients with distended and nondistended syringes. MATERIALS AND METHODS Seventy-seven adolescents (10-18 years) were divided into 2 groups: 44 with distended syrinx and 33 with nondistended syrinx. On T2-weighted MR images, anteroposterior diameter of the spinal canal was measured at each cervical level, and a linear trend line was fit by least squares regression to calculate the taper ratio. Taper ratios were compared between the 2 groups and further evaluated with respect to age and sex. RESULTS In the nondistended group ND, the taper ratios for C1-C7, C1-C4, and C4-C7 averaged -0.73 ± 0.57, -1.61 ± 0.98, and -0.04 ± 0.54, respectively, all of which were significantly steeper than those observed in the distended group (P = .001, .004, and .033, respectively). Regarding the average diameters plotted by cervical level, the narrowest region of the canal was found to occur at C4 in both groups. In addition, no significant differences in taper ratio were noted between males and females, or between older (>14 years) and younger patients (≤14 years). CONCLUSIONS Taper ratios of the cervical spinal canal were found to be different between patients with distended and nondistended syringes, indicating a reciprocal interaction between the syrinx and the cervical spine anatomy.