Comparison of the scoliosis curve patterns and MRI syrinx cord characteristics of idiopathic syringomyelia versus Chiari I malformation.

PURPOSE: Although the more readily available MR imaging has brought about more incidental findings of idiopathic syringomyelia (IS), no published study has specifically addressed the clinical and imaging features of IS-associated scoliosis. Since IS and Chiari I malformation (CMI)-type syringomyelia are hypothesized to share a common underlying developmental pathomechanism, this study aimed to investigate the scoliosis curve patterns and MRI syrinx cord characteristics of patients with IS comparing with those seen in CMI.

METHODS: Sixty-one patients with scoliosis secondary to IS were identified and reviewed retrospectively. The curve pattern and specific curve features were recorded and compared with historic CMI controls. Location, size, and morphological appearance of the syrinx were systematically assessed on MR images.

RESULTS: The maximal syrinx/cord ratio and rostrocaudal length of the syrinx in IS averaged 0.43 ± 0.16 (range 0.17-0.78) and 4.6 ± 2.5 (range 2-15) vertebral levels, respectively, both of which were smaller than those reported in CMI-type syringomyelia. Regarding the characteristics of IS-related scoliosis, sagittal profiles as well as the frequency of curve patterns and atypical features were all found to resemble those in patients with CMI (P > .05). Among the 47 individuals with a single thoracic curve, Fisher exact test revealed a significant correlation between curve convexity and the dominant side of deviated syrinx (83.3 % concordance rate, P = .021). In addition, apex of the thoracic curve trended toward being significantly correlated with the level of maximum expansion of the syrinx (P = .066).

CONCLUSIONS: Radiological characteristics of scoliosis were found to be similar between idiopathic and CMI-type syrinx in both the coronal and sagittal planes, adding further evidence to the concept that these entities may be part of a spectrum of disease sharing a common pathophysiological mechanism. The thoracic spine in IS patients tended to be convex to the deviated side of syrinx, which indirectly supported the likely role of spinal cord dysfunction in the pathogenesis of syrinx-associated spinal deformities.