Radiological Features of Scoliosis in Chiari I Malformation Without Syringomyelia

Study Design. A retrospective radiographic analysis. Objective. The aim of this study was to investigate the scoliosis curve patterns/features and magnetic resonance imaging (MRI) tonsillar ectopia characteristics in Chiari I malformation without syringomyelia (CMI-only). Summary of Background Data. The development of scoliosis associated with a CMI typically has been ascribed to the presence of syringomyelia. However, a subset of CMI patients with scoliosis may not have a concomitant syrinx. Scoliosis in these patients has been very poorly documented in the literature. Methods. A retrospective study was conducted on patients with a scoliosis secondary to CMI-only. The curve direction, curve pattern/features, and side of the dominant tonsillar ectopia were recorded and assessed quantitatively. On the basis of the measurement results, associations between the scoliosis curve patterns/features and MRI tonsillar ectopia characteristics were analyzed. Results. A total of 26 patients, consisting of seven males and 19 females with an average age of 15.4 years, were included in the current study. In 19 patients with asymmetrically displaced tonsils, the concordance between the dominant side of the asymmetrically displaced tonsils and curve direction was 78.9%. A statistically significant association was found between the dominant side of the tonsillar ectopia and the convex side of scoliosis according to Fisher exact test (P = 0.045). In addition, it was noted that there was a high incidence (52.9%) of atypical curve patterns in CMI-only patients. A significantly high incidence of atypical features with a superior shift of either the apical or the end vertebrae was found in 85.7% of thoracic curves and 40% of lumbar curves. Conclusion. Scoliosis associated with CMI-only was found to have atypical curve patterns in all cases, and the direction of scoliosis was highly consistent with the dominant side of asymmetrically tonsillar herniation. These findings should be considered as an argument in favor of a nonidiopathic etiology and lead to more evidence that simple tonsillar impaction can provide enough impetus to produce or exaggerate scoliotic curvature. Level of Evidence: 3