Dynamic MRI in the Evaluation of the Cervical Spine in Pediatric Patients With Achondroplasia

The main objective of this study is to establish normative craniocervical junction parameters in pediatric patients with achondroplasia and evaluate differences between patients with and without symptoms of foramen magnum stenosis (FMS) using static and dynamic MRI. A retrospective chart review identified 80 pediatric patients with achondroplasia evaluated at a single institution between 2007 and 2023. Patients were categorized into two groups based on clinical presentation: those with symptoms suggestive of FMS (FMSS group) and those who underwent imaging for unrelated indications (Non-FMSS group). Craniocervical MRI parameters, including minimal canal and cord diameters, atlanto-dental interval (ADI), clival-axial angle (CXA), and space available for the cord (SAC), were measured in neutral, flexion, and extension positions. Statistical comparisons were performed using t-tests, with p-values < 0.05 considered significant. A total of 80 neutral and 69 flexion-extension MRIs were analyzed. Patients in the FMSS group displayed significantly smaller minimal cord and canal diameters across all positions compared to the Non-FMSS group (p < 0.001). SAC measurements were also significantly smaller in the FMSS group. Changes in ADI between flexion and extension were modest and not clinically significant. Interobserver reliability was high across all measured parameters. This study provides preliminary normative data for craniocervical junction parameters in pediatric patients with achondroplasia, highlighting key differences between those with and without symptoms of foramen magnum stenosis. The findings suggest that SAC, minimal cord, and canal diameters may serve as valuable measurements for evaluating cervical stenosis in this population. Further research with larger cohorts and standardized protocols is necessary to validate these parameters.