Cerebrospinal fluid dynamics patterns on MRI to differentiate between simple and complex Chiari 1 malformation

Introduction: Complex Chiari malformation is a more severe variant of Chiari malformation type 1 (CM1), that requires a different surgical approach. Objective: To evaluate whether cerebrospinal fluid (CSF) dynamics on phase-contrast MRI (PC-MRI) can distinguish between simple (SCM) and complex (CCM) subtypes of CM1. Method: This retrospective study included 25 pediatric patients with CM1 and pre-surgical PC-MRI, who underwent surgery from 2013 to 2021. Three independent evaluators diagnosed CCM and classified CSF dynamics into six patterns based on anterior and/or posterior flow alterations. t-test, χ2 or Fischer test, and kappa coefficient, were used for analysis. p < 0.05 was considered statistically significant. Results: Eleven patients (44%) met the criteria for CCM. Patterns 0, 1 and 2 were common in SCM (77.7%) and absent in CCM. Patterns 4, 5 and 6 were predominant in CCM (27.3, 9.1 and 63.6%, respectively), versus 7.1% (each) in SCM. Anterior CSF flow blockage was found in 90.9% of CCM patients, compared to 14.3% in SCM (p < 0.001). The interobserver agreement was high (kappa: 0.79-0.92). Conclusions: Anterior circulatory blockage, alone or with posterior blockage, is more frequently observed in CCM.