Cardiac-related spinal cord tissue motion at the foramen magnum is elevated in Type I Chiari malformation patients and decreases post-decompression surgery

Objective— Type 1 Chiari malformation (CM-I) is a craniospinal disorder historically defined by cerebellar tonsillar position (TP) greater than 3-5mm below the foramen magnum (FM). This definition has come under question since quantitative measurements of cerebellar herniation do not always correspond with symptom severity. Researchers have proposed several additional radiographic diagnostic criteria based on dynamic motion of fluids and/or tissues. The present study objective was to determine if cardiac-related craniocaudal spinal cord tissue displacement is an accurate indicator of the presence of CM-I and if tissue displacement is altered with decompression. Methods— A cohort of 20 symptomatic patients underwent decompression surgery. Fifteen healthy volunteers were recruited for comparison to the CM-I group. Axial phase-contrast magnetic resonance imaging (PC-MRI) measurements were collected pre- and post-surgery at the FM with cranial-caudal velocity encoding and 20 frames per cardiac cycle with retrospective reconstruction. Spinal cord motion (SCM) at the FM was quantified based on the peak-to-peak integral of average spinal cord velocity. Results— Tissue motion for the pre-surgical group was significantly greater than controls (p=0.0009). Motion decreased following surgery (p=0.058) with an effect size of -0.151 mm and a standard error of 0.066 mm. Post-operatively, no statistical difference from controls in bulk displacement at the FM was found (p=0.200) after post hoc testing using Tukey's adjustment for multiple comparisons. Conclusions— These results support SCM measurement by PC-MRI as a possible non-invasive radiographic diagnostic for CM-I. Dynamic measurement of SCM provides unique diagnostic information about CM-I alongside static quantification of TP and other intracranial morphometrics.