Increased hindbrain motion in Chiari I malformation patients measured through 3D amplified MRI (3D aMRI)

Chiari Malformation type 1 (CM-I) is a neurological disorder characterized by morphological defects including excessive cerebellar tonsillar ectopia and associated manifestations. We used 3D amplified MRI on a cohort of healthy and CM-I subjects to investigate the brain’s intrinsic motion, its association with the morphology and patient’s symptomatology, and surgical outcomes. We observed that the regional brain motion in CM-I was significantly higher than that of the healthy subjects, with anterior-posterior (AP) and superior-inferior (SI) displacements in cerebellar tonsils and medulla having the highest differences between the healthy and CM-I ($\sim$45%–$\sim$73% increased motion in the CM-I group). Interestingly, we found the ratio of neural tissue in the foramen magnum to be directly correlated with the SI tonsillar motion ($r=0.58$). Tonsillar herniation was directly correlated with the AP motion of the tonsils ($r=0.61$), and AP and medial-lateral (ML) motions of the medulla ($r=0.66$, and $r=0.57$). Subjects with higher tonsillar ML motion prior to surgery showed improved outcome ($p=0.03$, and $AUC=0.95$). Although we did not observe a significant correlation between the brains motion and morphometrics on the CM-I symptoms (perhaps due to our small sample size), illustrative cases increase our hope for the development of a future tool based on brain biomechanics.