Fig. 1

3D multi-planar reconstruction of tonsillar position (TP, red) morphometric measurement for a T2-weighted MRI of subject 27 in this study: A mid-sagittal plane with McRae’s line shown as a violet line. B Coronal plane with orientation of McRae’s line shown as violet line. C Axial plane visualization through McRae’s line showing partial obstruction of cerebrospinal fluid (CSF) space around the spinal cord