Figure 1: Sagittal T1W (A) and T2W (B) MR images of a patient with Arnold- Chiari malformation type I. The cerebellar tonsils protrude through the foramen magnum (broken line), and an associated syrinx is present. The fourth ventricle is normal, and there is no meningocele or other structural defect. (C), the herniation of the cerebellar tonsils (white arrows) is seen on the axial T2W MR image taken through the level of C1. (D), the syrinx is also well demonstrated on the axial T2W MR image taken through the midcervical spine.