Caudal descent of the cerebellar tonsils through the foramen magnum,10 mm below the McRae line on sagittal T1 and T2 sequence with crowding of the medulla by the tonsils on axial sequences. Mild dilatation of the lateral and 3rd ventricles with an abnormal CSF flow dynamics through the central canal of the cord and around the medulla on sagittal and axial flux sequences.
Small vessel ischaemic changes are noted.
No syrinx of the upper cervical cord on sagittal sequences.