MRI
The cerebellar tonsils are herniated through the foramen magnum (10 mm below the foramen magnum) with obliteration of the cisterna magna. A central cystic cavity of the cervical spinal cord of low signal intensity on T1WI, and high signal intensity on T2WI, extending from C2 up to C6/C7 in keeping with a syrinx. A T2 hypointense area is noted within the syrinx, not visible on axial gradient echo representing most likely a proteinaceous material. A C1/C2 vertebral fusion is noted.
A lacunar infarct of the pons is noted as a small focal area of low signal on T1WI, and high signal on T2WI