Fig. 4. T-2 weighted sagittal images of three dogs affected by an atlanto-axial subluxation in this study (TE, 120 ms; TR, 3800 ms; slice thickness, 2.5 mm). (A) This dog with atlantoaxial subluxation has intramedullary T2 hyperintensity at the level of compression that likely indicates edema or ischemia (red arrow). Chiari malformation is absent. (B) There is Chiari malformation causing impaction of the cerebellum, with similar intramedullary hyperintensity at the level of compression as in A (red arrow) but additional pre-syrinx formation caudal to the level of spinal cord compression (yellow arrow). This dog was also graded as having moderate hydrocephalus. (C) There is Chiari malformation causing indentation of the cerebellum and focal syringomyelia greater than 2 mm in diameter.