A 15-month-old, male neutered Japanese Chin dog was presented for evaluation of blindness and an abnormal gait first observed at 11 months of age. On presentation, the dog was periodically obtunded and had cerebellar ataxia with spastic, hypermetric postural reactions. The dog had an absent menace response and ventro-lateral strabismus in both eyes.A magnetic resonance imaging (MRI) examination was performed with a 3.0 T MRI unit a and a receiveonly quadrature knee coil, and consisted of turbo spin echo sequences with T2-weighting (T2W), and fluid attenuation inversion recovery T2-and T1-weighting (T2W FLAIR & T1W FLAIR) and gradient echo sequences (FSPGR, fast spoiled gradient echo; fast imaging employing steady state acquisition, FIESTA). The T1W FLAIR images were acquired before and after the IV administration of gadolinium-based MRI contrast (Magnevist, b 0.1 mmol/kg). The distinction between gray and white matter regions of the cerebrum and cerebellum was diminished to absent on T2W images (Fig 1). Bilaterally, small regions of more normal-appearing corona radiata were identified in the frontal lobes and rostral internal capsule. In the cranial cervical spinal cord, gray matter was indistinguishable from white matter. On the precontrast T1W FLAIR images, cerebral white matter was hyperintense to gray matter and had ill-defined margins. The cerebral sulci may have been mildly widened for the age of the patient, but the interthalamic adhesion and cerebellar folia were of the appropriate proportions (Fig 1). In addition, the lateral and third ventricles were subjectively dilated. Specifically, a focal enlargement of the caudodorsal aspect of the 3rd ventricle was noted, adjacent to a very small more caudal fluid accumulation, sometimes referred to as a supracollicular intra-arachnoid diverticulum. No abnormal enhancement was observed on postcontrast images. Spectroscopy c was performed in the cerebellar white matter, by a point resolved spectroscopy (PRESS) pulse sequence (Fig 2) and showed a decrease in the N-acetylaspartate (NAA) peak and NAA/creatine (NAA/Cr) ratio in the cerebellar white matter, compared with the normal dog cerebellum. The choline/Cr (Cho/Cr) and the Ch/NAA ratios were higher in the affected dog.The owner elected for euthanasia, and a necropsy was performed. Formalin and fresh frozen samples were collected. Using hematoxylin and eosin staining, the gray matter of the cerebrum and spinal cord was diffusely pale. Approximately 95% of the neurons throughout the cerebrum and dorsal and ventral horn of the spinal cord were up to 4 times larger than normal. These neurons contained abundant finely granular, foamy cytoplasm, which often displaced the nucleus and the Nissl substance to the periphery (Fig 3). Occasional swollen neurons contained dark basophilic nuclei consistent with neuronal degeneration. Many glial cells contained variably vacuolated cytoplasm. Primarily within the white matter of the spinal cord, axons were swollen with dilated myelin sheaths. Fragmented axons were replaced by eo...