Novel MRI and histopathological findings in a young Bullmastiff cross dog with mitochondrial fission encephalopathy.

A 9‐month‐old male Bullmastiff cross dog was presented with a history of progressive proprioceptive ataxia and behavior changes. Neuroanatomical localization was multifocal with forebrain and vestibulo‐cerebellum involvement. MRI identified moderate diffuse cerebral sulci widening, dilation of the ventricular system, and rounded, well‐defined, bilaterally symmetrical T2W, FLAIR, and T2* hyperintense intra‐axial lesions affecting the olivary nuclei. Histopathological examination was indicative of a primary mitochondrial disorder. This was confirmed following genetic analysis which identified mitochondrial fission encephalopathy with a homozygous frameshift variant in the MFF gene. This case report documents diagnostic imaging and histopathological findings not previously reported in dogs affected with mitochondrial fission encephalopathy, suggesting a different selective regional vulnerability of the neurons. [ABSTRACT FROM AUTHOR]