Brain Volume Analysis and Identification of Cerebellar Atrophy in Different Breeds of Dogs Using Magnetic Resonance Imaging
Neurodegenerative diseases affecting the cerebellum are well documented in several different breeds of dogs. When extreme, the cerebellar atrophy associated with such diseases can be detected on magnetic resonance imaging (MRI). However, there is little published information regarding the changes in cerebellar size that occur with age or relating its volume and cross sectional area (CSA) to other regions of the brain in different breeds. As a result, identification of cerebellar atrophy on MRI is subjective. We hypothesize that the CSA of the cerebellum on mid-sagittal images maintains a consistent ratio with CSA of other regions of the brain in all breeds of dogs of all ages and that this ratio can be used to identify cerebellar atrophy on MRI.
The proportions of the volumes and mid-sagittal CSA of the forebrain, brainstem, and cerebellum were quantified and compared in different breeds and ages of normal dogs and in dogs diagnosed with cerebellar degenerative disorders. Brain MRIs of normal dogs were obtained from the IAMs Pet Imaging Centers' database. Images of dogs diagnosed with cerebellar degenerative disorders were recruited from neurologists. All images were uploaded into the OsiriX DICOM viewer program. The CSA of the forebrain, brainstem, and cerebellum was manually traced from every T1 weighted axial image and the T2 weighted mid-sagittal image. Volumes of each brain region were calculated from the axial images by multiplying the CSA of each image by the slice thickness. Comparisons between groups were made using the student's t test.
Four groups of normal dogs aged from 5-10 years (Labrador Retrievers (n=10), Beagles (n=8), toy breeds (n=10) and brachycephalics (n=7)) were compared. The volumes of the different brain regions as well as total brain volumes were different between breeds, but the proportion of each region to the total brain volume was not significantly different. The same trend was observed when comparing the mid-sagittal CSAs. Labrador Retrievers from three different age groups were compared to evaluate the effect of age on cerebellar size. There was no observed effect of age on the relative size and proportion of the cerebellum in these dogs. The ratio of the mid-sagittal CSA of the cerebellum to the CSA of the brainstem was consistent between different breeds and ages of dogs. This ratio was calculated in 15 normal and 22 American Staffordshire Terriers diagnosed with cerebellar degeneration and was significantly different between these two groups (p<0.0001). The ratio was also calculated in an affected Scottish Terrier and an Old English Sheepdog and clearly identified cerebellar atrophy in both dogs. We conclude that the ratio between the cerebellar and brainstem mid-sagittal CSA is a useful indicator of cerebellar atrophy in dogs. CSA can readily be measured from MRI making this a rapid and accessible diagnostic test.