The use of diffusion tractography to characterize a corpus callosum malformation in a dog.

Introduction: The pathogenesis of corpus callosum malformations (CCM) is not well defined in the dog because of inherent limitations of structural magnetic resonance imaging (MRI) to evaluate the white matter. We used the advanced neuroimaging technique of tractography to virtually dissect the white matter projections in a dog with a CCM and in a normal control dog.

Methods: A 9-month-old male Coonhound that had a previous structural MRI diagnosis of CCM and a normal control dog underwent anesthesia and 3-Tesla MRI. Diffusion-tensor imaging and 3D T1-weighted and 2D T2-weighted sequences were acquired. Diffusion data were processed before tensor reconstruction and fiber tracking. Virtual dissections were performed to dissect out the major white matter projections in each dog.

Results: In the dog with CCM, the corpus callosum exhibited interhemispheric crossing fibers at the level of the splenium and formed longitudinal callosal fasciculi (Probst bundles). In addition, the fornix was small and the cingula enlarged and exhibited increased dorsal connectivity relative to the normal control.

Conclusions And Clinical Importance: We used tractography to describe a white matter malformation in a dog. The results suggest that, embryologically, formed axons fail to cross midline and instead create Probst bundles.