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

Abstract

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.

Corpus callosum abnormality in a puppy with hypernatraemia

“…2 That study documented the presence of Probst bundles in dogs with CCA, suggesting that axons involved in the pathogenesis had formed normally but failed to cross the midline. 2 Previously documented in humans with CCA, Probst bundles are axonal fibres that have undergone morphological remodelling and change their trajectory to extend from the cingulum to various areas of the cerebral cortex, thereby providing a greater degree of connectivity within the ipsilateral cerebral hemisphere. Probst bundles are thought to represent a mechanism of compensatory neuroplasticity.…”

“…However, a recent study used diffusion tractography to study the embryologic origin of a CCA in a coonhound, and results suggested an alternative hypothesis 2 . That study documented the presence of Probst bundles in dogs with CCA, suggesting that axons involved in the pathogenesis had formed normally but failed to cross the midline 2 . Previously documented in humans with CCA, Probst bundles are axonal fibres that have undergone morphological remodelling and change their trajectory to extend from the cingulum to various areas of the cerebral cortex, thereby providing a greater degree of connectivity within the ipsilateral cerebral hemisphere.…”

“…1 Although failure of axonal formation was previously suspected in the pathogenesis of CCA, recent evaluation of diffusion tractography in a dog with a CCA suggests that the pathogenesis actually involves failure of formed axons to decussate and form Probst bundles. 1,2 Staffordshire bull terriers and schnauzers appear to be predisposed, although CCAs have been reported sporadically in other breeds, including a standard poodle. 1,3…”

“…Many dogs have concurrent fusion of midline structures that are involved in thirst regulation, such as the hypothalamus and cingulate cortex, which may contribute to the adipsia/hypodipsia noted in these cases 1 . Although failure of axonal formation was previously suspected in the pathogenesis of CCA, recent evaluation of diffusion tractography in a dog with a CCA suggests that the pathogenesis actually involves failure of formed axons to decussate and form Probst bundles 1,2 . Staffordshire bull terriers and schnauzers appear to be predisposed, although CCAs have been reported sporadically in other breeds, including a standard poodle 1,3 …”

Characterizing the canine and feline optic pathways in vivo with diffusion MRI

“…All subjects' diffusion data were preprocessed and modeled using pipelines as described in previous literature 34 . Subjects' tensor maps for each diffusion metric were obtained, inspected visually for quality assurance, and found to be within normal quantitative ranges (for example, FA metric being between 0 and 1) from previous feline and canine diffusion literature 35,36 …”