Abstract
Corpus callosum abnormalities (CCA) rarely occur in dogs and are related to hypo/adypsic hypernatremia and seizures. Hypoplasia and dysplasia of the corpus callosum (CC) with concomitant lobar holoprosencephaly is the most common variant. It is currently uncertain using conventional MRI if canine CCA reflects the failure of commissural fibers to develop or the failure of the commissural fibers to cross hemispheres. Diffusion tensor imaging was performed in a 4-year-old Staffordshire mix breed dog with CCA and an age-matched healthy Beagle. In comparison to the control dog, CC tractography of the affected dog depicted only axonal tracts corresponding to the temporal CC fibers. The cingulum bundles appeared supernumerary with unorganized architecture, extending into the ipsilateral cerebral cortex, and therefore strongly suggested homology to Probst bundles reported in humans with CCA. The presence of Probst bundles in canine CCA could represent compensatory neuroplasticity-mediated networking and may contribute the fair prognosis reported in affected dogs.
Highlights
Corpus callosum abnormalities (CCA) occur sporadically in dogs and are classified into hypoplasia with or without concomitant dysplasia and agenesis [1]
The Magnetic resonance imaging (MRI) of the brain revealed a discrete area of preserved thickness and signal intensity of white matter at the level of the splenium and a non-detectable rostrum, genum and corpus (Figure 1)
Tractographies originating from Region of interest (ROI) placed at the corpus callosum (CC) in the control dog revealed the presence of frontal orbital, anterior and superior parietal, occipital, and temporal CC fibers; whereas only temporal fibers could be depicted after analyzing the same ROIs in the dog affected by CCA (Figures 2C,D)
Summary
Corpus callosum abnormalities (CCA) occur sporadically in dogs and are classified into hypoplasia with or without concomitant dysplasia and agenesis [1]. Dogs affected with CCA commonly present a mild degree of lobar holoprosencephaly (HPE) [2]. In veterinary medicine, it is currently uncertain if CCA in dogs reflects a failure of commissural white matter tracts to develop or a failure to cross the midline and to connect both cerebral hemispheres [1]. In humans affected by CCA, white matter bundles of the cingulum undergo morphological remodeling, thereby changing their trajectory and allowing them to have a wider connectivity within the ipsilateral cerebral hemisphere [3]. The present case report describes the morphology and integrity of the corpus callosum and cingulum in a dog affected by CCA. The evaluation of T1W, T2W, and the tractography analysis of DTI images were performed using free available software (Horos Project, version 2.2.0, horosproject.org; ExploreDTI, version 4.8.6, Utrecht) [8]
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