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.

Corpus callosal abnormalities in dogs.

BACKGROUND: Corpus callosal abnormalities (CCA) in dogs have been only sporadically reported and are poorly characterized. HYPOTHESIS/OBJECTIVES: To describe the clinical presentation and magnetic resonance imaging (MRI) characteristics of dogs with CCA. ANIMALS: Fifteen client-owned dogs. METHODS: Retrospective study. Records of the contributing institutions were reviewed to identify dogs diagnosed with malformations affecting the corpus callosum (CC); cases in which the CCA was thought to be secondary were excluded. RESULTS: The most represented breeds were Staffordshire Bull Terriers (5/15) and Miniature Schnauzers (3/15; n = 3, 20%) and the mean age at time of presentation of 19 months (range 3-81 months). The clinical signs most commonly reported were adipsia/hypodipsia with associated hypernatremia (12/15), tremors (6/15), and seizures (6/15). Review of the MR images revealed that 10 dogs had absence of the rostral CC and hypoplasia of the caudal portion, 4 dogs had a diffusely hypoplastic and dysplastic CC, and 1 dog had a diffusely hypoplastic CC. In 14 cases, there was abnormal cortical development with fusion of the ventral frontal lobes and part of the diencephalon, indicating lobar holoprosencephaly. CONCLUSIONS AND CLINICAL IMPORTANCE: Previous literature has mainly associated CCA with adipsia and only 12 of 15 dogs in the current series demonstrated this abnormality. There are different degrees of the malformation but in 10 dogs the rostral portion of the CC is most severely affected. Fourteen dogs have simultaneous fusion of the midline structures rostral to the CC; this region has several structures involved in thirst regulation and might explain this derangement.

Magnetic resonance imaging findings associated with lateral cerebral ventriculomegaly in English Bulldogs.

Multiple congenital or developmental anomalies associated with the central nervous system have been reported in English Bulldogs. The purpose of this retrospective study was to identify and describe the prevalence and MRI characteristics of these anomalies and their association with presence and degree of cerebral ventriculomegaly. Magnetic resonance imaging studies of 50 English Bulldogs were evaluated. Forty-eight dogs had some degree of cerebral ventriculomegaly, 27 of which had an otherwise normal brain. Presence of lateral ventriculomegaly was not significantly associated with presence of another intracranial lesion. Appearance of the septum pellucidum was variable, ranging from intact to incomplete or completely absent. The corpus callosum was subjectively thinned in all but three dogs, two of which had normal lateral ventricles. Fusion of the rostral colliculi was not found in any dog. A persistent craniopharyngeal canal was identified in one dog. Aqueductal stenosis caused by fusion of the rostral colliculi was not identified in any dog. Findings indicated that cerebral ventriculomegaly is a common finding in English Bulldogs with or without other intracranial lesions, aqueductal stenosis caused by fusion of the rostral colliculi is unlikely to be a common etiology leading to obstructive hydrocephalus, and a large craniopharyngeal canal is a rare finding that has unknown clinical significance at this time.

Diverticulum of the third ventricle and absence of the interthalamic adhesion in a dog.

A 10-month-old male Pomeranian dog was examined for neurological abnormalities consistent with diffuse forebrain and cerebellar disease. Based on ultrasound and magnetic resonance imaging (MRI) a diagnosis of diverticulum of the third ventricle, partial agenesis of the corpus callosum, and absence of the interthalamic adhesion was made. As conservative treatment was unsuccessful, a ventriculoperitoneal shunt was placed.