Comparison of the Relationship between Cerebral White Matter and Grey Matter in Normal Dogs and Dogs with Lateral Ventricular Enlargement

Abstract

Large cerebral ventricles are a frequent finding in brains of dogs with brachycephalic skull conformation, in comparison with mesaticephalic dogs. It remains unclear whether oversized ventricles represent a normal variant or a pathological condition in brachycephalic dogs. There is a distinct relationship between white matter and grey matter in the cerebrum of all eutherian mammals. The aim of this study was to determine if this physiological proportion between white matter and grey matter of the forebrain still exists in brachycephalic dogs with oversized ventricles. The relative cerebral grey matter, white matter and cerebrospinal fluid volume in dogs were determined based on magnetic-resonance-imaging datasets using graphical software. In an analysis of covariance (ANCOVA) using body mass as the covariate, the adjusted means of the brain tissue volumes of two groups of dogs were compared. Group 1 included 37 mesaticephalic dogs of different sizes with no apparent changes in brain morphology, and subjectively normal ventricle size. Group 2 included 35 brachycephalic dogs in which subjectively enlarged cerebral ventricles were noted as an incidental finding in their magnetic-resonance-imaging examination. Whereas no significant different adjusted means of the grey matter could be determined, the group of brachycephalic dogs had significantly larger adjusted means of lateral cerebral ventricles and significantly less adjusted means of relative white matter volume. This indicates that brachycephalic dogs with subjective ventriculomegaly have less white matter, as expected based on their body weight and cerebral volume. Our study suggests that ventriculomegaly in brachycephalic dogs is not a normal variant of ventricular volume. Based on the changes in the relative proportion of WM and CSF volume, and the unchanged GM proportions in dogs with ventriculomegaly, we rather suggest that distension of the lateral ventricles might be the underlying cause of pressure related periventricular loss of white matter tissue, as occurs in internal hydrocephalus.

Association between improvement of clinical signs and decrease of ventricular volume after ventriculoperitoneal shunting in dogs with internal hydrocephalus

“…Underlying causes include genetic factors, developmental anomalies (eg, aqueductal stenosis), prenatal or postnatal infection, periventricular hemorrhage, or meningitis . It is reasonable to expect that different etiologies affect the speed and severity of ventricular expansion and thereby the grade of functional brain deficits . Variable etiologic factors therefore might have an influence on persistent clinical signs in some dogs, which also limit the interpretation of the results of our study.…”

“…Minor changes of ventricular volume could have been missed in the segmentation process. The validity of our approach would have increased further with multiple examinations, but we did not determine interobserver and intraobserver variability because the manual segmentation process is extremely time‐consuming …”

“…Study numbers were assigned to the dogs so that the observer was blind to the preoperative or postoperative condition at the time of volume determination. To assess if a decrease in volume of the ventricular system and increase in volume of the brain parenchyma occurred, and to measure the amount of decreased volume, the CSF inside the ventricles and the brain parenchyma was extracted from the digital images by manually tracking the boundaries using specialized graphical software (AMIRA; Mercury Computer Systems, Berlin, Germany) as described previously . This program allows accurate manual image segmentation on a slice‐by‐slice basis.…”

“…The total ventricular volume comprised all 4 ventricles, including the choroid plexus. The delineation of both the ventricular system and the brain parenchyma to the spinal cord was set along a vertical line at the obex . Polygonal surface reconstruction algorithms allowed determination of the volumes from the 2‐dimensional images.…”

“…To assess if a decrease in volume of the ventricular system and increase in volume of the brain parenchyma occurred, and to measure the amount of decreased volume, the CSF inside the ventricles and the brain parenchyma was extracted from the digital images by manually tracking the boundaries using specialized graphical software (AMIRA; Mercury Computer Systems, Berlin, Germany) as described previously. 25 including the choroid plexus. The delineation of both the ventricular system and the brain parenchyma to the spinal cord was set along a vertical line at the obex.…”