A UK study has identified the specific effect Chiari malformation has on the shape of a dog’s skull and brain, laying the groundwork for early screening.
The prevalence of Chiari malformation (CM) has increased due to selective breeding of brachycephalic toy breeds including Cavalier King Charles Spaniels, Griffon Bruxellois, Affenpinschers and Chihuahuas.
According to the authors of the study, CM is a complex abnormality characterised by overcrowding of the craniocervical junction and a disparity between the brain parenchyma (too big) and the skull (too small). This can result in obstruction of cerebrospinal fluid channels, leading to the spinal cord disease syringomyelia.
“Chiari malformation can be described as trying to fit a big foot into a small shoe,” said lead author Clare Rusbridge from Surrey University’s School of Veterinary Medicine. “It can be very painful, causing headaches and pressure on the brain and can result in fluid filled cavities in the spinal cord.”
In the study, published in PLOS ONE, researchers measured the brains, skulls and vertebrae of 155 Griffon Bruxellois and compared measurements of those with CM to those without.
They found that in Griffons, CM is characterised by a shortening of the entire cranial base, and possibly by increased proximity of the atlas to the occiput. They hypothesise that increased height in the rostral cranial cavity, lengthening of the dorsal cranial vault and considerable reorganisation of the brain parenchyma (including ventral deviation of the olfactory bulbs and rostral invagination of the cerebellum under the occipital lobes) are compensatory changes.
To date variations in morphology in animals with CM add to the difficulty in diagnosis. Early detection means that affected dogs can be desexed prior to breeding, preventing the condition being passed on to offspring.
Rusbridge said that further studies are required to characterise CM in different breeds, but was hopeful that researchers would identify genes behind the condition.
ANNE FAWCETT
Reference:
Knowler SP, McFadyen AK, Freeman C, Kent M, Platt SR, et al. (2014) Quantitative Analysis of Chiari-Like Malformation and Syringomyelia in the Griffon Bruxellois Dog. PLoS ONE 9(2): e88120. doi:10.1371/journal.pone.0088120