Effects of Chiari malformation pinpointed
Dogs with Chiari malformation had taller foreheads and changes to the shape of the brain.
A new study has pinpointed the effects of Chiari malformation on the shape of dogs' skulls and brains.
As a result of selective breeding the condition has become widespread, affecting many toy dog breeds that have been bred to look more doll-like.
Scientists from the University of Surrey took skull, brain and vertebrae measurements from 155 griffon Bruxellois, comparing dogs with Chiari malformation to unaffected dogs.
According to the research published in PLOS One, dogs with the condition had taller foreheads and differences in the shape of the brain. In severe cases, the cerebellum had been pushed underneath the main part of the brain.
While the condition can be asymptomatic, experts say many dogs can suffer from headaches, difficulty walking and even paralysis.
Lead author Dr Clare Rusbridge, from the university's new School of Veterinary Sciences, said: "Chiari malformation can be described as trying to fit a big foot into a small shoe. It can be very painful, causing headaches and pressure on the brain and can result in fluid filled cavities in the spinal cord."
The condition affects a number of toy breeds as well as griffons, including cavalier King Charles spaniels, Chihuahuas and their crosses.
"We want to engage breeders and give them practical advice about the condition," Dr Rusbridge said. "It is also important the public recognises that breeding dogs in a certain way to influence how they look might not be in the animal’s best interest.
"There are responsible breeders out there, who have invested in screening and who are breeding for health as well as producing attractive puppies, and it is vital that people only look to buy from them."
Chiari malformation also affects 1 in 1280 humans. When certain skull bones are fused too early, parts of the brain are pushed through an opening in the base of the skull.
Research being carried out by Surrey scientists and human geneticists from the University of Montreal hopes to improve understanding of the condition, leading to better treatments for both dogs and humans.
Dr Rusbridge commented: "Our latest discoveries will be significant in driving this research forward and will hopefully allow us to identify which genes may be associated with the condition.
"Our next steps will be to apply our technique to other breeds with Chiari malformation and investigate more sophisticated ways of screening, so that risk of disease can be detected more easily, at an earlier age and with a single MRI scan."
The research has been published in PLOS One and can be viewed here.
The BSAVA has opened submissions for the BSAVA Clinical Research Abstracts 2026.
