Could a dog’s skull shape tell us something about a spinal condition?

A new Cornell University study helps deepen the understanding of skull shapes within different sized dogs and draws a link between cranial and facial shapes, body weight and the risk of syringomyelia, a spinal condition common in some dog breeds.

“We wanted to better characterize what happens to skull shape when you shrink dogs down, so we don’t misdiagnose normal findings as pathologic processes,” said Dr. Peter Scrivani, professor of clinical sciences and corresponding author of the study.

The researchers reviewed the medical records of 852 dogs of varying breeds who had received CT scans of their heads and did not have a known cranial disease.

“This study provides strong evidence that when dogs get smaller, they don’t reduce in size proportionately or isometrically, they actually have a recognizable shape change, which is allometric scaling,” Scrivani said. “We’re not just looking at a miniature wolf-like skull. We’re actually seeing that as the dog shrinks, the cranium undergoes ballooning of the vault that holds the brain, creating a rounder shape.”

Similar shape changes are observed in dogs with altered fluid balance in the central nervous system like hydrocephalus and syringomyelia, a painful condition in which fluid-filled cavities form in the spinal cord. The data showed that breeds predisposed to syringomyelia have a high cranial index. The condition is most common in breeds such as Cavalier King Charles spaniels, Affenpinschers, Brussels Griffons, Chihuahuas and Pomeranians.

“For every 2.2 pounds of body weight that you reduce, there’s a 25% increase in the risk of being in a group that’s going to get syringomyelia,” Scrivani said, “and the shorter and wider the cranium is, the higher risk you have of being in that group.”

Further research is needed to understand if bony changes to the cranium and face contribute to syringomyelia or are a consequence of the disease process, Scrivani said. That understanding could inform treatment and breeding strategies.

“This is a study on associations,” he said. “We don’t prove cause and effect, but we identify things that may be related, or that are related, at least statistically, and then we provided different possibilities for why these associations may have been observed.”

For additional information, see this Cornell Chronicle story. Read the full study here 10.1111/vru.70178