Cavalier King Charles Spaniels have extremely high rates of syringomyelia and Chiari-like malformation, caused by selective breeding for a domed skull shape that leaves insufficient space for the brain, causing chronic severe pain.
Cavaliers with syringomyelia experience phantom scratching (scratching at the air beside their neck), vocalisation, and signs of constant neurological pain that is extremely difficult to manage. The condition is progressive and the dog may spend years in chronic pain before terminal deterioration. Breeding for skull shape that causes this suffering in the majority of the breed represents one of the most significant welfare failures in pedigree dog selection.