Occasionally, cats will have actual stones form in the bladder that cause the obstruction. (bracpet.com)
Although this type of stone is not readily dissolved by dietary modification, it is possible to reduce the risk of stones forming if a specific diet is fed to dogs. (creeksideanimalclinic.com)
Canine bladder stones form when the urinary system is not able to keep the urinary tract free of crystals and infection. (dog-health-handbook.com)