There are many causes of cystitis in dogs. The most common cause is a bacterial urinary tract infection. Other causes include bladder stones, which rub the bladder wall and cause damage, bleeding, and even partial blockage of urine flow. Polyps are masses of tissue that can grow in the bladder and cause inflammation. Tumors also can cause problems with the bladder, including bleeding and sometimes partial blockage of urine flow.
A diverticulum, another cause of cystitis, is an anatomical defect within the bladder in which a pocket forms in the bladder wall. These defects can be microscopic or large enough to see on an x-ray. Growth of bacteria can occur within the urine that collects in these pockets, resulting in a urinary tract infection.
