Uroliths are commonly referred to as “stones” and can occur in any section of the urinary tract. Urinary bladder stones are common in both our canine and feline patients. Regardless of specific type, they occur when the urine becomes too concentrated with certain components (precursors like crystals or mucous) and the environmental conditions of the bladder are appropriate for their formulation. Two main types of bladder stones exist: struvite and calcium oxalate stones. These types of stones are normally visible on radiographs (X-rays), though there are a few less common types that do not show up on X-rays. Often there are also crystals in the urine of a bladder with stones, but the type of crystals does not always correlate with the type of urinary stone.
Struvite stone tend especially to form in urine that is alkaline (higher pH). Dogs that are found to have struvite’s commonly have urinary tract infections (UTIs). In cats, the presence of struvite’s is not as closely associated with a urinary tract infection, though infection can still be present. They can sometimes be dissolved with diet changes aimed at change the pH of the urine and diluting the urine, though this can take a long period of time. As stones get smaller with diet modification, there is a risk they will become lodged in the urethra (the tube that carries urine from the bladder to outside the body) and cause a life threatening urinary obstruction. Because of this risk, many veterinarians recommended surgical removal of the stones at the time of diagnosis with diet changes after surgery to prevent additional stones from forming. If you suspect your pet has a urinary blockage or is having trouble urinating, please contact your veterinarian immediately, this can be a life threatening condition and requires immediate attention.
Calcium oxalate stones form in concentrated urine with more acidic urine (lower high pH). They are not normally dissolvable with diet and require surgical removal. It is important to follow up surgery with diet change to keep the urine dilute enough to prevent the reformation of calcium oxalate stones.
There are a few other types of stones that are less common in our veterinary patients. Some animals have genetic predisposition for forming these less common stones. Underlying liver problems can also cause the formation of certain types of urinary stones. Additional testing, by your veterinarian, may be required if these types of bladder stones are suspected.
After surgical removal or dietary dissolution of a stone, follow up with your veterinarian is important to ensure you are doing everything you can to prevent their reformation. Frequent checks of urine pH and urine concentration are important to monitor the efficacy of diet on modification of the bladder environment. It is also important to ensure that the bladder is free from infection to decrease risk of additional stone formation (especially struvite’s). This is done by culturing (trying to grow bacteria) from a urine sample that is obtained through a sterile collection process (cystocentesis). Your veterinarian will guide you through the follow up plan best formulated to keep your pet stone free.