Dog and cat sharing pet bed
Photo courtesy of Dr. Teri Ann Oursler
Bladder stones, also known as urolithiasis or cystolithiasis, are solid mineral deposits that form inside the bladder of dogs and cats. Stones start out as crystals that form in the urine. These crystals form when a combination of events takes place, such as urine pH change (pH is a measure of acidity and alkalinity in urine), increased urine concentration, and changes in the mineral makeup of the urine being formed. Over time, the crystals combine and layer together to form bladder stones.
Bladder stones can range from one or two stones to hundreds. Some bladder stones are small and grit-like, whereas others can grow to be larger than 2 inches in diameter. Bladder stones are quite common in dogs and cats. Kidney stones, more common in humans, occur much less frequently in dogs and cats. Only 2% of stones found in the urinary tract of our pets are found in the kidney.
The two most common types of bladder stones are those made of calcium oxalate and those made of struvite (also known as magnesium ammonium phosphate). Urate is another mineral type that can form bladder stones but it is rare.
Types of Bladder Stones
Struvite bladder stones can occur with bladder infections. Certain bacteria will change the urine’s pH to grow and replicate better. This pH change causes the urine to be more alkaline, promoting struvite crystals to form. Struvite stones can also form without an infection, which is seen more commonly in cats than dogs.
Less is known about why struvite stones form without an infection. They often play a role in idiopathic cystitis in cats (also known as feline lower urinary tract disease), a condition associated with stress and straining to urinate.
Calcium oxalate stones tend to form with a more acidic pH and are rarely caused by bacteria. Other types of stones can occur with toxins, such as antifreeze poisoning, or can be breed-related as occurs in Dalmatians.
Symptoms of bladder stones include straining to urinate; urinating small amounts more frequently; dribbling urine; urinating in unusual places such as inside the house if house-trained or outside the litter box; vocalizing or crying when urinating; and frequently licking the vulva or penis. The urine may have a strong odor and may have mucus or blood in it.
To diagnose bladder stones, a veterinarian will perform a thorough physical examination. Sometimes large stones can be felt by the veterinarian when assessing for internal organ structures of the abdomen (called abdominal palpation). Urine can be obtained to look for crystals, pH changes, and evidence of infection. X-rays are almost always necessary to confirm bladder stones. Unfortunately, some stones do not show up well on x-rays, so the veterinarian will also need to take into account the symptoms, physical exam, and urine findings.
Determining the type of mineral in the stone is difficult when looking at its shape or appearance. Urine pH can provide clues, but this is not very accurate. To determine the stone’s composition, it must be sent to a special laboratory, and results can take several weeks.
Any infection will need to be treated. Removing bacteria that adjust the pH essentially prevents new stones from forming. Very small stones may dissolve with normalized pH. Unfortunately, large stones create a great environment for bacteria to live, so antibiotics may not be able to completely kill off all the bacteria. Giving antibiotics in situations where all bacteria cannot be killed can potentially cause antibiotic-resistant bacteria. That can make infection harder to control, even after bladder stones are gone.
In some cases, usually with small stones, and in combination with antibiotics for bacteria, struvite stones can be dissolved by feeding a therapeutic diet from your veterinarian. This diet acidifies urine pH and restricts certain minerals such as magnesium and phosphorus. Dissolving the stones can take one week to 2 months, depending on many factors. Calcium oxalate crystals cannot be dissolved with diet, but certain therapeutic diets can change the urine environment such that enlargement or new stone formation is less likely.
Sometimes, bladder stones migrate along the urinary tract and become lodged in the urethra, which is the tube that leads from the bladder to outside the pet’s body (to the hole from which they urinate). In such cases, the pet is at serious risk of a urethral blockage, which prevents the pet from urinating. When this occurs, a method called retropulsion (also called retrograde hydropulsion) may be attempted. A urinary catheter is inserted into the urethra and sterile saline (and sometimes lubricant) are injected into the catheter to try to propel the urethral stones into the bladder to allow for easier removal.
Sometimes veterinarians will use retropulsion to try to remove small stones from the bladder itself (in which case it may be called voiding hydropropulsion). The increased pressure of additional fluid in the bladder allows for small stones to pass easily and quickly out of the bladder and through the urethra with the extra fluid once the catheter is removed.
If hydropulsion does not work and diet change is not an appropriate option for the pet, surgery is needed to remove the bladder stones. This type of surgery is called a cystotomy. The veterinarian surgically opens the abdomen and bladder to physically remove the stones. Stitches or staples are used to close surgical sites.
After surgery, recovery can take 2-4 weeks. Pets will often need pain medication for at least one week to control both the pain and inflammation. Pets are usually given antibiotics after surgery if they had a urinary tract infection. Remember, more stones will form if the infection is not cured. Pets will need to be on restricted activity (no exercise, no running in the house, going outside only on leash even to use the bathroom) for 1-2 weeks following the surgery so they don’t damage the surgical sites or break internal stitches. Urine may be blood-tinged for several days following surgery. The straining should improve by 2-3 weeks after the surgery.
Lithotripsy, a method to fragment stones into a smaller size so they can be passed or removed through the urinary tract, is extremely uncommon in veterinary medicine. The procedure is only available at a few referral institutions and veterinary schools.
Increasing water intake, either by providing more water or adding canned food, can also help treat bladder stones. Increased water allows for increased flushing of the bladder and dilution of minerals within the urine.
Inability to urinate is a life-threatening situation.
If left untreated, bladder stones can grow to the point that urinating is difficult or impossible. This difficulty is especially problematic if stones become stuck in the urethra. Inability to urinate is a life-threatening situation. Other issues associated with bladder stones are chronic pain and an increased risk of urinary tract infections.
Once your pet has had bladder stones, therapeutic diets selected for that specific stone can help prevent recurrence. It is extremely important that only the therapeutic food be given to the pet. No additional treats (unless specific for the diet), bones, or flavored chew toys can be given. Even a small change in the diet can change the pH and mineral content of the urine and lead to the stones reforming. Increase water consumption as much as possible to help dilute the urine to further decrease chances of bladder stone formation.