Urinary Stones, Bladder Stones
Urinary tract stones are a common cause of abnormal urination and abdominal pain in dogs and cats. Pets may have a few large stones, several tiny pebble-like stones, or sandy grit material within the urinary tract. Some stones have sharp, spiky edges and may cause intermittent blood in the urine from trauma to the bladder lining.
Stones can develop anywhere along the urinary tract (kidneys, ureters, bladder, urethra), and depending on the size, may obstruct the ureter or urethra. Obstruction of the ureter or urethra is a medical emergency that usually requires surgical treatment. Stones in the bladder cause pain and act as a place for bacteria to hide from the immune system. Stone removal is often necessary to clear bladder infection in dogs with urinary tract infections (UTI) for this reason.
Pets with bladder stones often present with some of the following clinical signs:
Increase in thirst and urination frequency
Straining to urinate
Cloudy, foul-smelling urine
Blood in the urine
Frequent genital grooming
*If your pet is straining to urinate and is not producing urine, this may indicate an emergency urinary obstruction and should be seen by a veterinarian immediately*
Bladder stones develop from microscopic urinary crystals that combine together to make larger stones. Different types of stones form in different situations. The most commonly diagnosed urinary stones in dogs and cats are: struvite, calcium oxalate, urate, and cystine. Identifying the type of stone in your pet’s bladder helps to determine the underlying cause and aim treatment to prevent future stone development. Stones removed from the bladder are always submitted for analysis to determine their make-up.
How are urinary stones diagnosed?
Physical examination - sometimes bladder stones can be felt on abdominal palpation. Some dogs do not allow bladder palpation because of pain from bladder stones.
Blood work - to evaluate for evidence of infection, check calcium levels, liver, and kidney values.
Urinalysis - to look at the urine chemistry and types of cells and crystals in the urine.
Urine Culture - to diagnose urinary tract infection, and determine the most appropriate antibiotic for treatment.
Abdominal X-rays - to look for bladder stones that are visible on x-ray (struvite and calcium oxalate).
Abdominal Ultrasound - to look for bladder stones that cannot be seen on x-ray (urate, cystine).
Stone analysis - any removed urinary stones are submitted for analysis to determine the type of stone and best follow-up treatment for decreasing future stone formation
Can urinary stones by medically managed?
Medical management of urinary stones is aimed at decreasing the risk of urinary crystal and stone formation, and dissolving stones present in the bladder. Increasing water intake can help prevent the urine from getting concentrated enough to make crystals and stones. Increased water intake can be encouraged by adding additional water to canned or dry food. Canned food has a higher water content than dry food. Prescription diets are available that decrease the formation of urinary crystals and stones by controlling the urinary pH. Additional medications can be used to acidify the urine when necessary. Cystine and urate stones can also be treated with specific medications to reduce the formation of stones. Calcium Oxalate stones cannot be dissolved and must be surgically removed. Struvite stones can take 1-2 months to dissolve with dietary management.
Struvite Stones (magnesium ammonium phosphate)
Struvite stones are the most commonly seen urinary stones in dogs and cats. These stones are very common in female dogs and are almost always caused by a urinary tract infection. The bacteria in the bladder cause the urine to become less acidic and this promotes the formation of struvite stones. These stones can sometimes be dissolved without surgery using a prescription urinary diet and supplements to acidify the urine back to normal levels, as well as an antibiotic to treat the associated UTI. Stones typically take 1-2 months to dissolve. However, some stones fail to dissolve, or the UTI is unable to be effectively treated with the presence of the stones. In these cases, and in dogs with a large number of stones, surgical removal of the stones is recommended. Struvite stones are visible on x-ray. A prescription urinary diet can help reduce the formation of these stones.
Calcium Oxalate Stones
Calcium Oxalate stones form in acidic urine, and cannot be dissolved medically. These stones are more common in male dogs and develop as a result of genetics and/or high calcium diets. They are commonly seen in small and toy breed dogs. Dogs with high blood calcium and calcium oxalate stones should be checked for hyperparathyroidism to rule this out as a cause for the high calcium levels. Removal of the stones is necessary for treatment. Some dogs will develop a secondary UTI due to the presence of the stones that cannot be successfully cleared without stone removal. Calcium Oxalate stones are visible on x-ray. A prescription urinary diet can help reduce the formation of these stones.
Urate Stones (urate, ammonium biurate)
Urate stones are most commonly associated with a congenital liver disorder in small breed dogs called portosystemic shunt. This leads to higher urates in the bloodstream and concentration in the urinary tract which leads to stone formation. Dogs with portosystemic shunts require surgical treatment of the shunt in order to stop the production of urate stones.Dalmations and Bull dogs are also predisposed to developing urate stones because of a genetic abnormality that leads to higher urates in the bloodstream. Dalmations and Bulldogs with urate stones can be treated with a special diet to dissolve and prevent the development of stones. A medication called allopurinol may also reduce the formation of urate stones in dogs with this genetic abnormality. These dogs should not be bred, as they can pass this genetic abnormality to offspring. Urate stones are not visible on x-ray, and are typically diagnosed on ultrasound. A prescription urinary diet can help reduce the formation of these stones.
Cystine stones form in animals with a genetic abnormality that prevents their kidneys from absorbing cystine normally. The result is more cystine in the urinary bladder which begins to form stones. A genetic test is available to confirm the abnormality. These stones form most commonly in male dogs. Some dogs will stop making cystine stones after castration. Cystine stones are not visible on x-ray, and are typically diagnosed on ultrasound. A prescription urinary diet can help reduce the formation of these stones.
For more information about other specific types of stones, visit here.
Are there non-surgical treatments for urinary stones?
Urohydropulsion - Smaller bladder stones that are not large enough to block the urethra can sometimes be removed by anesthetizing the patient, filling the bladder with saline using a urinary catheter, then expressing the bladder repeatedly to force the stones out of the bladder. Repeated x-rays are taken to ensure all stones have been removed. If all stones are not successfully removed using this technique, bladder surgery is performed.
Laser Lithotripsy - Although we do not currently offer this service at CCVS, dogs with a low number of stones that are small or medium can have the stones destroyed by a laser. The laser is used with a small camera that goes up the urethra and into the bladder while the patient is under anesthesia. This technique can be useful in dogs with a stone stuck in the urethra that cannot be removed. Laser lithotripsy is a slow process, and we do not recommend this in dogs with large stones, or many stones to prevent excessive anesthesia times.
What is the surgical treatment for urinary stones?
Surgical exploration of the urinary bladder for stone removal is called cystotomy. This is the most efficient way to treat bladder stones. This procedure involves making an incision in the urinary bladder, evaluation of the bladder tissues and physical removal of stones. A sample of the bladder lining is typically submitted for bacterial culture and sensitivity to evaluate for UTI. X-rays are taken after surgery to ensure that all stones have been removed. Fortunately, the urinary bladder is one of the fastest healing tissues in the body and tolerates surgery very well. In male dogs with stones stuck in the penile urethra that cannot be removed, a procedure called scrotal urethrostomy may be performed. This surgery involves creating a new opening in the urethra before the stone blockage to allow for normal urine flow.