What are bladder stones?
Bladder stones (also called uroliths or cystic calculi) are rock-like formations of minerals that develop in the urinary bladder. There may be a large, single stone, or a collection of stones that range in size from sand-like grains to gravel. Many times, there is a mixture of both large and small stones present. All stones form because of disease or inflammation in the bladder.
What are the clinical signs of bladder stones?
The most common signs of bladder stones in dogs are:
- blood in the urine (called hematuria) and
- straining to urinate (called dysuria).
Bleeding occurs because the stones rub against the bladder wall, irritating and damaging the tissues. Straining happens due to inflammation and swelling of the bladder wall or the urethra (the tube that connects the bladder to the outside of the body). Straining may also be caused by muscle spasms.
Large stones may act like a valve, causing a temporary or partial obstruction at the neck of the bladder (the point where the bladder attaches to the urethra). Small stones may flow with the urine into the narrow urethra, where they become lodged and cause an obstruction. A urinary obstruction is usually recognized in a dog that is straining to urinate without producing any urine or is only producing small squirts of urine. This problem occurs more frequently in male dogs because their urethra is much longer and narrower.
If an obstruction occurs, the bladder cannot be emptied fully. This condition is an emergency, and is very painful, especially when pressure is applied to the abdomen. If the obstruction is not relieved, the bladder may rupture. A complete obstruction is life-threatening and requires immediate emergency treatment.
How did my dog get bladder stones?
Certain minerals are naturally found in your dog’s body. When these minerals are not properly processed by the dog’s urinary system, or when these minerals are found at higher-than-normal levels in the urine, they can crystallize. The sharp crystals irritate the bladder lining, causing a production of mucus. The crystals and mucus stick together, forming clusters that gradually enlarge and harden into stones.
Several factors can influence this process. Urine pH (level of acidity), the presence of certain proteins in the urine, and the urine’s water content all affect stone formation. Diet can help change the pH of the urinary environment, predisposing them to crystal formation. Crystals may also form due to some previous disease in the bladder, especially a bacterial infection. Sometimes, the condition may be due to a problem with the body's metabolism.
How quickly can bladder stones form?
Bladder stones can develop within a few weeks or may take months to form. The rate of urolith formation and growth varies, depending on factors such as diet, urine pH, and how much crystalline material is present in the urine.
How are bladder stones diagnosed?
The signs of bladder stones are like those of an uncomplicated bladder infection or cystitis. Most dogs with a bladder infection do not have bladder stones, so veterinarians do not assume a dog has bladder stones based only on these clinical signs.
Some bladder stones can be palpated or felt with the fingers through the abdominal wall. However, failure to feel bladder stones does not rule them out because many are too small to be detected in this way, or the bladder may be too inflamed and painful to allow palpation.
Most bladder stones are visible on X-rays or by an ultrasound exam of the bladder. Some types of bladder stones are radiolucent, meaning they cannot be seen on a normal X-ray, because their mineral makeup does not reflect X-ray beams. They can be detected by an ultrasound examination or with contrast X-rays, a specialized technique that uses dye or contrast material to outline the stones within the bladder.
How are bladder stones treated?
There are three main treatment options for bladder stones: surgical removal, non-surgical removal by urohydropropulsion, and dietary dissolution.
The specific treatment recommended for your dog will depend on the type of stone present. Your veterinarian will discuss the pros and cons of each treatment option with you in more detail, based on your dog's individual circumstances.
Surgery: This is often the quickest way of treating bladder stones; however, it may not be the best option for patients that have other health concerns, or in whom general anesthesia could be risky. With this option, the stones are removed via cystotomy: a surgical procedure to access and open the bladder so that the stones can be removed. This surgery is routine and dogs usually make a rapid postoperative recovery. If the stones have obstructed the urethra such that the dog is unable to urinate, an emergency procedure must be performed IMMEDIATELY to save the dog's life.
Voiding urohydropropulsion: If the bladder stones are very small, it may be possible to pass a catheter into the bladder to fill it and then flush the stones out, using a non-surgical technique called urohydropropulsion. In some cases, this procedure may be performed with the dog under heavy sedation, although general anesthesia is often necessary. This procedure may not work in some cases and may be less effective in male dogs due to urethral anatomy.
Cystoscopy: If your veterinarian has a cystoscope (a very small camera on a long tube), it can sometimes remove small stones in the bladder, thereby avoiding a surgical procedure to open the bladder.
Dietary dissolution: In some cases, bladder stones can be dissolved by feeding your dog a special diet that is formulated to dissolve bladder stones. This diet will be tailored to the specific type of stone present, though most of these diets are now formulated to help prevent the two most common types of crystal or stone formation: struvite and calcium oxalate. Common diets used for this purpose are Hill's Prescription Diet C/D, Purina UR/StOX, and Royal Canin Urinary SO. This approach avoids surgery and can be a good choice for some dogs; however, it has three disadvantages:
- It is not successful for all types of stones. Stone analysis is necessary to determine if it is the type of stone that can be successfully dissolved, and it may not be possible in all cases. Sometimes, your veterinarian will make an educated guess about the type of stone, based on the X-ray appearance and the results of a urinalysis.
- It is slow. It may take several weeks or a few months to dissolve a large stone, so your dog may continue to have bloody urine, straining, and recurrent infections during that time. The risk of urethral obstruction is still present while waiting for the stones to dissolve.
- Not all dogs will eat the special diet. These diets only work if they are fed exclusively, which means that no treats or supplements can be given to your dog while it is on the special diet.
Are there any other treatment options?
Another option for bladder stone treatment is laser lithotripsy. Laser lithotripsy uses a cystoscope to guide a laser to contact the stone. The laser heats up the molecules around the stone, causing the stone to break into tiny particles that can then be flushed out of the bladder or retrieved with a small basket passed through the cystoscope. It allows for immediate removal of the offending stones without the need for surgery.
However, it has limitations that restrict its use, including time required to target multiple stones and the need for a large enough urethra to pass the cystoscope (i.e., it can’t be used in small, male dogs). Your veterinarian will discuss if this is a good treatment option for your dog and if it is available in your area.
Can bladder stones be prevented?
Prevention is possible in some cases. There are at least five types of bladder stones in dogs, each with a different chemical makeup. See handouts on "Struvite Bladder Stones in Dogs", "Urate Bladder Stones in Dogs", "Xanthine Bladder Stones in Dogs", "Cystine Bladder Stones in Dogs" and "Calcium Oxalate Bladder Stones in Dogs" for specific information about the various types of stones. Early recognition may allow your veterinarian to adjust your dog's diet or medication before the need for surgery.
If bladder stones are removed surgically or if small ones pass in the urine, they should be analyzed for their chemical composition, which allows your veterinarian to determine if a special diet or medication is appropriate. See handout "Nutritional Concerns for Dogs with Bladder Stones" for more information.
If the stones formed because of a bacterial infection, it is recommended that periodic urinalyses and urine cultures be performed to detect subclinical recurrences and determine if antibiotics should be prescribed. Periodic bladder X-rays or ultrasounds may be helpful in some cases to determine if bladder stones are recurring.
