BLADDER STONES (CALCULI) IN DOGS

What are bladder stones?

Bladder stones, also more correctly known as uroliths or cystic calculi, are rock-like collections of mineral that form in the urinary bladder. They may occur as a large single stone or as collections of stones the size of large grains of sand or gravel.

Are these the same as gallstones or kidney stones?

No, gallstones, kidney stones and bladder stones are quite different from each other. Although the kidney and bladder are both part of the urinary system, they are usually unrelated to each other.

What problems do bladder stones cause?

The two most common signs of bladder stones are haematuria (blood in the urine) and dysuria (straining to urinate). Haematuria occurs because the stones mechanically irritate the bladder wall, causing bleeding from its surface. Dysuria occurs when the stones obstruct the passage of urine out of the bladder. Large stones may cause a partial obstruction at the point where urine leaves the bladder and enters the urethra; small stones may flow with the urine into the urethra and cause an obstruction there. When an obstruction occurs the bladder cannot be emptied and this is very painful, your dog may cry in pain; especially if pressure is applied to the abdominal wall.

Haematuria and dysuria are the most common signs seen in dogs with bladder stones, but with obstruction there is usually pain as well. We know this because when bladder stones are removed surgically, many owners state how much happier and more active their dog becomes.

Why do they form?

There are several theories to explain the formation of bladder stones; each is feasible in some circumstances but there is probably an interaction of more than one theory in each individual dog.

The most commonly accepted theory is called precipitation-crystallisation theory; this states that one or more stone-forming crystalline compound is present in elevated levels in the urine. This may be due to abnormalities in the diet or due to some previous disease in the bladder, especially bacterial infections. Occasionally the condition is due to a fault in the body chemistry. When the amount of this compound reaches a threshold level, the urine is said to be supersaturated. This means that the level of the compound is so great that it cannot all be dissolved in the urine, so it precipitates and forms tiny crystals. These crystals stick together usually due to mucus-like material within the bladder and stones gradually form, as time passes they increase in size and number.

How fast do they grow?

Growth will depend on the quantity of crystalline material present and the degree of infection. Although it may take months for a large stone to form, sizeable stones have been documented to form in as little as two weeks.

How are they diagnosed?

Most dogs that have bladder infections do not have stones; these dogs will have blood in their urine and be straining to urinate similar to those with stones. Therefore we do not suspect bladder stones based on these clinical signs alone. Some bladder stones can be palpated (felt with the fingers) through the abdominal wall; however failure to palpate them does not rule them out of diagnosis. Most bladder stones are visible on radiographs or an ultrasound examination; these procedures are performed if stones are suspected. Dogs that show unusual pain when the bladder is palpated, with recurrent haematuria and dysuria or dogs with recurrent bacterial infections of the bladder must be diagnosed accurately.

How are bladder stones treated?

There are two options for treatment, the fastest being to remove the stones surgically. This however requires major abdominal surgery where the bladder is opened and stones removed. Recovery period is two to four days in which the dog is relieved of pain and dysuria and after a few more days haematuria resolves also. Surgery is not always the best option for all patients, however those with urethral obstruction and those with bacterial infections associated with the stones should be operated upon unless other risk factors prohibit surgery. The second option is to dissolve the stones with a special diet, however this has three disadvantages:

1. It is not successful for all types of stones; unless some sand-sized stones can be collected from the urine and analysed, it is not possible to know if the stone can be dissolved..

2. The process is slow; it may take several weeks or a few months to dissolve a large stone and your dog may continue to have haematuria and dysuria during that time.

3. Not all dogs will eat the special diet. This diet needs to be consumed exclusively to work. As it isn't as tasty as the food that many dogs are used to, your dog may not eat it.
   
   

Can bladder stones be prevented?

The answer is a qualified yes! There are at least four types of bladder stones based on their chemical composition. If stones are removed surgically or if some small ones pass in the urine they should be analysed for their chemical composition. This allows your veterinarian to determine if a special diet will be helpful in preventing recurrence. If bacterial infection has caused the stone formation, it is recommended that periodic urinalysis and urine cultures be performed to determine when antibiotics should be given.