Bladder Stones (Urinary Calculi)
What are they?
Calculi or bladder stones are rock-like collections of minerals that form in the urinary bladder. They may be in the form of a large, single stone or as multiple small stones like sand or gravel.
Why are they a problem?
The stones may cause an obstruction to the outflow of urine making your pet strain without passing urine. They can also cause trauma to the lining of the bladder or urethra resulting in production of bloody urine.
When there is an obstruction the bladder cannot empty and this is very painful. Pets may cry in pain, especially if their abdomen is pressed. They may also lick at their vulva or penis.
How do they form?
There are many causes of bladder stone formation and most cases are a combination of these. High concentrations of minerals in the urine can cause the small mineral particles to collect together and form stones. The increased levels of these minerals may be due to a diet rich in them or previous bladder injuries (like infection). Abnormalities in body metabolism can also cause increased mineral levels in the urine.
How are they diagnosed?
Some bladder stones can be palpated (felt) through the abdominal wall however not all are found this way. Most bladder stones are visible on x-ray or ultrasound. Stones not visible this way may require a contrast dye to be placed in the bladder before taking a radiograph (x-ray). Ultrasound examination is a very sensitive way to visualize both large bladder stones and the sand/gravel (small stones) that can also form. Cystitis (bladder infection) will cause similar signs to urinary calculi and is much more common, tests may need to be run to distinguish between cystitis and stones.
How are they treated?
There are two ways to remove bladder stones/calculi. The fastest is via surgery. The bladder is opened and the offending stones are removed. Surgery is indicated if there is an outflow obstruction from the bladder or infection associated with the stones or with some specific kinds of stone.
The other way to treat bladder calculi is via a prescription diet. There are three main disadvantages to this method.
- It is not effective on all types of stones. You may have to try to identify the stone type before trying the diet.
- It is slow to work, so if your pet is in pain or discomfort it may not be the best option.
- Not all pets will eat the prescription diet and it must be fed as a sole food source or it will not work.
Can they be prevented?
Yes. If stones are removed surgically or if small ones are passed in the urine, they should be analysed. This will tell us if the use of a prescription diet will be helpful in preventing further stone formation. Regular urine tests will be required to monitor for any signs of recurrence. Antibiotics may need to be used intermittently to treat bacterial infections.