You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Occasionally stones (which are also called uroliths) form in the urinary bladder where they cause inflammation and discomfort - and sometimes they can block the urinary tract.

Urine does not simply consist of water, it contains many substances including minerals (eg calcium, magnesium and phosphorus), electrolytes (eg sodium and chloride), drugs and other waste products that the body needs to get rid of. 

Sometimes crystals can form in the urine and if these crystals aggregate together they can form a small stone. As time goes on these stones may get bigger and bigger, the eventual size that they reach depending upon several factors including the components of the stone, the amount of time that they remain in the urinary system and the concentration of the contents of the stone in the urine.

There are many factors involved in the formation of crystals including :

• Urinary tract infections ...these can occur before a stone forms and cause stones, or they can occur as a result of the damage caused by stones
• Diet - some components in foods (eg minerals) can predispose to stone formation if they are eaten in high concentrations
• Urine acidity ...some crystals form best in acidic or in alkaline urine

Pets that develop stones in their urinary bladder may show no signs at all, unless the wall of the bladder gets inflamed. That leads to increased frequency of urination and blood in the urine - in other words the typical signs of cystitis. 

If a stone moves from the bladder into the urethra it can sometimes block the tube - leading to straining and an inability to pass urine. This can be extremely serious because urine retention leads to back pressure up the urinary system, until it eventually affects the kidneys themselves. In addition, if the bladder becomes very distended the wall can sometimes rupture, leading to internal peritonitis. Male cats have quite a narrow urethra and they can get blocked by quite small stones or plugs of protein and mineral.

Very occasionally stones will form in the kidneys themselves where they can cause bleeding and obstruct urine outflow ...leading to kidney damage.

Treatment usually involves the surgical removal of the stones, but in some cases they can actually be dissolved in the bladder by changing the diet - without the need to perform surgery. If your pet has such a problem your veterinarian will advise on which method of treatment is most appropriate. Long term dietary management is sometimes needed to prevent recurrence.

Updated October 2013