Besides the bladder, urinary stones in pets are also found in the kidneys and the urinary tracts (tubes), where they can be lodged and block the urine flow. Kidney stones are more common in cats than in dogs. Dogs of small breeds are more represented and some breeds are genetically predisposed to have the problem (Dalmatians, English, Yorkshire terriers and Schnauzers). Ferrets, rabbits and reptiles also have urinary stones and blockage.
Kidney stones can be of different size, type and structure. One or more kidney stones may be found in one or both kidneys. The size and number of stones usually determine the amount of damage to the kidneys and the signs exhibited by the affected pets.
Many pets with few stones are asymptomatic and are accidentally diagnosed (x-ray or Ultrasounds). Others show signs of abdominal pain, bloody or pussy urine, frequent urination, vomiting, not eating and depression. Affected kidneys may develop secondary infections and severe damage leading to renal failure.
When kidney stones are small enough, they may travel within the urinary tracts (uretere and urethra) and cause obstruction. Males are more likely to have a urethral blockage due to their long urethras and narrowing of urethral segments. In cats the obstruction is generally caused by numerous sand-like stones and sludge, while in dogs it is generally caused by a single larger stone (calculus). Urinary obstruction is very painful and dangerous. It is a medical emergency that requires immediate intervention. Affected animals vocalize in pain, have arched backs and tense abdomens and attempt to urinate continuously. Urine may dribble from the urethra and contain blood.
Asymptomatic animals with one or two small stones may not need any treatment and conduct a normal lifestyle. Young and symptomatic animals can be treated surgically (stone removal) and medically (antibiotics and other appropriate medications). Some veterinary schools offer lithotripsy, which is blasting the stones from the outside using electric shock wave or laser. This procedure works best on small stones in the kidneys or urinary tracts. Both kidney surgery and lithotripsy cause damage to the kidneys. Urethral stones may be flushed back into the bladder and then removed surgically via cystotomy (opening and cleaning of the bladder). Many times the bladder will have additional stones and will need to be opened anyway. Another procedure is hydropropulsion, where the stones are manipulated with water under pressure. When these procedures fail, the urethra has to be incised and left open to allow urination. There are several procedures that can be used in dogs and cats, depending on the specific situation.
X-rays or ultrasounds are indicated in any case of urinary stones in order to evaluate the degree and extension of the problem (location, number, size and shape of the stones). The stones should be analyzed for complete diagnosis and appropriate treatment. In some cases medical management can be used to dissolve or prevent the stones.