The bladder collects urine from the kidneys and contracts to expel its contents during urination via a tube called the urethra. The terminal part of the urethra in a male dog runs through a bone called the os penis. This part of the urethra is relatively narrow and can prevent passage of bladder stones.
How do stones form?
There are many causes of bladder stones. Calcium oxalate stones are most commonly found in male dogs and form due to a condition of the kidney that promotes oxalate secretion into the urine. Certain breeds, such as schnauzers, are more prone to have this problem. Oxalate stones may form if the pet has a tumor of the parathyroid gland or certain types of cancer.
Struvite stones may be due to chronic bacterial bladder infection. Some types of bacteria breakdown urea in the urine to form ammonium, an ingredient of struvite stones.
Ammonium biurate stones form if a pet has a liver disease such as a portosystemic shunt. In such cases the liver is unable to clear the blood of uric acid, thus stones form. Surgical correction of the shunt usually prevents the stones from recurring.
Some dalmatians lack an enzyme called uricase in their liver and kidney cells that results in the accumulation of high levels of uric acid in the blood, which causes the formation of urate stones in the kidneys and bladder.
If the stones are causing incomplete obstruction of the urethra, the pet will dribble urine or have a poor stream of urine during urination. If the urethra is completely obstructed by a stone, the affected dog will attempt to urinate without success. As the bladder becomes more and more distended, signs of pain may become evident. These include, whining/whimpering, panting, pacing and pulling the lips back (grimace). Upon palpation of the abdomen, the bladder will be painful, firm and enlarged. As the toxins accumulate in the blood, the patient develops signs of vomiting, abnormal heartbeats, depression and in severe cases, coma and death.
X-rays of the abdomen are necessary to show that the obstruction is caused by stones in the urethra and bladder. X-ray of the urethra and bladder following injection of contrast may also be used to identify the cause. Blood is tested to evaluate for impaired kidney function. Abdominal ultrasound can also be used to evaluate the urinary tract but may not be necessary in every patient
Urinary blockage is an emergency; therefore, it is essential to have this condition treated immediately. Your veterinarian will start intravenous fluid therapy, as these patients commonly are dehydrated. If the potassium level is very high, glucose (a type of sugar) and insulin are administered intravenously to lower the level of this electrolyte. In most cases, the patient will need to be anesthetized in order to flush the stones from the urethra into the bladder. A urinary catheter is then passed up the urethra and into the bladder. Stones are surgically removed from the bladder once the patient is stable and the toxins have been eliminated from the blood stream, which typically is within 24 hours.
If the stones cannot be flushed back into the bladder, an emergency scrotal urethrostomy is recommended. This procedure requires castration to be performed if the pet is intact, as this is the location where the urethra will be surgically opened. A one-inch incision is made into the urethra and the lining of urethra is sutured to the skin edges to create a permanent opening through which urine can pass. If the stones lodged in the os penis cannot be removed, they can be safely left in place. If the stones remaining in the bladder are too large to be removed by a nonsurgical flushing technique, a cystotomy is performed to remove the stones.
For more information on this subject, speak to the veterinarian who is treating your pet.