Older cats frequently develop stones in their kidneys (nephroliths). Chronic kidney disease increases the chances of these kidney stones forming. Thirty percent of cats with kidney disease develop kidney stones. Ninety-eight percent of these stones are made of calcium and will not dissolve with diet.
Kidney stones that do not block the opening of the ureter (the tube that passes urine from the kidney to the bladder) or cause pain usually do not require surgical removal. Instead, the stones are monitored with x-rays and/or abdominal ultrasound at least yearly to determine if they are starting to block the ureter. These nephroliths also may become infected with bacteria. Bacteria can spread from the stones to the rest of the urinary tract and cause infection. Consequently, your cat’s urine needs to be cultured one to two times a year when stones are present. If an infection develops, then antibiotics are usually needed for six to eight weeks or longer.
Lithotripsy (ultrasound shock waves to break up stones) is not currently an option for feline kidney stones. Lithotripsy can be performed in large dogs as well as humans. Feline kidneys are too small for the lithotripsy machines currently available. The powerful soundwaves cause too much tissue damage in the small feline kidneys.
When stones are present, crystals are not usually found in the urine. The stones are diagnosed with x-ray or ultrasound. Sometimes kidney stones migrate into the ureter. Small stones may pass all the way into the bladder. Larger ureteral stones (ureteroliths) can become stuck in the ureter. If they completely obstruct the ureter, then urine cannot pass into the bladder and backs up into the kidney. This damages the kidneys and can eventually cause it to be a dilated, nonfunctional, urine-filled “sack”. Once ureteral stones become lodged in the ureter, the walls of the ureter start swelling and spasm around the stone. This makes the stone become even more firmly lodged in the ureter.
Sometimes the ureteral stones can be dislodged medically with IV fluids, pain medication and muscle relaxants. However, most of the time (80-90%) surgery is required.
Surgery for ureteral stone removal takes several forms. Sometimes the stone can be removed from the ureter directly using microsurgery. More frequently, the ureter has to be transected above the blockage and the end of the ureter re-implanted into the bladder. If the blockage is too far away from the bladder for this to occur, then the kidney needs to be removed or ureteral stents need to be placed. Left untreated, the affected kidney will be both painful and nonfunctional if not removed. It also will serve as a bacterial source for infections. If the other kidney is healthy enough then surgical removal of the bad kidney is possible. This can be done at our hospital and costs approximately $2,000-2,500.
When the affected kidney still has function, ureteral stents can be placed. These tiny tubes snake through the ureter past the stones and create a functional passage for urine to pass from the kidney into the bladder. These stents may be left in place long-term. They can be placed surgically or sometimes through the bladder using a cystoscope in female cats.
Currently the closest locations that are able to place ureteral stents are Michigan State University College of Veterinary Medicine in East Lansing and Purdue University in northern Indiana. Cost is approximately $2,000-4,000.
Overall, many cats with kidney stones do very well and the stones do not cause clinical problems. Stones that become extremely large or obstruct the ureter do require surgical removal. Please call us if you have any questions or to schedule your cat’s follow up examination.