If you or anyone you know has ever passed a kidney stone, you know how painful it is. If your cat starts passing a kidney stone or develops a stone or other obstruction in the tubes connecting the kidneys to the bladder (ureters), it can be excruciating for them, and although they can’t tell you what’s wrong, it’s obvious that something is not right.
Ureteral obstruction (not to be confused with urethral obstruction, which is much more common and often referred to as a “blocked cat”) has increased in frequency over the past couple of decades. What’s the difference? A ureteral obstruction stops the flow of urine from the kidneys to the bladder and can damage the kidneys. The more common urethral obstruction is a blockage of urine flow in the urethra, which connects the bladder to the external genitalia.
The general term for a stone that develops in the urinary tract is “urolith.” Kidney stones (nephroliths) and bladder stones (cystic calculi) are well-known entities, but uroliths can also form in the ureters.
The ureters in cats are so tiny that any stone formation can cause blockage to urine flow. In addition to stones that form in the ureter, kidney stones that try to pass often get stuck in the ureter, resulting in obstruction of urine flow. Other less common causes of ureteral obstruction include strictures (abnormal narrowing of the ureter), dried solidified blood and/or inflammatory cells, ureteral tumors, and accidental ligation (tying off) of the ureter during abdominal surgery.
An Obstruction Is an Emergency
Ureteral obstruction in cats is a medical emergency. Not only is it agonizingly painful for a cat, but if the obstruction is not relieved quickly enough, the kidney may become irreparably damaged, resulting in acute renal failure or worsening of already present chronic renal disease. The goal of therapy is to get urine flowing as quickly as possible. In some cases, medical therapy consisting of intravenous fluids, pain control, and the use of drugs that relax the ureter may relieve the obstruction. If medical therapy is not successful relatively quickly, though, surgical intervention is usually indicated.
“There is likely no better surgical option available for cats who have a ureteral obstruction (e.g., stone, stricture, kinking) than the subcutaneous ureteral bypass (SUB) procedure,” says Dr. Daniel Lopez, assistant professor in section of Small Animal Surgery at the Cornell University College of Veterinary Medicine.
“The historical ureterostomies (procedure where an incision is made into the ureter to remove the stone) and stents (tube placed inside the ureter to reestablish urine flow) were difficult to perform and had very high complication rates. In my opinion, the SUB, while definitely an advanced procedure, is probably easier to perform than the aforementioned procedures and has a lower complication rate.” Dr. Lopez says Cornell performs about five feline SUB procedures per year.
What Is a SUB?
With the cat under general anesthesia, an incision is made into the abdomen to access the kidneys. With the help of fluoroscopy (real-time, continuous X-ray imaging) a catheter is placed into the center of the kidney where urine is produced. The catheter is then passed through the body wall, so it travels outside the abdomen but under the skin, where it is attached to an accessible subcutaneous port that is similar to those used in humans undergoing chemotherapy.
A second catheter is attached to the port, and the other end is inserted into the bladder, thereby creating an effective alternate route for urine flow from the kidney to the bladder. The port is used for routine flushing of the system to keep it clear and functioning, and the system requires intensive monitoring and maintenance for the rest of the cat’s life.
“Unfortunately, there still exists a fair complication rate with the SUB procedure,” says Dr. Lopez. “The biggest complications we see are complications at the time of placement (e.g., kinking/not flowing properly, blood clots, leakage), mineralization of the SUB unit over time (urine stops flowing through it), infection, and lack of improvement of the underlying kidney injury (aka they have chronic kidney disease).”
The other issue that must be considered when deciding whether to pursue SUB or not is the expense. It is not only the cost of the procedure you must be aware of, but the continued cost associated with maintenance of the system as well.
“SUBS are not a ‘one-stop shop’ procedure,” says Dr. Lopez. “They require intensive long-term management that can be cost prohibitive. While a SUB at Cornell may cost $7,000 to $9,000, we must warn owners that they can expect to spend thousands of dollars in follow-up care over the life of the animal. This includes rechecks every other week for the first few months, and then at least every three to six months for life.”
“At these visits, we flush the systems to try to limit mineralization and maintain patency and obtain samples for culture looking for infection. All of this adds up to significant financial and time investment that may not be possible for many owners. Each of these visits might cost around $500. And then if the SUB mineralizes or becomes infected, we often have to replace the entire system, which is then another $7,000 to $9,000 in cost,” says Dr. Lopez.
Obviously, this is a big decision. Long-term prognosis is also a consideration, as Dr. Lopez says that most of these cats already have some degree of renal dysfunction.
Why Not Use Medical Therapy?
The problem with medical therapy for this condition is that establishing urine flow ASAP is critical to a good outcome, and the veterinary literature suggests a very low success rate with medical treatment of ureteral blockages.
While prescription diets are known to successfully dissolve struvite bladder stones in cats, most ureteral stones in cats are calcium oxalate stones, which are not amenable to dietary dissolution. Dissolution diets can also take weeks to months to work, and in many cases of ureteral obstruction, waiting this long results in poor outcomes.
What Should You Do?
If your cat is diagnosed with a ureteral blockage, consult carefully with your veterinarian. If you decide the SUB procedure is right for you and your cat, it can give your cat the chance for a better prognosis and quality of life.
“The really cool thing is that we’ve seen cats live beyond two to three years, depending on subsequent stage of kidney disease,” says Dr. Lopez. “As such, the procedure is really beneficial, it is just really intensive.”
