Ureteral Obstruction is defined as a blockage in one or both of the ureters, the tiny, spaghetti-thin tubes that carry urine from the kidney down to the bladder. In the context of feline kidney disease, this is one of the most critical and life-threatening emergencies a cat owner can face.
The Anatomy of the Problem The feline ureter is incredibly small, with a diameter of only about 0.4 millimeters. Because the lumen (the hollow inside) is so narrow, it does not take a large object to create a total dam. The most common cause is a Ureterolith (a kidney stone moving out of the kidney), specifically Calcium Oxalate stones. Other causes can include dried blood clots, strictures (scar tissue narrowing the tube), or tumors pressing from the outside.
"Big Kidney, Little Kidney" Syndrome When a stone becomes lodged in the ureter, urine production does not stop; it simply has nowhere to go. The urine backs up into the kidney, causing the organ to swell massively with fluid, a condition called Hydronephrosis. The pressure inside the kidney skyrockets, crushing the delicate filtration tissue and causing rapid cell death.
-
The "Big" Kidney: The blocked kidney swells and becomes painful.
-
The "Little" Kidney: The opposite kidney is often small, scarred, and shrunken due to pre-existing chronic disease (CKD). This creates a disastrous scenario: the "good" (larger) kidney is blocked and useless, while the "bad" (small) kidney cannot support the cat alone. The result is a sudden, severe spike in toxins (Post-renal Azotemia) and acute failure.
Why "Passing the Stone" Rarely Works In humans or dogs, doctors often use fluids and muscle relaxers to help the patient "pass the stone." In cats, this success rate is dismally low (less than 10-15%) because the ureter is too small and prone to spasming tight around the stone. Waiting for a cat to pass a stone is often a waiting game that ends in the death of the kidney.
The Solution: The SUB System Because traditional surgery to cut into the tiny ureter often results in scar tissue that blocks the tube again (stricture), veterinary surgeons rarely stitch the ureter anymore. The modern gold standard for treatment is the Subcutaneous Ureteral Bypass (SUB).
-
Surgeons place a new, artificial tube that connects the kidney directly to the bladder, completely bypassing the blocked natural ureter.
-
This device remains inside the cat permanently and has a small port under the skin that allows vets to flush and clean the tube during check-ups. It essentially gives the kidney a new "drain," instantly relieving the pressure and saving the organ.
Disclaimer: This content is for educational purposes only and does not constitute veterinary medical advice. Always consult with your primary care veterinarian or a veterinary internal medicine specialist regarding your cat’s specific condition.