[Written by a Veterinarian] Feline Ureteral Obstruction: A Race Against Time! Dangerous Symptoms and Latest Treatments from the Clinic

One of the emergency conditions we treat with the greatest urgency in our daily practice is "ureteral obstruction" in cats. The ureter is the tube that carries urine from the kidneys to the bladder, and if it becomes blocked by a stone or similar object, it results in ureteral obstruction.

Compared to bladder stones that form inside the bladder, ureteral obstruction is highly urgent; a delay in detection of even one day can lead to acute renal failure or uremia, often becoming a life-threatening situation.

In this article, based on my personal experience in the clinical setting, I will explain in detail the early symptoms of feline ureteral obstruction that must not be overlooked, as well as the latest life-saving treatments (such as the SUB system).

Causes of Feline "Ureteral Obstruction" and the Mechanism of Stone Blockage

"Calcium Oxalate Stones" Frequently Block the Ureter

The most common cause of ureteral obstruction is a "stone" formed in the kidney that enters the ureter and becomes lodged along the way. In other cases, obstruction can occur due to blood components resulting from bleeding in the kidney.

There are several types of stones in cats, but those that obstruct the ureter are most frequently "calcium oxalate stones," which cannot be dissolved through dietary therapy. The reason for this is that some cat foods currently on the market are designed to keep urine pH acidic to dissolve struvite, a common cause of stones in cats. Because acidifying the urine makes it easier for calcium oxalate crystals to form, it is believed that calcium oxalate stones have become the primary cause of ureteral stones.

Research results on the treatment of ureteral stones indicate that improvement through diet or medical therapy is only about 10%, showing that most cases of ureteral obstruction require surgical intervention.

Why is a blockage dangerous?

A cat's ureter is only about 0.4 mm wide; you can imagine how thin that is by picturing the lead of a mechanical pencil. When a stone blocks the ureter, urine cannot flow from the kidney to the bladder and instead backs up into the kidney, causing it to swell severely (hydronephrosis). In a state of hydronephrosis, the part of the kidney that produces urine is significantly compressed, leading to a drastic decline in renal function (acute kidney injury). Consequently, the body cannot excrete waste products (toxins), and the condition progresses to uremia in a short period. Acute kidney injury and uremia are extremely dangerous and can be life-threatening without emergency treatment.

[From Veterinary Clinical Experience] No Signs of Urination! Dangerous Signs of Ureteral Obstruction

Urine Color/Volume Changes and Frequent Trips to the Litter Box

In cases of ureteral obstruction, although urine may still be produced, it is not transported to the bladder, which can result in an abnormal decrease in urine volume or repeated trips to the litter box with no urine produced. Additionally, if the ureter is bleeding due to a stone, blood may appear in the urine. Because there is a ureter on each side, if only one side is obstructed, urine may still pass normally, so we often see cases of ureteral obstruction where there are no obvious changes in urination habits or litter box frequency. In these cases, ureteral obstruction cannot be diagnosed without diagnostic imaging.

Sudden "Vomiting" and "Lethargy/Hiding"

Ureteral obstruction rapidly leads to acute kidney injury and eventually a state of uremia. In this state, the cat suffers from intense nausea caused by uremic toxins, leading to repeated vomiting of stomach acid or foam. I find that it is overwhelmingly more common for owners to come in complaining that their cat is "vomiting repeatedly and acting lethargic" rather than noticing abnormalities in urination.

While the owner waits to see if it’s "just a hairball," the cat will hide in a corner or under a bed, lethargic and immobile. Because the kidneys become enlarged with urine, the cat may experience abdominal pain. Cats often hide their pain, so they might be found lethargic in an unusual place. If symptoms have progressed to this stage, please rush to an emergency veterinary hospital, even at night.

Don't assume "Frequent litter box visits = Constipation"!

A very common scenario in the clinic is: "My cat keeps straining in the litter box. It gets angry when I touch its belly, so I thought it had severe constipation." During the clinical examination, I often find that the kidneys are enlarged to the touch while the bladder is of normal size—and, of course, there is no impacted stool.

However, ultrasound or X-ray examinations often reveal an obstructed ureter with enlarged kidneys, or stones detected on the X-ray. Please do not assume that "frequent trips to the litter box" means constipation; remember that it could be a life-threatening urological emergency.

From Diagnosis to Surgery: The Life-Saving "SUB System" and the Limits of Medical Therapy

Rapid Ultrasound Diagnosis Can Save a Life

At the hospital, we verify abnormalities in kidney values (BUN and creatinine) through blood tests while simultaneously using ultrasound to instantaneously determine if the kidneys are swollen and where the stone is located in the ureter.

The Risks and Limits of Medical Therapy

While there is a possibility of improvement through medical therapy, as mentioned, this only occurs in about 10% of cases. Medical therapy is indicated when the ureteral obstruction is incomplete and urine flow is maintained, or if the kidney dilation is mild and the kidney function and general condition are stable; in such cases, we may provide IV fluids and monitor the patient for a short period. During this time, we evaluate the site of the obstruction and determine the course of treatment. However, medical therapy cannot resolve a complete obstruction and may even lead to further deterioration.

Types of Ureteral Obstruction Treatment and the Latest Method: "SUB (Subcutaneous Ureteral Bypass) System Placement"

The majority of treatments for ureteral obstruction are surgical. Surgical options considered for ureteral obstruction include ureterotomy, ureteroneocystostomy, ureteral stent placement, and SUB system (subcutaneous ureteral bypass) placement.

A ureterotomy involves cutting the ureter to remove stones. A ureteroneocystostomy involves removing the narrowed section of the ureter and reconnecting it to the bladder. Ureteral stent placement is a procedure where a tube called a stent is inserted into the ureter to dilate it.

The latest treatment developed is SUB system placement. This involves connecting the kidney to the bladder with a tube to bypass the obstructed urinary tract and allow urine to flow. Traditional treatment methods sometimes resulted in complications such as post-surgical narrowing of the ureter (stricture), urinary tract infections, or the stent shifting out of place. The SUB system allows for urine drainage even when the ureteral obstruction is severe or if there are multiple blockage points. Furthermore, because it does not rely on the ureter itself, the risk of re-obstruction is eliminated, allowing for long-term management. This has saved many lives. However, because the tube requires periodic flushing to prevent blockages, it necessitates lifelong care.

Also, not all veterinarians can perform the placement of this SUB system. As it requires experience and training, most surgeries are performed at animal hospitals equipped with the necessary facilities. I do not personally perform SUB system placements, and I refer such cases to secondary hospitals. If surgery cannot be performed immediately, we may insert a "nephrostomy tube" through the skin into the kidney to temporarily drain urine out of the body while managing the patient until the surgery at a secondary hospital.

Even after urine flow to the bladder is restored through surgery, a kidney that has been damaged once will not recover. Changes to a therapeutic diet and follow-up appointments for subcutaneous fluid therapy may be necessary to maintain remaining kidney function.

What Owners Can Do to Prevent Ureteral Stones

Most Importantly: "Hydration"

The best prevention method for stones is to dilute the concentration of the urine. It is important to find ways to encourage your cat to drink more water naturally, such as setting up multiple water stations around the house, using "lukewarm water" which many cats prefer, or incorporating wet food into their diet.

Additionally, non-prescription foods designed for lower urinary tract health are made to keep urine pH acidic to combat struvite. It is believed that this contributes to the increase in calcium oxalate stones. If your cat does not have stones, there is likely no need to intentionally feed them food for lower urinary tract health.

Make Litter Box Checks a Habit

When cleaning the litter box, please check the "size and number of urine clumps (in the litter)" every day. Noticing even subtle changes, such as "the clumps are smaller than usual" or "the frequency of visits has increased," can lead to the early detection of disease.

Summary: Feline "Ureteral Obstruction" is a Race Against Time! Seek Medical Attention Immediately if You Sense Anything Wrong

Feline ureteral obstruction is an extremely terrifying emergency where the decision to "wait and see until tomorrow" can be fatal. In the clinic, we often see cases where owners arrive saying, "I thought it was constipation," "I thought it was just vomiting," or "My cat was still urinating, so I didn't think it was a urinary disease." By the time they arrive, acute kidney injury has often already progressed, and the cat is in a dangerous state.

If you see symptoms like "posturing to urinate but nothing comes out," "vomiting," or "lethargy," please take your cat to an animal hospital as soon as possible.

Daily litter box cleaning is a way to check for messages (barometers of health) from your beloved cat. Stay aware of your cat's usual urination volume and frequency so you never miss these small SOS signals.

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