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

Among the emergency conditions we encounter in our daily practice, feline ureteral obstruction is one of the most serious. The ureters are tubes that transport urine from the kidneys to the bladder. If these tubes become blocked, typically by stones, it results in ureteral obstruction.

Compared to bladder stones, which form within the bladder, ureteral obstruction is a much more urgent condition. A delay of even one day in diagnosis can lead to acute kidney failure or uremia, often proving fatal.

Based on my clinical experience, this article will detail the critical early signs of feline ureteral obstruction that should 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

Ureteral obstruction is often caused by calcium oxalate stones

The most common cause of ureteral obstruction is stones formed in the kidneys flowing into and getting lodged in the ureter. Other causes include blood components from kidney bleeding.

While there are several types of feline urinary stones, those that block the ureter are very frequently calcium oxalate stones, which cannot be dissolved through dietary management. 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 feline urinary stones. However, acidic urine can conversely promote the formation of calcium oxalate crystals, which is why calcium oxalate stones have become more prevalent in ureteral obstructions.

Research on the treatment of ureteral stones indicates that dietary or medical management is effective in only about 10% of cases, highlighting that most ureteral obstructions require surgical intervention.

Why is obstruction dangerous?

A cat's ureter is only about 0.4 mm in diameter, comparable to a mechanical pencil lead, indicating its extreme narrowness. When a stone obstructs the ureter, urine cannot flow from the kidney to the bladder and backs up into the kidney, causing it to swell significantly (hydronephrosis). In hydronephrosis, the urine-producing structures are severely compressed, leading to a drastic decline in kidney function (acute kidney injury). As a result, the body cannot excrete metabolic waste products (toxins), quickly progressing to uremia. Acute kidney injury and uremia are extremely dangerous and life-threatening without immediate intervention.

[From a Veterinarian's Clinical Experience] Signs of Urination Problems May Not Always Be Present! Dangerous Signs of Ureteral Obstruction

Changes in urine color/volume, frequent trips to the litter box

In cases of ureteral obstruction, urine may be produced but not reach the bladder, leading to abnormally reduced urine volume or frequent trips to the litter box with no urination. If the ureter is bleeding due to a stone, blood may appear in the urine. Since there are two ureters (one on each side), if only one is obstructed, urine may still be passed normally. Therefore, it is common for ureteral obstruction to occur even without noticeable changes in urination or litter box frequency. In such cases, ureteral obstruction can only be diagnosed through imaging.

Sudden "vomiting" and "lethargy and hiding"

In cases of ureteral obstruction, acute kidney injury can rapidly progress to uremia. When this occurs, the cat is overwhelmed by severe nausea due to uremic toxins, leading to repeated vomiting of stomach fluid or foam. I believe it is far more common for owners to bring their cats in with complaints of "repeated vomiting and lethargy" than to notice abnormal urination.

While observing, thinking it might just be a hairball, the cat might become lethargic and hide in a corner of the room or under the bed. Since the kidneys swell with urine, abdominal pain can also occur. Cats often hide pain, so they might be lethargic and secluded in unusual places. If symptoms have progressed to this extent, rush to an emergency veterinary clinic, even at night.

Don't assume "frequent trips to the litter box = constipation"!

A very common scenario in clinical practice is owners saying, "My cat is straining repeatedly in the litter box. They get angry when I touch their abdomen, so I thought it was severe constipation." Upon examination, we often find the kidneys are significantly enlarged, but the bladder is of normal size, and there is no accumulation of feces.

However, ultrasound or X-ray examinations frequently reveal an obstructed ureter and enlarged kidneys, or stones on the X-ray. Remember, "frequent trips to the litter box" isn't always constipation; it can be an emergency in the urinary system that is life-threatening.

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

Rapid diagnosis with ultrasound can be life-saving

At the hospital, while blood tests confirm abnormal kidney values (BUN and creatinine), an ultrasound (echo) examination is immediately used to determine if the "kidney is swollen" and "where in the ureter the stone is located."

Risks and limitations of medical treatment

While medical treatment may improve the condition, as mentioned earlier, it is only effective in about 10% of cases. Medical treatment is considered when the ureteral obstruction is incomplete and urine flow is maintained, when kidney dilation is mild, or when kidney function and overall condition are stable. In such cases, intravenous fluids may be administered, and the patient may be observed for a short period. During this time, the obstruction is evaluated, and the treatment plan is determined. However, medical treatment cannot completely resolve the obstruction and may even worsen the condition.

Types of Ureteral Obstruction Treatment and the Latest Treatment: "SUB System Implantation"

Most treatments for ureteral obstruction are surgical. Surgical options for ureteral obstruction include "ureterotomy," "neoureterocystostomy," "ureteral stent placement," and "SUB (subcutaneous ureteral bypass) system implantation."

Ureterotomy involves incising the ureter to remove stones. Neoureterocystostomy involves excising the narrowed ureter and reattaching it to the bladder. Ureteral stent placement is a procedure where a tube called a stent is inserted into the ureter to widen it.

The latest treatment developed is the SUB system implantation. This procedure connects the kidney and bladder with a tube, bypassing the obstructed urinary tract to allow urine flow. Traditional treatments could lead to postoperative narrowing of the ureter (stricture), urinary tract infections, or displacement of the implanted stent. SUB system implantation allows for urine flow even with severe or multiple ureteral obstructions. Furthermore, since it bypasses the ureter, the risk of re-obstruction is eliminated, allowing for long-term management. This has saved many lives. However, regular flushing of the tube is necessary to prevent obstruction, requiring lifelong care.

Additionally, not all veterinarians are able to perform SUB system implantation. It requires experience and training, so most SUB system surgeries are performed at well-equipped animal hospitals. I myself do not perform SUB system implantation and refer these cases to secondary hospitals. If immediate surgery is not possible, a "nephrostomy tube" may be inserted into the kidney through the skin to temporarily drain urine externally, managing the patient until surgery at a secondary hospital.

Even if urine flow to the bladder is restored through surgery, the damaged kidney will not fully recover. To maintain the remaining kidney function, dietary changes to therapeutic food and subcutaneous fluid therapy may be necessary.

What Owners Can Do to Prevent Ureteral Stones

"Hydration" is paramount

The most important preventative measure against stone formation is to dilute the urine. It's crucial to find ways for your cat to naturally increase their water intake, such as placing multiple water bowls around the house, offering "lukewarm" water that cats prefer, or incorporating wet food into their diet.

Additionally, over-the-counter lower urinary tract health foods that are not prescription diets are often formulated to acidify urine to combat struvite. This is believed to contribute to the increase in calcium oxalate stones. If your cat does not have stones, it may not be necessary to use lower urinary tract health food.

Routine litter box checks

When cleaning the litter box, check the size and number of urine clumps (in cat litter) daily. Noticing subtle changes, such as "clumps being smaller than usual" or "more frequent trips to the litter box," can lead to early detection of illness.

Summary: Feline "Ureteral Obstruction" is a Race Against Time! Seek Veterinary Attention Immediately if You Notice Any Abnormalities

Feline ureteral obstruction is an extremely dangerous emergency condition where deciding to "wait until tomorrow" can be fatal. In clinical practice, we frequently see cases where owners come in saying, "I thought it was just constipation," "I thought it was just vomiting," or "I thought my cat was urinating, so it couldn't be a urinary problem." By the time they arrive, acute kidney injury has often already progressed, and the cat is in a critical state.

If your cat exhibits symptoms such as "making urination gestures but nothing comes out," "vomiting," or "lethargy," seek veterinary attention as soon as possible.

Daily litter box cleaning is an opportunity to check for "mail" from your beloved cat (a barometer of their health). Monitor their urine volume and frequency regularly, and never overlook your cat's small cries for help.

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