Ureteral Obstruction in Cats and Subcutaneous Ureteral Bypass
What is ureteral obstruction?
The kidneys produce urine, which travels to the bladder through narrow tubes called the ureters. In cats, ureters are extremely small (often less than 0.4 mm in diameter), making them prone to becoming blocked. Ureteral obstruction prevents urine from leaving the kidney, resulting in a pressure buildup and leading to kidney damage. If left untreated, this damage may become permanent and can be life-threatening, particularly if both kidneys are affected or if the other kidney is not functioning normally.
What causes ureteral obstruction?
Ureteral stones (ureteroliths)
This is a common cause of ureteral obstruction. Nearly all feline ureteroliths are composed of calcium oxalate. They present a clinical challenge because multiple stones are usually present, 85% of cats will have stones in the kidneys (nephroliths) concurrently, and typically are NOT amenable to dissolution (dissolving through medical management).
Narrowing of the ureter (stricture)
Previous damage to the ureters such as inflammation, infection, blood clots as may be caused by previously dislodged stones can result in scar tissue formation, which can result in stricture and narrowing the ureter, thereby restricting urine flow.
Cancer
Benign or malignant tumours may compress the ureter externally or may originate from within the wall of the ureter itself. Either type may leading to partial or complete obstruction.
Who manages cats with ureteral obstruction?
Ureteral obstruction is a time-critical condition because the longer the ureter remains obstructed, the more likely is the development of irreversible kidney injury. Many cats affected by ureteral obstruction ALSO have a degree of underlying chronic kidney disease concurrently. Unfortunately, medical management alone is successful in only a small proportion of cases of ureteral obstruction. For these reasons, managing ureteral obstruction becomes a concerted effort between medicine and surgery departments.
Goals of treatment
Restore urine flow from the kidney to the bladder whilst preserving as much kidney function as possible, prevent further deterioration of kidney function, and relieve pain to improve quality of life.
Why is surgery recommended?
The premise of surgical management is to maintain urine flow from kidney to bladder whilst diverting urine away from the diseased/blocked ureter. This is typically performed using a Subcutaneous Ureteral Bypass (SUB) device.
What is a Subcutaneous Ureteral Bypass (SUB)?
A SUB is an artificial bypass system that allows urine to flow around the blocked ureter.
The system consists of three major components (see photo below):
- A silicone tube placed/secured into the kidney (Nephrostomy tube)
- A silicone tube placed/secured into the bladder (cystostomy tube)
- A small metal access port positioned beneath the skin
These components are connected to one another via the sampling port under the skin. Urine now flows directly from the kidney to the bladder through the SUB device.
The access port allows your veterinarian to flush the system periodically to ensure it continues to function properly and to sample the urine in a sterile manner when required.
Photograph illustrating components of a subcutaneous ureteral bypass (SUB) system. Source: www.norfolkvetproducts.com
Why choose a SUB instead of other procedures?
Historically, ureteral surgery carried a high complication rate in cats. Surgical techniques involving stenting (placing small tubes inside the ureter itself) or opening the ureter to remove the obstruction are usually not feasible in cats. This is due to the extremely small ureteral diameter (0.3-0.4 mm).
A SUB offers less manipulation of the ureter, lower risk of urine leakage from the ureter and lower risk stricture formation leading to recurrent obstruction. Having the ability to monitor and maintain the device through regular flushing and sampling of urine has led to higher long-term success rates.
Unfortunately, not every cat is a candidate for a SUB device. A thorough discussion is required regarding the procedure, managing expectations and discussion whether a SUB is the most appropriate option for your cat. Some cats require bilateral SUB placement if both ureters are affected.
Before surgery
Prior to surgery your cat will require a thorough clinical workup with our medicine service, including blood tests and urine testing and culture, blood pressure measurement, abdominal ultrasound and/or CT scan, intravenous fluid therapy, stabilisation of kidney function and electrolyte abnormalities and pain relief. Some cats require several days of hospitalisation before surgery.
During surgery
Your cat will undergo a general anaesthetic and their abdominal cavity opened.
During surgery, specialised silicone tubes are placed into the affected kidney and the bladder. The catheters are connected to a subcutaneous access port. The system is tested to ensure urine flows normally. X-rays are usually taken before recovery to confirm correct placement (see x-rays below).
Radiographs showing a successfully placed Subcutaneous Ureteral Bypass (SUB) in a feline patient
What are the benefits of a SUB?
Successful SUB placement will restore urine flow from the affected kidney, preserve remaining kidney function, reduce pain and nausea associated with obstruction and hopefully increase both quality and length of life.
What are the risks of SUB placement?
Although kidney function often improves after surgery, kidneys that have already suffered irreversible damage may not return to normal. As with any major surgery, complications can occur, which may include anaesthetic complications, bleeding and infection in the short term. In the medium to long term, other complications may include device blockage, leakage and movement, device mineralisation and persistent kidney dysfunction.
Caring for your cat at home
Most cats recover surprisingly well at home. You may notice mild, transient tiredness with temporary reduction in appetite. Activity should be restricted for approximately two weeks after surgery.
Lifelong SUB maintenance and patient monitoring
SUBs are NOT “place and forget” devices and will require lifelong maintenance to minimise the risk of device blockage or failure. Long-term management and patient monitoring typically occurs through an internal medicine specialist.
The access port (placed beneath the skin) allows for flushing of the device using sterile technique. The exact schedule varies depending on your cat. A typical flushing schedule occurs:
- Approximately 1 month after surgery
- Every 3 months initially
- Every 3–6 months thereafter
Regular flushing helps detect early blockage, prevent mineral build-up, confirms normal function and allows collect urine samples from the kidney if required.
Prognosis
Many cats experience an excellent improvement in comfort and quality of life following successful SUB placement. Overall outcome depends on several factors, including, how long the kidney has been obstructed, function of the opposite kidney, severity of chronic kidney disease, presence of infection, whether one or both ureters are affected, development of long-term complications.
Frequently Asked Questions
Will my cat be able to feel the SUB device?
No. The access port sits beneath the skin and is generally not bothersome once healing is complete.
Will the obstruction be removed?
Usually not. The SUB bypasses the obstruction rather than removing it. In some case the obstruction may resolve with time, or course through the ureter to the bladder
Can my cat live a normal life?
Many cats return to a very good quality of life after recovery and resume normal household activities.
Does the SUB need to be removed?
The device is designed to remain in place permanently unless complications require revision or replacement.
Will my cat still have kidney disease?
Many cats continue to have chronic kidney disease even after successful treatment. The SUB restores urine flow but cannot reverse permanent kidney damage.
Key Points
- Ureteral obstruction is an emergency that can permanently damage the kidney.
- A SUB device bypasses the obstruction and restores urine flow.
- Surgery aims to preserve kidney function and improve quality of life.
- Lifelong monitoring and regular flushing of the SUB device are essential.
- Most cats will have an excellent quality of life following successful surgery.
- Ongoing management of kidney disease is required.
Dr Fabian Trefny
BSc, BVSc, MANZCVS(SAS), MVetClinStud, DipECVS
If you have concerns for your pet in connection to this condition we recommend discussing it with your primary care vet in the first instance, or get in touch with our team for more information.
If you need urgent medical help, contact our 24 hour Pet Emergency team at Stafford, North Lakes, or Sunshine Coast on 1300 QLD VET (1300 753 838)