The names primarily describe enlarged structures, rather than the same disease stage in every cat. The finding alone does not establish permanent kidney failure. However, possible obstruction must be investigated promptly, because even a partial restriction of flow can damage a kidney.
When to see a vet urgently
Contact your vet immediately if your cat develops any of the following:
- sudden loss of appetite, vomiting and marked weakness;
- severe abdominal or flank pain, or rapidly deteriorating health;
- failure to pass urine normally or straining without producing any;
- known kidney disease with a sudden change in general condition.
Continuing to urinate does not rule out a blocked ureter. You can find a vet near you.
Overview
Normally, urine flows freely from the kidneys to the bladder through the ureters. With an obstruction, pressure rises and the ureter gradually dilates. A prolonged restriction damages kidney tissue and reduces its filtering ability. The condition is often symptom-free and discovered on ultrasound only at a late stage.
The ureter carries urine from a kidney to the bladder. The urethra is a different structure: it carries urine from the bladder out of the body. With a blocked ureter, the bladder may therefore empty normally even while one kidney is at risk. An apparently normal toilet visit does not show that urine from both kidneys is flowing freely.
Mild renal pelvis dilation can also occur without obstruction, for example with increased urine production, chronic kidney disease or infection. Conversely, a genuine blockage does not always cause marked enlargement. Ultrasound findings are therefore considered alongside symptoms, other imaging findings and trends in kidney values.
Causes
- urinary stone disease, with stones in the ureter, known as ureterolithiasis;
- tumours of the bladder, urethra or neighbouring organs;
- ureteral narrowing after inflammation or injury;
- congenital developmental abnormalities;
- compression of the ureter from outside, for example by a tumour.
A stone in the ureter, narrowing of its wall and external compression obstruct flow in different ways. A blood clot or inflammatory material can also block the channel. The significance of bladder or urethral disease depends on where the obstruction lies and whether it affects the ureteral openings or overall urine outflow.
Other possible obstructions are investigated if imaging shows no clear ureteral stone. Narrowing may also occur alongside a stone. Simply calling the finding urinary stone disease does not always describe every change affecting treatment.
Risk factors
- cats with urinary stone disease;
- middle-aged and older cats;
- chronic urinary tract inflammation;
- certain breeds with an inherited predisposition to urinary stones, including Persians and Birmans.
Stone type and the individual medical history matter more than breed when choosing treatment. Any cat can form calcium oxalate stones. Evidence is not equally strong for every listed factor as an independent risk for ureteral dilation specifically. Inflammation may be a cause, a concurrent finding or a consequence of stagnant urine.
Typical symptoms
- reduced appetite and lethargy;
- nausea and vomiting;
- tenderness in the lower back region;
- blood in the urine, known as haematuria;
- frequent or difficult urination;
- signs of chronic kidney failure, including large urine volumes, thirst and weight loss.
Frequent urination or visible blood may be entirely absent. Ureteral obstruction often causes vague symptoms such as reduced eating, hiding and nausea. If the other kidney functions well, blood creatinine may also remain normal. Do not therefore wait for obvious urination difficulty or abnormal blood values before seeking investigation.
If both ureters become blocked, or the other kidney is already damaged, health can deteriorate rapidly. Tell your vet about urination patterns, drinking and previous kidney results, even if they seem contradictory. You cannot determine the side or severity of an obstruction at home.
Complications and consequences
- chronic kidney disease (CKD);
- complete loss of function in the affected kidney;
- inflammation of the renal pelvis, or kidney infection;
- death without treatment when both sides are affected.
Consequences depend on the duration and severity of obstruction and the remaining kidney function. Some function may return after flow is restored, but existing tissue damage may be permanent. If infected, pus-containing material accumulates in an enlarged renal pelvis, particularly urgent assessment and treatment of both obstruction and infection are needed.
Diagnosis at the vet
- ultrasound of the kidneys and ureters to identify dilation, a stone or a tumour;
- X-rays to identify stones visible on radiographs;
- contrast imaging, or urography, to assess whether the ureter is open;
- urine testing for blood, protein, crystals and bacteria;
- blood biochemistry to assess raised creatinine and urea.
Ultrasound assesses both kidneys, the renal pelves and as much of the ureters as possible. It also looks for the point where a dilated ureter narrows, alongside stones, wall changes and surrounding structures. A single renal pelvis measurement is not enough to distinguish obstruction from other causes of dilation.
X-rays and ultrasound complement each other. However, a stone visible on an X-ray does not alone show whether it completely blocks flow. In unclear cases, contrast material can help assess ureteral patency. Pyelography follows contrast passing onwards from the renal pelvis. Your vet decides whether the investigation is needed and how it is performed.
As well as creatinine and urea, blood tests assess potassium and other electrolytes. A urine sample and, when needed, culture help investigate possible infection. The absence of bacteria in a lower urinary tract sample does not always rule out infection higher up. Imaging and laboratory findings are interpreted together.
Treatment and restoring urine flow
First, dehydration and dangerous electrolyte disturbances are corrected as needed, with treatment for pain and nausea. Fluid therapy is carefully supervised: giving large amounts of water at home does not remove a mechanical obstruction. If medical treatment is tried in a stable patient, kidney values, urine production and imaging findings are monitored closely. Deterioration requires a change of plan.
Calcium oxalate stones in cats cannot be dissolved with diet. Treatment of a diagnosed ureteral obstruction must therefore not be delayed while waiting for a new food to work. The approach depends on the location of the stone or other obstruction, ureteral structure and your cat's condition. Referral to a practice experienced in these procedures may be needed.
Options include a stent inside the ureter, a subcutaneous ureteral bypass (SUB) system or ureteral surgery. A stent supports urine flow within the ureter. A bypass system provides an alternative route around the obstruction. The appropriate method is not decided solely by the degree of dilation, and no single technique suits every case.
Procedures also carry risks. A support device can become blocked or move, and leakage or narrowing may occur after surgery. Some cats need another procedure later. Results from studies comparing methods depend on patient selection and operator experience, so they cannot guarantee an individual cat's outcome.
Antibiotics are chosen according to infection, ideally using culture and susceptibility testing. They do not replace relieving the obstruction. After flow returns, urine production may be higher than normal, requiring continued fluid and electrolyte monitoring. Discharge is assessed according to your cat's condition and the ongoing care needed.
Home care, monitoring and prognosis
At home, monitor appetite, weight trends, vomiting, activity and urination. Do not force food into the mouth. If eating is unsuccessful, contact the practice to plan nutritional support. Keep water easily accessible, but increased drinking alone does not show that kidney health has improved.
A stent or bypass system does not remove every need for monitoring. Follow-up checks assess kidney function, urine and, when needed, urine flow through imaging. Report new nausea, pain, weight loss or poor appetite even if toilet visits continue. Any skin or wound changes around the procedure site need separate assessment.
The condition of both kidneys, infections and recovery after treatment affect the outlook. Renal pelvis size alone does not predict how much function will return. Some cats retain chronic kidney disease, with treatment adapted to subsequent results. However, previous kidney disease does not automatically mean that relieving an obstruction cannot help.
Prevention
- Prevent and treat urinary stone disease.
- Pay attention to diet and water availability.
- Arrange regular urine tests and ultrasound examinations to identify changes early.
- Seek veterinary care promptly if your cat shows signs of bladder inflammation or kidney problems.
The need for follow-up tests and their intervals is individual. There is no shared urine-testing and ultrasound programme for every healthy cat to prevent this finding. If stones have been identified, prevention is planned according to their composition and other risk factors. Wet food and good water intake can support the plan, but do not prevent every narrowing or tumour.
Important for cat owners
Ureterectasia and hydroureteronephrosis are dangerous conditions that develop unnoticed and damage the kidneys. Remember that preventing urinary stone disease, timely investigations and monitoring symptoms such as blood in the urine, pain and lethargy help preserve your cat's health.
This article provides general information and does not replace veterinary care. Contact your vet if you notice signs of illness in your cat.
Frequently asked questions
Can a ureter be blocked even if my cat urinates?
Yes. The other kidney may still supply urine to the bladder. The ureter and the urethra leading out of the bladder are different structures, so a normal toilet visit does not rule out an upper urinary tract blockage.
Does an enlarged renal pelvis always mean obstruction?
No. Dilation can occur in other situations, while an obstruction may cause only slight enlargement. Your vet assesses the complete imaging findings, symptoms and laboratory results.
Can a ureteral stone be treated with food alone?
Calcium oxalate stones in cats do not dissolve with diet. An obstruction needs urgent treatment assessment. Diet is used as appropriate to help prevent new stones, rather than as a guarantee that the obstruction will clear.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
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- Feline abdominal ultrasonography: What’s normal? What’s abnormal? Renal pelvis, ureters and urinary bladder, Journal of Feline Medicine and Surgery, accessed 2026-11-05.
- Ultrasonography in the diagnosis and management of cats with ureteral obstruction, Journal of Feline Medicine and Surgery, accessed 2026-11-05.
- Benign ureteral obstruction in cats treated surgically: a retrospective review of 105 cats, Journal of Feline Medicine and Surgery, accessed 2026-11-05.
- Pyelonephritis in Small Animals, Merck Veterinary Manual, accessed 2026-11-05.
- Hydration, Cornell Feline Health Centre, accessed 2026-11-05.
- 2022 ISFM Consensus Guidelines on Management of the Inappetent Hospitalised Cat, Journal of Feline Medicine and Surgery, accessed 2026-11-05.