The Diagnosis and Management of Feline Ureteral Obstruction
Ureteral diseases are being increasingly recognised in our feline patients, mainly due to improvements in diagnostic imaging techniques. In addition to this, developments in interventional techniques have resulted in a number of new management options.
A number of ureteral pathologies are reported in cats:
- Ureteroliths
- Ureteral tumours
- Ureteritis
- Ureteral strictures
- Ectopic ureters & ureterocoeles
The sequel to the majority of these conditions is ureteral obstruction (either partial or complete), which leads to reduced glomerular filtration in the associated kidney. Ureterolithiasis is the cause in at least 90% of cats presented for obstruction, the vast majority of which will be calcium oxalate.
Clinical Presentation of Ureteral Obstruction
- Acute unilateral ureteral obstruction
- Often clinically silent and usually not associated with azotaemia. May be detected in cats presenting with abdominal pain, behaviour changes or haematuria.
- Acute bilateral obstructions
- Relatively uncommon but presents with severe acute signs including enlarged and painful kidneys and severe, progressive azotaemia.
- “Big Kidney-Little Kidney Syndrome”
- Common presentation seen in cats with a previous ureteral obstruction in one kidney (which has progressed to an end-stage fibrotic kidney) and an acute obstruction in the second kidney. Again this presents as abdominal pain and progressive azotaemia.
- Bilateral chronic kidney disease with acute ureteral obstruction
- Acute obstruction causing decompensation of an already reduced renal function. Presents as an acute worsening of azotaemia.
Clinical signs can therefore vary from no signs up to signs consistent with severe uraemia (anorexia, depression, vomiting, lethargy, weight loss, oligoanuria).
Renal Response to Obstruction
Obstruction of the ureter leads to a rapid increase in ureteral pressure, which is transferred to the renal pelvis, this leads to a reduction in renal blood flow. The outcome of this is a rapid reduction in glomerular filtration rate, by about 50% within 4 hours and by 96% at 24 hours. A compensatory increase in glomerular filtration is seen in the contralateral kidney, assuming it is not also obstructed.
The severity of renal damage has been shown to be related to the duration of obstruction. In dogs, a near complete return of renal function occurs after 4 days of obstruction, after 14 days of obstruction the recovery is at around 50% compared to baseline and by 4 weeks significant damage has occurred. As the duration of obstruction is often unknown in our patients it can be difficult to predict where they will fall along this scale.
Diagnosis of Ureteral Obstruction
Signalment:
- Median age of 7 years (range of 8 months to 16 years).
- Clinical Signs:
- Vomiting (93%)
- Lethargy (68%)
- Weight loss (60%)
- PUPD (40%)
- Stranguria/pollakiuria (21%)
- Haematuria (19%)
- Abdominal pain (18%)
- No clinical signs (11%)
- Anaemia (50% of cases)
- Azotaemia (83% of cases)
- Hyperkalaemia (33% of cases)
- Hypercalcaemia (20% of cases)
- Urinary crystals (30% of cases)
- Stone analysis
- 87% calcium oxalate
- 13% mixed (all included calcium oxalate)
- Radiography
- Survey radiographs
- Intravenous urography
- Antegrade pyelography
- CT scan
- Abdominal ultrasound
- Assess the renal pelvis for dilation. The normal feline renal pelvis is between 0.8 and 3.2mm. A renal pelvis of greater than 13mm was always associated with obstruction in one study.
- Also allows assessment of the ureter for dilation, which may allow identification of the site of obstruction.
- Diagnostic in approximately 90% of cases.
None of these modalities reliably predicts the long-term outcome after ureteral obstruction, meaning that there is an element of uncertainty to any treatment decisions.
Management of Ureteral Obstruction
Medical management should be initiated immediately after diagnosis of a ureteral obstruction, in order to stabilise the patient and attempt to relieve the obstruction. It should, however, be noted that it is only reported to be successful in 17% of cats with obstruction.
Medical management:
If no response is seen to medical management over 24 hours then it is unlikely to be successful. In that event a more definitive treatment should be undertaken as soon as possible, options for this include:
Interventional procedures:
Traditional surgical procedures carry a peri-surgical mortality of around 30% and also do not allow the prevention of reobstruction, which is reported in 40% of cats.
Interventional procedures are therefore currently considered the treatment of choice for ureteral obstruction in cats and are successful in around 95% of cases. Whilst both ureteral stenting and SUB placement are successful in the majority of cases, the current evidence suggests that stent placement may have a higher incidence of long-term complications (primarily lower urinary tract signs) and so SUB placement is preferred.
I have now placed SUBs in a number of cats and agree that the incidence of longer-term complication seems to be lower. However it does require a big commitment from the owner as frequent visits to us are required to monitor the device for the rest of the cat's life.
If you are interested in seeing how SUBs are placed then have a look at the video from Norfolk Vet Products (makers of the SUB) at the bottom of the page.
Postoperative Management:
Long-term Management:
This is dependent on the cause of obstruction and the renal function after treatment. The majority of cats will require management of chronic kidney disease longer term and, potentially, management to reduce the likelihood of stones reforming.
Cats with stents or SUBs also require regular follow-up to ensure the device continues to work as expected. The median reported survival time in cats after interventional management is 498 days (2->1278) but is dependent on remaining renal function.
Medical management should be initiated immediately after diagnosis of a ureteral obstruction, in order to stabilise the patient and attempt to relieve the obstruction. It should, however, be noted that it is only reported to be successful in 17% of cats with obstruction.
Medical management:
- Aggressive intravenous fluid therapy, ideally with monitoring of electrolytes, central venous pressure, body weight and hydration status.
- Consider administration of an osmotic diuretic, most commonly mannitol.
- Spasmolytics:
- α-1 adrenergic antagonists
- Tamsulosin
- Prazosin
- Smooth muscle relaxants
- Amitriptyline
- α-1 adrenergic antagonists
- Analgesia
If no response is seen to medical management over 24 hours then it is unlikely to be successful. In that event a more definitive treatment should be undertaken as soon as possible, options for this include:
Interventional procedures:
- Subcutaneous ureteral bypass (SUB) device
- Ureteral stent
- Temporary nephrostomy tube placement
- Ureterotomy
- Ureteral reimplantation
- Ureteronephrectomy
Traditional surgical procedures carry a peri-surgical mortality of around 30% and also do not allow the prevention of reobstruction, which is reported in 40% of cats.
Interventional procedures are therefore currently considered the treatment of choice for ureteral obstruction in cats and are successful in around 95% of cases. Whilst both ureteral stenting and SUB placement are successful in the majority of cases, the current evidence suggests that stent placement may have a higher incidence of long-term complications (primarily lower urinary tract signs) and so SUB placement is preferred.
I have now placed SUBs in a number of cats and agree that the incidence of longer-term complication seems to be lower. However it does require a big commitment from the owner as frequent visits to us are required to monitor the device for the rest of the cat's life.
If you are interested in seeing how SUBs are placed then have a look at the video from Norfolk Vet Products (makers of the SUB) at the bottom of the page.
Postoperative Management:
- Monitor closely for postobstructive diuresis
- Consider the placement of feeding tubes to ensure adequate nutrition.
- Monitor electrolytes and creatinine
Long-term Management:
This is dependent on the cause of obstruction and the renal function after treatment. The majority of cats will require management of chronic kidney disease longer term and, potentially, management to reduce the likelihood of stones reforming.
Cats with stents or SUBs also require regular follow-up to ensure the device continues to work as expected. The median reported survival time in cats after interventional management is 498 days (2->1278) but is dependent on remaining renal function.