Contributors: Melissa Wallace, Aidan B McAlinden, Julien Bazelle

 Species: Feline   |   Classification: Diseases

Introduction Pathogenesis Diagnosis Treatment Outcomes Further Reading


  • Causes:
    • Intraluminal: urolithiasis (most common), solidified blood clots/pus, ureteritis.
    • Intramural: tumors (rare), strictures (fibrosis).
    • Extramural: abdominal tumors, ligation, uterine stump infections, trauma, ectopic ureterocele.
  • Signs: dysuria, hematuria, depression, vomiting, dehydration if renal failure present. Obstruction of a single ureter can also be clinically silent.
  • Treatment: identify and correct acid base/electrolyte abnormalities, establish diuresis. Remove obstruction (often surgical) or divert urinary flow (SUB device).
  • Stenting has been described which is minimally invasive, potentially avoids some surgical risks and can be successful.
  • Subcutaneous Ureteral Bypass surgery allows to divert the urine from the renal pelvis into the bladder, bypassing the blocked ureter and restoring kidney function. 
  • Prognosis: prolonged obstruction (>7 days)   →   permanent kidney damage. Renal damage increases with duration of obstruction.

Presenting Signs

Acute Presentation

  • Anuria (if bilateral).
  • Flank pain, abdominal pain.
  • Depression, weakness, vomiting.

Cost Considerations

  • Bilateral ureteral obstruction   →   emergency surgery, treatment of obstructive uropathy.



  • Intraluminal: urolithiasis Urolithiasis, solidified blood clots, inflammation and inflammatory debris (bacterial ureteritis, pyelonephritis Pyelonephritis).
  • Intramural: tumors of the ureter (not reported), strictures (secondary to ureteritis or ureterolithiasis), neoplasia or polyps at ureteral opening in the trigone.
  • Extramural:


  • Prolonged partial ureteral obstruction   →   dilation of proximal segment and hydronephrosis Hydronephrosis / hydroureter and fibrosis   →    reduction in renal blood flow and GFR Glomerular filtration rate   →    ultimately tubular dilation and interstitial fibrosis.
  • If complete ureteral obstruction is relieved within 7 days in experimental studiesin experimental studies   →   little permanent damage. Correction of complete obstruction at 4 weeks   →   renal function recovers to 30% of normal GFR.
  • Bilateral obstruction   →   azotemia Azotemia, uremia Uremia  →   eventual acute intrinsic renal failure Kidney: acute renal failure.


  • Correction within 7 days in experimental studies  →   little permanent damage.


Diagnostic Investigation


  • See abdominal radiography Radiography: abdomen.
  • Plain radiographs: some uroliths, eg calcium oxalate (most common in cats).

2-D Ultrasonography

Contrast Radiography


Standard Treatment


  • See also urolithiasis Urolithiasis.
    • Can attempt initial medical management and monitor for the urolith(s) to pass.
    • Treat with intravenous fluid therapy.
    • Consider pharmacological ureteral relaxation (eg phenoxybenzamine Phenoxybenzamine), pain management (eg opioids Analgesia: opioid), nausea control (eg maropitant Maropitant citrate).
    • Need to balance duration of medical therapy against progressive renal damage.
  • Relieve obstruction:
    • To remove ureterolith if it fails to pass with medical management, ureterotomy was historically considered but is no longer recommended in most cases due to surgical procedures associated with less complications. Incision should be made over the urolith. May need to make a longitudinal incision and close transversely to reduce the risk of stenosis. Placement of a temporary nephrostomy tube may be required in the post-operative period. A piece of 4/0 suture material can be placed into the lumen as a temporary stent to prevent suturing the far wall. This is removed before the final suture is placed. Require 7/0-10/0 absorbable suture for cats.Fine ophthalmological instruments and magnification required. Complications include stenosis, ureteritis, hematuria, pain and wound complications.
    • Ureteral double pigtail stents Ureter: obstruction - surgical management may be placed in a minimally invasive manner using fluoroscopic guidance to restore ureteral urine flow. May be placed normograde via the kidney or retrograde through a small cystotomy Cystotomy. Typically only available at specialist centers. The urolith does not require removal and this avoids the risk of stricture associated with ureterotomy. Complications include ureteritis, infection of the stent, hematuria, migration of the stent, blockage.
    • Subcutaneous Ureteral Bypass devices are used to restore the urinary flow by bypassing the blocked ureter. It consists in two tubes connected by a subcutaneous port. The cranial tube is inserted within the renal pelvis while the caudal tube is inserted in the bladder. The subcutaneous port allows urine sampling and flushing of the device to confirm patency. Complications include infection of the device, hematuria, obstruction, fracture of the tubing, uroabdomen.  
    • Temporary nephrostomy catheters to relieve obstructive uropathy considered in some cases.
  • Lithotripsy:
    • Not beneficial in cats.
    • Need to reduce so much to reduce potential for renal injury that there is a loss of efficacy.
    • Not widely available.


  • Neoplasia of ureter (rare) Ureter: neoplasia.
  • Ureteronephrectomy Ureteronephrectomy required for confirmation of the diagnosis and treatment.
  • May be possible to consider partial ureterectomy and neoureterocystostomy if the lesion is close to the bladder.
  • A similar approach may be taken for distal ureteroliths with severe fibrosis.


  • Treatment aimed at the primary condition.
  • Removal of an extra-mural tumor may relieve the space occupying effect and restore flow in acute cases.
  • Chronic ureteral ligation often associated with end-stage hydronephrosis and/or pyelonephritis and likely to require ureteronephrectomy.


  • Azotemia, metabolic acidosis Acid base imbalance, hyperkalemia Hyperkalemia or hypokalemia Hypokalemia due to post-obstruction diuresis and renal insufficiency.
  • Urine production.
  • In case of stent and SUB devices, regular abdominal ultrasound and urinalysis (including from urine collected by the subcutaneous port for the SUB device). Renal pelvis dilation is partially reversible in the absence of obstructive complication. 

Subsequent Management



  • Serial intravenous pyelograms (excretory urograms).
  • Repeat blood sampling for urea Blood biochemistry: urea, creatinine Blood biochemistry: creatinine, and electrolyte measurement.
  • Repeat urinalysis for assessment of specific gravity Urinalysis: specific gravity and rule out infection.
  • In case of placement of a SUB device, regular flushing of the device using Huber needle is recommended. Infusion of EDTA was reported to decrease mineralization and secondary obstruction of SUBH devices.  
  • SUB devices and stent are associated with high frequency of post-operative complications (such as infection, bleeding, obstruction of the device) however these are often medically manageable.



  • Some uretoliths pass without surgical intervention.
  • If less than 7 days obstruction in experimental studies  →   little permanent damage.
  • More than 7 days obstruction in experimental studies  →   permanent kidney damage likely, eg 30% renal function after 4 weeks obstruction.
  • Prognosis after depends on unilateral vs bilateral and degree of renal insufficiency.
  • Impossible in many cases to know how long the obstruction has been present and therefore it is not possible to predict reversibility of the azotemia pre-operatively.
  • If a patient is azotemic with unilateral obstruction then this suggests bilateral renal insufficiency/failure.
  • Chronic obstruction may lead to ureteral rupture and uroabdomen or retroperitonitis.
  • See also trauma of ureter Ureter: trauma.
  • Depends on tumor type.

Expected Response to Treatment

Reasons for Treatment Failure

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Kulendra N J, Borgeat K, Syme H, Dirrig H, Halfacree Z (2021) Survival and complications in cats treated with subcutaneous ureteral bypass. JSAP 62(1), 4-11 PubMed.
  • Vrijsen E, Devriendt N, Mortier F, Stock E, Van Goethem B, de Rooster H (2020) Complications and survival after subcutaneous ureteral bypass device placement in 24 cats: a retrospective study (2016-2019). J Feline Med Surg ePub PubMed.
  • Chik C, Berent A C, Weisse C W, Ryder M (2019) Therapeutic use of tetrasodium ethylenediaminetetraacetic acid solution for treatment of subcutaneous ureteral bypass device mineralization in cats. J Vet Intern Med 33(5), 2124-2132 PubMed.
  • Fages J, Dunn M, Specchi S, Pey P (2018) Ultrasound evaluation of the renal pelvis in cats with ureteral obstruction treated with a subcutaneous ureteral bypass: a retrospective study of 27 cases (2010-2015). J Feline Med Surg 20(10), 875-883 PubMed.
  • Berent A C (2011) Ureteral obstructions in dogs and cats: a review of traditional and new interventional diagnostic and therapeutic options. J Vet Emer Crit Care 21 (2), 86-103 PubMed.
  • Zaid M S, Berent A C, Weisse C et al (2011) Feline ureteral strictures: 10 cases (2007–2009). J Vet Intern Med 25, 222-229 PubMed.  
  • Kyles A E, Hardie E M, Wooden B G et al (2005) Management and outcome of cats with ureteral calculi: 153 cases (1984-2002). JAVMA 226 (6), 937-944 PubMed.
  • Kyles A E, Hardie E M, Wooden B G et al (2005) Clinical, clinicopathologic, radiographic, and ultrasonographic abnormalities in cats with ureteral calculi: 163 cases (1984-2002). JAVMA 226 (6), 932-936 PubMed.
  • Nwadike B S, Wilson L P & Stone E A (2000) Use of bilateral temporary nephrostomy catheters for emergency treatment of bilateral ureter transection in a cat. JAVMA 217 (12), 1862-1865 PubMed.
  • Kyles A E, Stone E A, Gookin J et al (1998) Diagnosis and surgical management of obstructive ureteral calculi in cats - 11 cases (1993-1996). JAVMA 213 (8), 1150-1156 PubMed.
  • Lamb C R (1998) Ultrasonography of the ureters. Vet Clin North Am Small Anim Pract 28 (4), 823-848 PubMed.

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