Ureteral Obstruction in Cats

Ureteral obstruction has been previously considered an uncommon occurrence in cats. With wider availability of advanced imaging, particularly ultrasonography, the diagnosis of ureteral obstruction appears to be increasing in incidence (Kyles et al, 2005).

Ureteral obstruction occurs secondary to an intraluminal obstruction, a mural lesion, or extraluminal compression.  Mural lesions include neoplasia, fibrosis, congential and acquired stricture and polyps. Extraluminal compression most often occurs secondary to neoplasia arising from the ureter, the bladder, or the retroperitoneal space however there is also a report of an occurrence secondary to retroperitoneal infarction and fibrosis (Ragni and Fews, 2008). Examples of intraluminal obstruction include calculi, debris, and spasm of the ureter. 

Intraluminal obstruction may occur unilaterally or bilaterally. Ureteral obstruction regardless of the underlying cause leads to restriction of urine flow, and if left untreated, obliteration of the renal parenchyma secondary to pressure.  The physiology of ureteral obstruction has been studied in dogs and revealed that the prognosis for recovery of renal function is dependent on both the degree of obstruction and the time that obstruction is in place. After four days of obstruction the prognosis for return of renal function is excellent, after 14 days there will only be a recovery of approximately half of the normal glomerular filtration rate, and after 40 days there is little or no recovery if the obstruction is corrected (Kyles, 2006). 

This highlights the need for prompt diagnosis and intervention. Unilateral obstructions are difficult to diagnose as renal function remains normal due to the efforts of the contralateral kidney. Unfortunately if the first obstruction is unilateral the cat is often left undiagnosed until a second obstruction occurs in the contralateral kidney resulting in renal failure (Evans et al 2007).

Clinical signs of cats presenting with ureteral obstruction may be vague. Presenting complaints include lethargy, vomiting, inappetance, and weight loss. The most common finding on physical examination is abdominal/spinal pain.  In cases where there has been previous undiagnosed obstruction one large kidney may be palpated and the contralateral kidney may be unable to be detected (“big kidney-little kidney” presentation). 

In the author’s opinion, any cat that upon abdominal palpation one large kidney and one small kidney are palpated should have renal imaging performed. Pyrexia and dehydration may also be clinical examination findings in cases where ureteral obstruction is occurring as a consequence of debris generated by pyelonephritis. In cats presenting with ureteral obstruction for the first time, physical examination findings may be very subtle and a high index of clinical suspicion needed for diagnosis.

Biochemical changes of ureteral obstruction can range from unremarkable through to severe azotemia (from acute renal failure). Bilateral obstructions usually have significant azotemia as neither kidney can function. Unilateral obstructions usually have unremarkable biochemical changes if the contralateral kidney is unaffected where as they will have severe azotemia if the contralateral kidney is non-functional. Clinical pathology may demonstrate severe renal dysfunction but cannot differentiate ureteral obstruction from other forms of acute renal failure. Common laboratory findings include severe azotemia, hyperphosphatemia, and hyperkalaemia.

Any cat presenting with these clinical pathology changes should be considered an emergency.  While there are many causes of acute renal failure it is the authors opinion that imaging of the urinary tract should be mandatory for any cat with acute renal failure. Urine specific gravity (USG) is often suboptimal in these cats (< 1.035).  Urine sediment should be examined for concurrent bacterial infection and urine should be sent for culture and sensitivity.

Definitive diagnosis of ureteral obstruction may be made via several different imaging modalities.  Ureteral calculi are often visible on plain abdominal radiographs.  A retrospective study revealed that sonography and survey radiography used in combination was able to diagnose 90% of ureteral calculi (Kyles et al, 2005). 

Sonography will reveal dilation of the renal pelvis greater than 3mm.  Occasionally the cause of obstruction may be visualised sonographically, for example the visualization of a bladder mass or calculus within the proximal ureter.  In the absence of visualisation of the cause of suspected obstruction, an antegrade positive contrast pyelogram should be performed.  Intravenous urography does not usually provide suitable images. A three-way tap is connected to: a 3ml syringe filled with suitable contrast material (eg Urograffin or Omnipaque) an empty 3ml syringe (for fluid collection) and a long 22 guage needle (2 ¼ inch).

Under ultrasound guidance the needle is inserted through the greater curvature of the kidney into the renal pelvis.  Urine is aspirated from the renal pelvis into the empty syringe and retained for sediment analysis and culture and sensitivity.  Once urine is collected, the 3-way tap is turned and contrast is injected into the renal pelvis.  Lateral and dorsoventral abdominal radiographs are then performed. Where ureteral obstruction exists there will be abrupt termination of the contrast column. In some cases, particularly those where obstruction is secondary to pyelonephritic debris the obstruction may be flushed under pressure into the bladder.  Other methods of diagnosis include advanced imaging such as CT, MRI and nuclear scintigraphy.

Treatment of ureteral obstruction varies depending on the underlying cause. The following notes discuss treatment of treatment of intraluminal obstruction secondary to calculi or debris only.

Intraluminal ureteral obstruction may be treated medically or surgically. 

First and foremost pain relief is MANDATORY for cats with ureteral obstruction. It is amazing how many angry aggressive cats seemingly change personality overnight with the administration of pain relief. The most common analgesics used for ureteral obstruction at The Cat Clinic are the opiates methadone (used in intermittent bolus dosing) and fentanyl patches (Durogesic patch, 12.5microgram or 25 microgram depending upon the size of the cat).

The mainstay of medical therapy involves judicious use of intravenous fluids and agents to dilate the ureter to promote passage of the obstruction. There are two distinct groups of cats that are medically treated. The first group are those presenting with their first episode of obstruction, or those cats who have compromise of the contralateral kidney and are azotemic but not hyperkalaemic on presentation. The second group of cats are those who present in acute renal failure with hyperkalaemia. These cats have either bilateral obstruction or unilateral obstruction with little or no function of the contralateral kidney.

At The Cat Clinic non-hyperkalaemic cats are treated with intravenous fluids and ureteral dilating agents initially.  Cats that do have compromise of the contralateral kidney are at risk for oliguric or anuric renal failure.  As such body weight should be closely monitored (the author recommends every 4-6 hours). Obviously another method of monitoring urine output is to place an indwelling urinary catheter and monitor urine output. 

The authors do not routinely place urinary catheters in these cats for the following reasons; these cats are usually relatively bright and sedation/anaesthesia is often required for catheter placement, and the placement of a urinary catheter opens up a potential site of infection. Cats are maintained on intravenous fluids for a maximum of three days.  Agents used to stop ureteral spasm, dilate the ureter or increase urine flow include amlodipine, amyltriptaline, glucagon and diuretics. Further study into the clinical efficacy of these drugs is needed.

Daily monitoring of packed cell volume (PCV), total protein (TP), creatinine and serum electrolytes (sodium, potassium, and chloride) should be performed.  It is vital to track changes in electrolytes in these cats.  The majority of cats are re-imaged via sonography on day three. 

Our criteria for successful medical therapy are 1. Reduction in creatinine to normal or previously determined baseline level and 2. Reduction in size of renal pelvis. 

If the patient has not responded to therapy within three days then surgical intervention should occur.  Cats that progress to hyperkalaemic acute renal failure within this three day period should be considered candidates for surgery post stabilisation.

Cats presenting with hyperkalemic acute renal failure are candidates for surgery following stabilisation.  Intravenous fluid therapy should be commenced with non-potassium containing fluids. Close attention should be paid to the body weight and hydration status of the cat as it is very easy to fluid overload these cats. Depending on the level of hyperkalaemia and the state of the patient, additional therapy for hyperkalaemia may need to be instituted. Therapies include the administration of regular insulin and glucose intravenously and sodium bicarbonate. Calcium gluconate may utilised for its cardioprotective qualities where appropriate.

After the initial period of stabilisation the decision must be made whether the patient is stable enough for a long surgical period, or if peritoneal dialysis or percutaneous nephrostomy tube placement should be attempted. This decision is based upon individual patient factors.

There are several different surgical techniques for relief of ureterliths. The choice of technique is dependent upon the location of the obstruction.  In humans there are three specific sites where ureteroliths tend to lodge. As yet it is not yet determined if such sites exist in cats (Kyles, 2006). Obstructions in the proximal ureter are usually removed via uretotomy.  Given the size of the feline ureter magnification is essential during surgery. 

At The Cat Clinic, an operating microscope is routinely used for this surgery.  Ureteroliths in the distal ureter may be treated via uretotomy or ureteroneocystostomy (transection and then reimplantation of the ureter into the bladder).  The most common post operative complications seen at The Cat Clinic is uroabdomen (Evans et al, 2007). This is also the most common surgical complication seen at the University of California, Davis (Kyles et al, 2005). Other reported complications include pulmonary oedema, septic peritonitis, and persistant ureteral obstruction. Nephrostomy tubes divert urine away from ureterotomy site and allow for rapid reduction in azotemia. At The Cat Clinic, experience with uroabdomen has led us to routinely place nephrostomy tubes however surgeons at UC Davis feel this is not necessary with improved surgical technique. Nephrostomy tubes are associated with complications including obstruction of the tube, dislodgment of the tube, urine leakage, and infection.

Other therapies for resolution of ureteral obstruction include the use of extracorporeal shock wave lithotripsy. The University of California, Davis had been using this treatment method with informed consent of the owner of the patient.  However it is associated with high rates of complications including sudden death, pancreatitis, diarrhea, and cardiac arrythmias. The researchers also found that feline ureteroliths were generally “harder to fracture” than canine ureteroliths and thus this treatment methodology is not favoured (Hardie and Kyles, 2004). There has also been a case report of endoscopic retrieval of a ureteral calculus (Kuntz, 2005).

Kyles et al 2005 reported twelve month survival rates of 66% for those cats treated medically, and 91% for those cats treated surgically. This study also reported that of 35 cats monitored post obstruction 14 had a recurrence of ureterolithiasis. This occurred a median of 12 months post first obstructive episode. 

At The Cat Clinic approximately 1 in 3 cats treated for an episode of ureteral obstruction will have a recurrence of clinical signs.  Data is not yet available with regard to long term survival.

Ureteral obstructions can be treated medically and surgically with good outcomes, however recurrence is very common (Kyles et al, 2005, Evans et al, 2007).  With non specific clinical signs a high index of suspicion may be needed for diagnosis. Prompt diagnosis and intervention minimises long term damage to the affected kidney. Diagnosis is aided by imaging techniques such as radiography and sonography.  It is important that any cat with signs of an acute abdomen be imaged.


Evans, N.A. Gunew, M. Marshall, R. Ureteral obstructions can be treated medically and surgically with good outcomes.  Proceedings of the Australian College of Veterinary Scienctists 2007.

Hardie, E.M. and Kyles, A.E.  2004.  Management of ureteral obstruction
Vet Clin North Am Small Anim Pract. 34(4):989-1010.

Kuntz, C.A.  2005.  Retrieval of ureteral calculus using a new method of endoscopic assistance in a cat.  Aust Vet J.  83(8):480-2.

Kyles, A.E., Hardie, E.M., Wooden B.G., Adin C.A., Stone E.A., Gregory C.R., Mathews K.G., Cowgill L.D., Vaden S., Nyland T.G., Ling, G.V.  2005.  Clinical, clinicopathologic, radiographic, and ultrasonographic abnormalities in cats with ureteral calculi: 163 cases (1984-2002).  J Am Vet Med Assoc. 226(6):932-6.

Kyles, A.E., Hardie, K.M., Wooden, B.G., ., Adin C.A., Stone E.A., Gregory C.R., Mathews K.G., Cowgill L.D., Vaden S., Nyland T.G., Ling, G.V.  2005.  Management and outcome of cats with ureteral calculi: 153 cases (1984-2002).  J Am Vet Med Assoc. 226(6):937-44.

Kyles, A. E.  2006.  Renal and Ureteral Obstruction.  Proceedings if the British Small Animal Veterinary Congress 2006.

Ragni, R.A., Fews, D. 2008.  Ureteral obstruction and hydronephrosis in a cat associated with retroperitoneal infarction.  J Feline Med Surg. In press.

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