23 Feb 2015
Ureteral obstruction in cats
Rachel Hattersley
Job Title
In experimental dog models of ureteral obstruction, renal blood flow diminishes by 60 per cent over the first 24 hours and 80 per cent within two weeks, leading to a decrease in the glomerular filtration rate. The contralateral kidney will increase glomerular filtration rate in response, as long as that kidney is normal and has the potential for hypertrophic compensation. After seven days the glomerular filtration rate is permanently diminished by 35 per cent and, after two weeks, by 54 per cent.
However, the majority of cats with nephroureterolithiasis are prolific stone formers and, therefore, previous episodes of ureteral obstruction are not uncommon (Kyles et al, 2005a; Berent et al, 2014). If only one kidney/ureter is affected, clinical signs can often be mild and, therefore, cats will often not present until the second ureter obstructs. This is known as “big kidney little kidney” syndrome, as the previously obstructed kidney is reduced in size. Furthermore, concurrent chronic renal disease is common in cats, thus making the clinical consequences of ureteral obstruction more severe.
Diagnosis
Bloods
Preoperative azotaemia is present in 95 per cent of cats on presentation (Berent et al, 2014). It is important to remember the magnitude of preoperative azotaemia is not correlated with longer term survival (Horowitz et al, 2013; Kulendra et al, 2014). Electrolytes should be monitored as hyperkalaemia is a common finding. PH monitoring, if possible, is also useful – anecdotally, the author’s clinical experience is patients with a marked metabolic acidosis appear to have a worse prognosis. Anaemia is also present in approximately 40 per cent of cases.
Imaging
Plain radiography is useful to document stone size, number, location and the presence of concurrent nephrolithiasis, although the overall sensitivity is only moderate and gas or faeces within the colon can obscure smaller uroliths (Figure 1). Abdominal ultrasonography in combination with plain abdominal radiography is considered to be the gold standard.
When hydroureter tapering to focal point and renal pelvis dilation are present, it is highly likely either a partial or complete ureteral obstruction is present (Figures 2a and 2b). A renal pelvis diameter more than 13mm on the transverse ultrasonographic image is almost always associated with an obstruction, but a diameter more than 8mm should also raise suspicion.
It is important to remember stricture formation can lead to ureteral obstruction and, therefore, a urolith is not always seen. Intravenous and percutaneous pyelography is also reported as part of the diagnostic work-up in previous studies, but in the author’s opinion these provide little additional information and carry the risk of further deterioration in renal function.
Due to the decrease in glomerular filtration rate associated with ureteral obstruction, these techniques are also poor indicators of how renal function will be once the obstruction has been removed. Concurrent nephrolithiasis is common in cats (60 per cent to 86 per cent; Berent et al, 2014).
Management
Medical
Medical management can be considered for 24 to 48 hours in patients that are not anuric, are normokalaemic and do not have metabolic acidosis. This usually consists of intravenous fluid therapy and low-dose prazosin. The use of mannitol constant rate infusions is also reported.
Medical management is only reported to be successful in up to 17 per cent of cases (Kyles et al, 2005b). Progress should be monitored based both on reduction in the degree of azotaemia and also improvement or resolution of the affected renal pelvis and ureteral dilation via ultrasound monitoring.
Surgical options
Surgical options include traditional approaches such as ureterotomy, placement of a double pigtail ureteral stent or a subcutaneous ureteral bypass. It is important to remember each individual will require a different degree of preoperative stabilisation prior to considering surgical management of ureterolithiasis.
As a general rule, surgical intervention should be performed as soon as it is safe to do so to maximise return of renal function, although a slightly longer period of medical management can be considered in partial ureteral obstructions.
Anuria, severe metabolic acidosis and marked hyperkalaemia are all “red flags” for rapid intervention as soon as it is practical. It is important to remember a reasonable proportion of this population will also have concurrent conditions such as cardiac disease and this should be carefully considered when choosing an anaesthetic protocol.
Ureterotomy
Ureterotomy has been the mainstay of treatment for ureteral obstructions in cats for many years. The inner diameter of the feline ureter is 0.4mm and therefore any surgical intervention can prove problematic. A high rate of postoperative complications is reported (31 per cent; Kyles et al, 2005b). An operating microscope or surgical loupes are required for closure of the ureter and small monofilament suture should be used (United States Pharmacopeia sizes 6-0 to 8-0).
Postoperative complications include uroabdomen (in up to 16 per cent of cases), ureteral stricture formation and recurrence of ureteral obstruction (Roberts et al, 2011). Roberts et al (2011) reported survival to discharge from the hospital in 79 per cent of cases. Multivariate analysis of preoperative variables revealed none that were significantly associated with survival to discharge.
Ureteral stent placement
Ureteral stent placement, laser lithotripsy and ureteroscopy are the mainstays of treatment of ureteral obstruction in human medicine and have almost negated the need for open surgical procedures. Ureteral stent placement has been gaining popularity in the veterinary field for both canine and feline patients over the past five years.
Placement of a ureteral stent aims to decompress the renal pelvis and restore urine flow to the bladder, encourage passive ureteral dilation around the stent – which reduces the risk of repeat obstruction – and, finally, to reduce the risk of migration of nephroliths. An indwelling ureteral double pigtail stent is the most commonly used stent in veterinary medicine (Figure 3).
Cystoscopic ureteral stent placement in female cats has been achieved by very experienced operators, but surgical stent placement (via an exploratory celiotomy) is much more common and can either be performed antegrade via pyelocentesis, retrograde via catheterisation of the ureteral papilla or via ureterotomy.
The antegrade technique requires placement of a guide wire into the renal pelvis via surgical pyelocentesis and down the ureter to the bladder under fluoroscopic guidance. The stent is then placed in a retrograde manner from the urinary bladder. The retrograde technique requires catheterisation of the ureteral papilla – again under fluoroscopic guidance and again placement of the stent over the guide wire (Figures 4 and 5).
If the stent or guide wire cannot be advanced past the obstruction, an ureterotomy directly over the point of obstruction is required and the guide wire advanced from within the lumen of the ureter.
Berent at al (2014) reported their clinical experience of ureteral stenting in 69 cats (79 ureters). Ureteral stent placement was successful in 96 per cent of cats and 8.7 per cent of cats had major procedural complications, with uroabdomen representing the majority of these.
Perioperative mortality rate was 7.5 per cent and none of these were considered to be procedurerelated. Stent exchange was required in 27 per cent of ureters in the longer term due to stent occlusion/encrustation, migration or irritation.
Stent encrustation is not uncommon in humans, but passive ureteral dilation usually occurs and therefore urine continues to pass even if the lumen of the stent becomes obstructed. Furthermore, stents are generally only used for short time periods in people. It has been suggested passive ureteral dilation does not occur in ureteral stricture cases, thus obstruction caused by stricture rather than a ureterolith may increase the prevalence of cats requiring stent exchange.
The most common minor complication was temporary stranguria reported in 37.7 per cent of cases, but this was persistent in only one case long term. This is suggested to be secondary to the presence of one end of the pigtail stent within the proximal urethra where the ureterovesicular junction of the cat is situated rather than the bladder trigone as in the dog.
Another publication (Kulendra et al, 2014) reported signs consistent with sterile cystitis in 35 per cent of cases in the longer term. This was considered severe in three of the 26 cats.
Subcutaneous ureteral bypass system
The Subcutaneous Ureteral Bypass (SUB) device (Norfolk Vet Products) has been designed to ameliorate some of the issues seen with ureteral stent placement in cats – particularly the need for stent exchange in the longer term and issues with lower urinary tract signs. This system involves placement of a locking loop pigtail nephrostomy tube (Figure 6) and a cystostomy tube, which are connected via a Huber port (Figure 7), which sits in a subcutaneous location to allow ongoing flushing of the system. A ventral midline celiotomy is performed and the nephrostomy catheter is placed in a minimally invasive manner under fluoroscopic guidance over a hydrophilic guide wire and the cystotomy tube under direct visualisation. The system is checked for patency at the end of the procedure using fluoroscopy (Figure 8).
The SUB system requires ongoing monitoring and the manufacturer’s recommendation is for flushing of the system either under ultrasonographic or fluoroscopic guidance and sampling for urine bacterial culture on a three-monthly basis. The owners should be made aware of this ongoing expense. The newest incarnation of this system now allows replacement of the nephrostomy and cystostomy portions of the tube without disruption to the renal capsule or bladder, respectively.
Complications of this procedure are lower than that reported with traditional ureterotomy. Fluoroscopy is mandatory for placement and there is a relatively steep learning curve initially. In a retrospective analysis of 14 cats, procedure-related complications were relatively infrequent and included leakage (3.5 per cent), kinking (three per cent) and reobstruction with a blood clot (three per cent). Ninety-five per cent of cats survived to discharge (Horowitz, 2013).
Prognosis
As previously stated, no preoperative variables, including the magnitude of creatinine elevation, have been shown to be an accurate predictor of outcome (Roberts et al, 2011; Horowitz et al, 2013; Kulendra et al, 2014).
The vast majority of cats treated for a ureteral obstruction continue to have elevated creatinine levels postsurgery.
Berent et al (2014) reported creatinine level at three months postsurgery was predictive for longer term survival; International Renal Interest Society (IRIS) stage one cats had a survival time of 1,262 days versus 94 days in cats that were IRIS stage four. Kulendra et al (2014) reported a median survival time of 419 days in cats undergoing stent placement for management of ureteral obstruction.
Summary
Recognition of ureteral obstructions in cats is increasing due to an overall increase in the incidence of the disease and as we become more adept at recognising clinical signs. Medical management is rarely successful and the majority of affected cats have multiple nephroliths or ureteroliths.
Surgical management remains the treatment of choice. Interventional techniques carry lower perioperative and postoperative risks than traditional ureterotomy techniques and aim to address issues associated with recurrence.
However, a proportion of cats will continue to have elevated creatinine levels postsurgery (Horowitz et al, 2013; Kulendra et al, 2014).
• Please note some drugs mentioned in this article are not licensed for use in cats and are used under the cascade.
References
- Berent A C, Weisse C W, Todd K and Bagley D H (2014). Technical and clinical outcomes of ureteral stenting in cats with benign ureteral obstruction: 69 cases (2006 to 2010), Journal of the American Veterinary Medical Association 244(5): 559-576.
- Horowitz C, Berent A, Weisse C, Langston C and Bagley D (2013). Predictors of outcome for cats with ureteral obstructions after interventional management using ureteral stents or a subcutaneous ureteral bypass device, Journal of Feline Medicine and Surgery 15(12): 1,052-1,062.
- Kulendra E, Kulendra N and Halfacree Z (2014). Management of bilateral ureteral trauma using ureteral stents and subsequent subcutaneous ureteral bypass devices in a cat, Journal of Feline Medicine and Surgery 16(6): 536-540.
- Kyles A E, Hardie E M, Wooden B G, Adin C A, Stone E A, Gregory C R, Matthews K G, Cowgill L D, Vaden S, Nyland T G and Ling G V (2005a). Clinical, clinicopathologic, radiographic, and ultrasonographic abnormalities in cats with ureteral calculi: 163 cases (1984 to 2002), Journal of the American Veterinary Medical Association 226(6): 932-936.
- Kyles A E, Hardie E M, Wooden B G, Adin C A, Stone E A, Gregory C R, Matthews K G, Cowgill L D, Vaden S, Nyland T G and Ling G V (2005b). Management and outcome of cats with ureteral calculi: 153 cases (1984 to 2002), Journal of the American Veterinary Medical Association 226(6): 937-944.
- Roberts S F, Aronson L R and Brown D C (2011). Postoperative mortality in cats after ureterolithotomy, Veterinary Surgery 40(4): 438–443.
Figure 3. A ureteral double pigtail stent.
IMAGE: Ronan Doyle and Ian Battersby.
Figure 4. Retrograde placement of a ureteral stent over a guide wire.
IMAGE: Ronan Doyle and Rob Adams.
Figure 5. A double pigtail ureteral stent in situ. The yellow arrows denote stent in situ in renal pelvis and trigone; the black arrows denote ureteroliths in situ.
IMAGE: Ronan Doyle and Ian Battersby.
Figure 6. The nephrostomy component of subcutaneous ureteral bypass. The yellow arrow denotes locking loop pigtail, which sits in the renal pelvis; the black arrow denotes the ethylene terephthalate collar, which sits flush with the renal capsule.
Figure 7. The Huber port, which sits in a subcutaneous location and allows ongoing lavage of the subcutaneous ureteral bypass system.
Figure 8. The subcutaneous ureteral bypass system in place. The red arrow denotes nephrostomy tube in situ in the renal pelvis; the yellow arrow denotes the Huber port; the black arrow denotes the cystostomy tube portion of the subcutaneous ureteral bypass.