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Treating feline ureteral obstruction

The second of this two-part series explains how to treat ureteral obstruction – an under-recognised condition in cats

22 July 2018, at 9:08pm

Most cases of feline ureteral obstructive disease (UO) will require referral to a specialist centre with the skills and expertise to deal with this challenging condition. This includes preoperative, intraoperative and post-operative care, all of which require an intensive care facility. The cat may remain hospitalised for approximately 5 to 10 days depending on the complexity of surgery, any pre-existing renal disease and complications encountered.

If referral is not considered an option due to financial reasons or the owner’s wishes, medical management may be considered for three to five days, providing the cat is not oliguric, anuric, hyperkalaemic or overhydrated. Clinical evidence suggests that resolution of ureteral obstruction occurs in approximately 8 to 13 percent of cats that are medically managed. 

Medical management

Ureteral obstruction is incredibly painful, so effective analgesia (typically opioids) must be provided at all times until the obstruction has been relieved and the patient is more comfortable. 

Medical management of UO involves judicious fluid therapy with or without diuretics (furosemide or mannitol with the aim that the diuretic increases glomerular filtration rate and raises the intraureteral luminal pressure, thus pushing the ureteroliths/dried solidified blood into the urinary bladder where it can be either more easily removed or voided). These patients are at a higher risk of volume overload and increased pressure on the renal pelvis if a total UO is present. In addition to fluid therapy to try to restore renal perfusion and correct dehydration, supportive care for uraemic consequences should be considered (antacids, antiemetics, etc). 

Many specialists in this area consider that as soon as the cat is stabilised, surgery should be performed to minimise further nephron damage caused by the combination of the complete obstruction and excessive fluid therapy. As a general rule, cats that have shown no response to diuresis after 24 to 48 hours should undergo surgical intervention where possible. When referral for surgery is not an option and the cat is not hyperkalaemic, anuric or volume overloaded (generally cats with unilateral obstruction or partial obstructions), then medical management can be trialled for three to five days. 

Prazosin (α1-antagonist) is also a potent smooth muscle relaxant and α1-antagonists are considered the standard of care for inducing human ureteral dilation. Again, limited studies are available to assess the efficacy of this class of drug in treating feline ureteral spasm but it may be of benefit in those patients that can only be treated using medical management. The dose range varies from 0.25 to 0.5mg/cat q12 to 24 hours. Blood pressure must be assessed prior to starting the drug and closely monitored for the first few days after initiation of treatment to ensure there is no development of hypotension. Consideration should also be given to treatment of any UTI that is detected on urine culture.

If medical management fails to encourage stone passage (monitored by ultrasound and radiography), immediate resolution of the obstruction at a referral centre should be considered as detailed below. It is also important to note that 20 percent of feline UOs are caused by ureteral strictures (most of which are in the proximal ureter), for which medical management will not be effective. Consideration should also be given to the fact that a proportion of ureteric stones will be embedded in the ureteric mucosa, hence passage of the stone will be unlikely. 

Surgical management 

The three surgical options described below are complex procedures and require considerable experience and specialist equipment as well as a highly skilled team providing intensive care. They are described here for information only so that an informed discussion can be had with the owner regarding possible options and complications prior to considering referral (this will also be discussed at length by the specialist team at the referral appointment). 

Traditional techniques 

Surgery to directly remove the ureterolith(s) has traditionally been performed by coeliotomy; however, due to high rates of mortality (20 percent) and complication (33 percent) compared to the other more sophisticated procedures detailed below, this form of surgery is now rarely performed. A full examination of the urinary tract should be completed as multiple ureteroliths may be present (note also the bladder and kidneys should have been assessed with imaging for uroliths). A recent large study revealed that cats had a median of four ureteroliths and 86 percent of cats also had ipsilateral renoliths. If the ureterolith(s) is in the proximal ureter, it may be flushed back to the renal pelvis by performing a cystotomy and catheterising the ureter. The ureterolith is then removed via a pyelotomy, which is technically easier and less likely to result in ureteral inflammation/spasm/stenosis/stricture. 

Distal ureteric obstructions can be managed by ureterectomy of the affected portion of ureter and re-implantation of the remaining ureter into the apex of the bladder (neoureterocystotomy). Ureteronephrectomy is not a viable treatment option in these cases as more than 75 percent of cats are azotaemic at the time of presentation, implying dysfunction of the contralateral kidney, hence renal function needs to be preserved as much as possible. 

Mortality rates are approximately 20 percent for cats undergoing traditional surgical management of ureteroliths. It should be noted that survival rates for surgery are better than those receiving medical management alone (33 percent mortality rate), with 91 percent of cats who survived the first month following diagnosis alive after 12 months compared to 66 percent of cats who received medical management alone. Complications are seen in around a third of cats and include oedema/inflammation at the ureterovesical junction, ureteral stricture, uroabdomen and persistent obstruction. Urine leakage is the most common problem and occurs in approximately 16 percent of cases.

Complications are seen in approximately a third of cats and include oedema/inflammation at the ureterovesical junction, ureteral stricture, uroabdomen and persistent obstruction

Forty percent of cats have a further ureteral obstruction, most likely due to previously undetected nephroliths. 

Stents

Stents are becoming less commonly performed in the UK. They are polyurethane tubes containing multiple fenestrations that are inserted into the ureter. The stent has a pigtail at either end with one end secured in the renal pelvis and the other secured at the ureteric opening into the bladder trigone (Figure 1). The stent provides passive ureteric dilatation and urine can flow either through or around it. Stents can be very challenging to place and surgical times can be prolonged. There may also be a high rate of dysuria because of the position of the pigtail in the bladder trigone area. Perioperative mortality rates after stent surgery are significantly lower (7.5 percent) than traditional surgical techniques (20 percent).

FIGURE 1 One end of the ureteral stent is secured in the renal pelvis and the other is secured at the ureteric opening into the bladder trigone
FIGURE 1 One end of the ureteral stent is secured in the renal pelvis and the other is secured at the ureteric opening into the bladder trigone

Subcutaneous ureteral bypass system 

This is a tube that completely bypasses the obstructed ureter, effectively creating a false ureter. It is more commonly performed in the UK and is now considered the treatment of choice by highly experienced specialists at the Animal Medical Centre, New York. The subcutaneous ureteral bypass (SUB) was developed as an alternative to ureteral stents when either a stricture was present (which resulted in more than 50 percent stent occlusion) or when a stent could not be successfully placed due to excessive stones, a narrow ureteric lumen or patient stability. 

A pigtail catheter is inserted into the renal pelvis and connected to a subcutaneous access port. A separate pigtail catheter is also inserted into the bladder and this tube is also connected to the subcutaneous access port (Figure 2). This procedure has been highly successful for the treatment of all causes of feline UO (strictures, stones, tumours, obstructive pyelonephritis). This surgical procedure is technically simpler with a shorter surgery time (45 to 60 minutes with experienced specialists). In terms of long-term patient comfort and complications, SUBs were found to be superior to stents in a recent study (less dysuria and stent occlusion).

FIGURE 2 For SUB placement, a pigtail catheter is inserted into the renal pelvis and connected to a subcutaneous access port. A second catheter is also inserted into the bladder, which is also connected to the subcutaneous access port
FIGURE 2 For SUB placement, a pigtail catheter is inserted into the renal pelvis and connected to a subcutaneous access port. A second catheter is also inserted into the bladder, which is also connected to the subcutaneous access port

Perioperative mortality rate after surgery was 6.2 percent in a recent study, which compares well to traditional surgery (20 percent) and stenting (7.5 percent). Postoperative complications were rare and included urine leakage (4 percent), kinking of the catheter (5 percent) and blockage of the system with either blood clots (8 percent), debris, purulent material or mineralisation (24 percent). Dysuria is rarely seen with SUBs (6 percent) compared to ureteral stents (38 percent). 

Appropriate post-operative management is essential for a good outcome. Post-obstructive diuresis is common in these patients, hence this needs to be appropriately managed with fluid therapy. Intensive monitoring is essential to avoid fluid overload, which can lead to congestive heart failure. This is one of the main post-operative complications associated with management of ureterolithiasis in cats (despite normal echocardiogram in most cats). Abdominal palpation should also be avoided for two weeks postoperatively and cystocentesis should not be performed in these patients. Urine culture should be performed on a urine sample obtained from the SUB port at the time of routine flushing (which is typically performed every three to six months at the referral centre). 

Nephrostomy tube 

A nephrostomy tube can be placed to immediately relieve the intra-ureteric/pelvic pressure with the aim of rapidly resolving azotaemia. This may be performed as an emergency procedure on arrival at the referral centre to minimise further nephron damage while stabilising the cat prior to surgery. A locking loop pigtail catheter is surgically placed with fluoroscopic guidance. The locking loop pigtail mechanism has resulted in a significant reduction in complications associated with this tube placement (previously due to premature removal/displacement of the tube, urine leakage and poor drainage). 

Some specialists with considerable UO experience will now progress straight to SUB placement as the time taken for this procedure is similar to nephrostomy tube placement (approximately 45 to 60 minutes with experience) and also negates the need for two anaesthetics in a renally compromised patient. 

Lithotripsy 

This treatment has been used successfully in dogs but the feline kidney is more sensitive to shock wave-induced injury. Also note that the intraluminal diameter of the feline ureter is incredibly small, measuring only 0.4mm, and along with technical challenges due to the size of the ureter, structural damage can occur due to an inflammatory response being incited at the site of lithotripsy and subsequent ureteral stricture formation. 

Prognosis 

The main factor that affects the outcome of these cases is the severity of the kidney disease as a result of the obstruction. The earlier UO is detected (ideally prior to complete obstruction and secondary renal damage) the more likely a good outcome will be achieved. Cats with IRIS stage 1 or 2 CKD have a good long-term outcome. 

The author hopes that this article series will highlight the likely higher incidence of this under-recognised condition. Any cat that has apparent rapidly advancing CKD (ie an increase in IRIS renal stage over a short time period) or “big kidney-little kidney syndrome” should be urgently investigated for UO. If both veterinary and owner awareness of this condition can be increased, earlier detection and intervention can be sought, resulting in a much more favourable outcome.

Director at European School of Veterinary Postgraduate Studies

Sheila Wills, BVetMed, CertSAM, DipECVIM-CA, MRCVS, is an EBVS European Veterinary Specialist in Small Animal Internal Medicine and an RCVS Specialist in Feline Medicine. She joined the European School of Veterinary Postgraduate Studies in 2017.

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