14 | companion SEPTEMBER 2014 | BSAVA 2014

How to manage feline ureteric obstruction

AetiologyCalculi are the most common cause of ureteric obstruction in cats. Other causes reported include neoplasia, strictures, trauma and iatrogenic ligation following ovariohysterectomy.

The majority (>98%) of ureteral stones are formed from calcium oxalate. Calcium oxalate stones that do not pass spontaneously need to be removed surgically as they cannot be dissolved medically. Some cats are persistent stone formers and approximately 35% of cats with calcium oxalate stones are hypercalcaemic.

Acute complete obstruction or severe partial obstruction results in potentially fatal post-renal azotaemia. Hydronephrosis develops following ureteric obstruction and, if the obstruction is not relieved, fibrosis and irreversible damage results. The sooner the obstruction is relieved, the less nephron damage occurs. Partial obstructions result in less severe damage compared with complete obstructions.

Often cats have bilateral ureteric obstruction at the time of presentation. When the initial ureter becomes obstructed, the glomerular filtration rate increases in the contralateral kidney and the cat may not show any clinical signs and may not be azotaemic. There is initial hydronephrosis on the affected side, but the kidney eventually shrinks and has significantly reduced function. If the contralateral kidney becomes similarly obstructed, severe post-renal azotaemia may develop and the cat may show clinical signs.

Presenting signsClinical signs associated with ureteric calculi can be vague and of variable severity. Signs of unilateral ureteric obstruction in the absence of chronic kidney disease may go unnoticed by the owners. Many cats present with a non-specific history of lethargy,

inappetence and recent or chronic weight loss. If the cat has concurrent significant kidney disease then signs may be more severe and can include polyuria, polydipsia, vomiting and generalized weakness. Cats can also be pyrexic if pyelonephritis is present. In addition, ureteric obstruction is painful and some cats react to palpation of the overlying spine or abdominal wall.

DiagnosisAbdominal palpation may reveal signs of pain over or around the kidneys. One kidney may appear to be enlarged (the obstructed side) while the other may appear small (atrophied following a previous episode of ureteric obstruction), giving rise to the big kidney, little kidney presentation. Such a finding warrants immediate investigation and/or renal imaging.

Serum biochemistry in affected cats can vary from being normal (e.g. in cats with a unilateral obstruction and without chronic kidney disease (CKD) to revealing signs of severe azotaemia, including raised urea, creatinine, phosphate and potassium. Urine specific gravity is often

BSAVA 2014 | companion SEPTEMBER 2014 | 15

common. Abdominal radiography is also useful, as the majority of feline ureteroliths are calcium oxalate and thus radiopaque (Figure 2). The sensitivity of ultrasonography for the detection of feline ureteroliths is 77%, that of abdominal radiography is 81%, and when the two modalities are used together they have a sensitivity of 90%.

If abdominal ultrasonography is equivocal and there is a high clinical suspicion of ureteric obstruction, other techniques, such as positive contrast antegrade pyelography, can be used. A long 22 G needle is directed into the renal pelvis under ultrasound or fluoroscopic guidance and the attached syringe and three-way tap can be used to obtain a urine sample for bacterial culture and sensitivity testing and then to inject iodinated contrast agents to highlight the affected ureter. More advanced imaging modalities, including computed tomography (CT), magnetic resonance imaging (MRI) and nuclear scintigraphy, have been described but are not usually required.

TreatmentMedical managementMost cases of ureteric obstruction benefit from a period of medical management, although this is only successful at fully resolving the ureteric obstruction in a

Figure 1: Ultrasonogram of a kidney with hydronephrosis secondary to ureteric obstruction

Figure 2: (A) Lateral and (B) ventrodorsal radiographs of a cat with multiple irregularly shaped and sized mineral opacities within the renal pelvis and left ureter

A

B

minority of cases (17% of cats). Cats that present with significant hyperkalaemia are usually best treated surgically after an initial 2448 hours of stabilization; those cats unresponsive to medical management may undergo surgery sooner.

Medical management includes analgesia (usually opioids), appropriate intravenous fluid therapy and pharmacological intervention. Multiple drugs (e.g. amlodipine, amitriptyline,

glucagon and diuretics such as mannitol) have been used with the aim of relieving ureteric spasm, encouraging ureteric dilation or increasing urine production. However, it must be stressed that evidence to support the use of these drugs is lacking and potential adverse effects in severely sick cats must be considered. Cats need to be closely monitored during this initial stabilization period and have their weight, hydration status, blood pressure,

14-18 How To.indd 15 18/08/2014 12:30

16 | companion SEPTEMBER 2014 | BSAVA 2014

How to manage feline ureteric obstruction

respiratory rate, electrolytes, creatinine and PCV checked regularly (at least daily). Renal imaging should be repeated at 4872 hours a decrease in renal pelvis dimensions together with resolution of the azotaemia would suggest resolution of the ureteric obstruction.

Other non-surgical techniques that can be used include extracorporeal shock wave lithotripsy, although this has met with mixed success in feline cases and is not widely used or available. Nephrostomy tubes can be placed and will rapidly resolve the azotaemia and decrease intra-ureteric/pelvic pressure but can be associated with complications, including urine leakage, dislodgement and infection. They are also very challenging to place percutaneously in cats and provide only short-term palliation, requiring the ureteric obstruction to be removed using other techniques.

Surgical managementTraditional techniquesSurgical removal of an obstructing ureterolith is achieved via a midline coeliotomy. Full exploration of the urinary tract is mandatory as multiple ureteroliths may be present. Once the obstruction has been localized a decision as to how to remove it must be made.

Proximal calculi can be flushed back to the renal pelvis by performing a cystotomy

and catheterizing the affected ureter. The calculi can then be removed via pyelotomy, which is technically easier and may be less likely to result in significant ureteral stenosis. Distal ureteric obstructions can be managed by transection of the affected portion (ureterectomy) and re-implantation of the remaining ureter into the apex of the bladder (neoureterocystostomy; Figure 3). This can be accomplished using either intra-vesicular (the bladder is incised and the ureteral mucosa is directly sutured to the bladder mucosa) or extra-vesicular (the ureter is dropped in to the bladder via a stab incision and sutured without performing a cystotomy) techniques. Both techniques require magnification and are technically challenging. Loss of ureteric length can create tension, but this can often be offset by caudal mobilization of the kidney (renal descensus) or cranial anchoring of the bladder apex (e.g. psoas cystopexy).

Other surgical options for mid-ureteric obstructions include ureterotomy (Figures 4 and 5) or resection and anastomosis. Ureteronephrectomy is rarely a viable option as >80% of cats are azotaemic at the time of presentation, implying dysfunction of the other kidney, thus as much renal function as possible needs to be preserved in these patients.

Complications may be seen in approximately 30% of cases and include oedema/inflammation at the

Figure 3: Close-up view of neoureterocystostomy being performed in a dog. Ureterectomy has been performed and the remaining dilated ureter has been pulled through an apical stab incision visualized via a separate cystotomy incision. The ureter has been catheterized

Figure 5: Ureterolith removed via ureterotomy

Figure 4: Intraoperative photograph of a feline ureterotomy being closed. A length of 2M polypropylene has been placed into the ureteric lumen to help preserve orientation during closure

ureterovesical junction, stenosis, urine leakage (uroabdomen) and persistent obstruction. Urine leakage is the most common complication and is seen in

BSAVA 2014 | companion SEPTEMBER 2014 | 17

Figure 6: Double pigtail polyurethane stent

Initially, a catheter is placed through the kidney parenchyma into the renal pelvis and a hydrophilic guidewire is passed though the catheter, down the ureter and into the bladder. The catheter is then removed and a dilator is passed over the guidewire. The dilator is subsequently removed and a stent is placed over the guidewire with one pigtail in the renal pelvis and the other in the bladder trigone (Figure 7). However, it is not always possible to place the stents passed the obstruction and in these cases ureterotomy or ureterectomy is often necessary; these cats are still at risk of uroabdomen postoperatively, so it is advisable to place a Jackson-Pratt abdominal drain. The drain allows for urine drainage during the period of postoperative diuresis where urine production can be >20 ml/kg/hr.

Stents can be challenging to place and surgery times can be prolonged. In addition, there is a high rate of dysuria because of the position of the pigtail in the trigone. Other complications include stent fracture, migration and encrustation leading to blockage.

Subcutaneous ureteric bypass (SUB) systemThis is an extra-anatomical device consisting of a pigtail nephrostomy tube and a cystostomy tube, which are connected via a subcutaneous access port (Figure 8).

Intraoperative fluoroscopy is needed at multiple stages during the procedure. The nephrostomy tube is placed first. A guidewire is placed in the renal pelvis via a catheter, which is then removed. The nephrostomy tube is placed over the guidewire and, once the correct position has been confirmed using fluoroscopy, the pigtail is locked, securing its position.

Figure 7: Postoperative lateral radiograph of a cat with bilateral ureteric stents

A

B

Figure 8: (A) Lateral and (B) ventrodorsal radiographs of a cat with bilateral SUB systems 1 year following placement. Note the two nephrostomy tubes that enter the subcutaneous port caudally and the single cystostomy tube that exits the port cranially

A Dacron cuff is glued to the renal capsule using sterile cyanoacrylate glue.

The cystostomy tube is placed in the bladder via a small stab incision and through a purse string suture and secured via sutures placed through the Dacron cuff to the bladder wall at the apex (Figure 9).

These two tubes are then passed through the body wall and connected to the subcutaneous port using sterile cyanoacrylate glue (Figure 10). The

system is checked for leakage via a contrast study; the contrast medium is injected using a Huber needle placed in the subcutaneous port. The Huber needle is the only needle compatible with the SUB system as it is non-coring and thus will prevent leakage when removed.

The SUB system is technically simpler to place than stents, with shorter surgery times and less severe dysuria noted. However, potential complications include

14-18 How To.indd 17 18/08/2014 12:30

18 | companion SEPTEMBER 2014 | BSAVA 2014

Figure 9: Intraoperative photograph showing a nephrostomy tube placed in the right kidney and a cystostomy tube

Figure 10: Intraoperative photograph of the subcutaneous portPicture courtesy of Zoe Halfacree

Figure 11: Lateral radiograph of the cat in Figure 8 undergoing a contrast study to ensure patency of the SUB system. Contrast medium is visible in both renal pelves and the bladder. Following relief of the obstruction, the right ureter has become unobstructed

urine leakage, tube kinking leading to obstruction, infection and encrustation. The SUB system should be checked every 36 months to ensure patency (Figure 11).

PrognosisThe main factor affecting outcome in these cats is the severity of the kidney disease as a result of the obstruction. One study found that cats with an International Renal Interest Society (IRIS) CKD stage of 1 or 2 had a good long term outcome and those with a score of 3 or 4 had a median life expectancy of 272 days. To date, no factors associated with survival have been identified and so it is impossible to ascertain the outcome of these cats prior to treatment.

ConclusionUreteric obstruction is a potentially life-threatening condition with a relatively poor prognosis in cats with variable renal function. There is no one ideal surgical option; however, currently, the SUB system may be the best solution in these cats, where appropriate facilities for its placement are available.

Higher resoluti on images and references are available online and in e-companion

MORE ONLINE

34 October 2014AVSTS/SAMSoc AUTUMN MEETINGThe Association of Veterinary Soft Tissue Surgeons is a satellite group of BSAVA. Members include specialist surgeons and general practitioners. In October AVSTS is running a joint scientific meeting with the Small Animal Medicine Society. The topic will be Organ Failure and the meeting will be held in the Queens Hotel in Chester. As always, this promises to be a thought-provoking and entertaining meeting with world-class speakers.

Visit www.avsts.org.uk for full details and to book online.Email avstsadmin@fsmail.net for more details.

Organ failureA medical and surgical approach

How to manage feline ureteric obstruction

14-18 How To.indd 18 18/08/2014 12:30