Technical and clinical outcomes of ureteral stenting in cats with benign ureteral obstruction: 69 cases (2006–2010)

Allyson C. Berent Department of Diagnostic Imaging and Interventional Radiology, The Animal Medical Center, 510 E 62nd St, New York, NY 10065.

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Chick W. Weisse Department of Diagnostic Imaging and Interventional Radiology, The Animal Medical Center, 510 E 62nd St, New York, NY 10065.

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Kimberly Todd Department of Clinical Studies, Matthew J. Ryan Veterinary Hospital, University of Pennsylvania, Philadelphia, PA 19104.

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Demetrius H. Bagley Department of Urology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107.

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Abstract

Objective—To evaluate the technical, short-term, and long-term outcomes in cats with benign ureteral obstructions treated by means of double-pigtail ureteral stent placement.

Design—Retrospective case series.

Animals—69 cats (79 ureters).

Procedures—The diagnosis of benign ureteral obstruction was made via abdominal ultrasonography, radiography, and ureteropyelography. Ureteral stent placement was attempted endoscopically, surgically, or both, with fluoroscopic guidance. The medical records were reviewed for pre-, intra-, and postoperative data; complications; and outcome.

Results—69 cats (79 ureters) had stent placement attempted for various causes: ureterolithiasis (56/79 [71%]), stricture (10/79 [13%]), both ureterolithiasis and stricture (12/79 [15%]), or a purulent plug (1/79 [1%]). Stent placement was successful in 75 of 79 ureters (95%). Median number of stones per ureter was 4 (range, 0 to > 50), and 67 of 79 (85%) had concurrent nephrolithiasis. Preoperative azotemia was present in 95% (66/69) of cats (median creatinine concentration, 5.3 mg/dL [range, 1.1 to 25.8 mg/dL]), and 71% (49/69) remained azotemic (median, 2.1 mg/dL [range, 1.0 to 11.8 mg/dL]) after successful surgery. Procedure-related, postoperative (< 7 days), short-term (7 to 30 days), and long-term (> 30 days) complications occurred in 8.7% (6/69; 7/79 ureters), 9.1% (6/66), 9.8% (6/61), and 33% (20/60) of cats, respectively; most of these complications were minor and associated with intermittent dysuria or the need for ureteral stent exchange. The perioperative mortality rate was 7.5% (5/69), and no deaths were procedure related. The median survival time was 498 days (range, 2 to > 1,278 days). For patients with a renal cause of death, median survival time was > 1,262 days, with only 14 of 66 cats (21%) dying of chronic kidney disease. Nineteen (27%) cats needed a stent exchange (stricture in-growth [n = 10], migration [4], ureteritis [2], dysuria [2], pyelonephritis [1], or reflux [1]). No patient died of the procedure or recurrent ureteral obstruction.

Conclusions and Clinical Relevance—Results of the present study indicated that ureteral stenting is an effective treatment for benign ureteral obstructions in cats regardless of obstructive location, cause, or stone number. The perioperative morbidity and mortality rates were lower than those reported with traditional ureteral surgery. The short- and long-term complications were typically minor but may necessitate stent exchange or use of an alternative device, particularly with ureteral strictures. The prognosis for feline ureteral obstructions after ureteral stenting could be considered good when the procedure is performed by trained specialists.

Abstract

Objective—To evaluate the technical, short-term, and long-term outcomes in cats with benign ureteral obstructions treated by means of double-pigtail ureteral stent placement.

Design—Retrospective case series.

Animals—69 cats (79 ureters).

Procedures—The diagnosis of benign ureteral obstruction was made via abdominal ultrasonography, radiography, and ureteropyelography. Ureteral stent placement was attempted endoscopically, surgically, or both, with fluoroscopic guidance. The medical records were reviewed for pre-, intra-, and postoperative data; complications; and outcome.

Results—69 cats (79 ureters) had stent placement attempted for various causes: ureterolithiasis (56/79 [71%]), stricture (10/79 [13%]), both ureterolithiasis and stricture (12/79 [15%]), or a purulent plug (1/79 [1%]). Stent placement was successful in 75 of 79 ureters (95%). Median number of stones per ureter was 4 (range, 0 to > 50), and 67 of 79 (85%) had concurrent nephrolithiasis. Preoperative azotemia was present in 95% (66/69) of cats (median creatinine concentration, 5.3 mg/dL [range, 1.1 to 25.8 mg/dL]), and 71% (49/69) remained azotemic (median, 2.1 mg/dL [range, 1.0 to 11.8 mg/dL]) after successful surgery. Procedure-related, postoperative (< 7 days), short-term (7 to 30 days), and long-term (> 30 days) complications occurred in 8.7% (6/69; 7/79 ureters), 9.1% (6/66), 9.8% (6/61), and 33% (20/60) of cats, respectively; most of these complications were minor and associated with intermittent dysuria or the need for ureteral stent exchange. The perioperative mortality rate was 7.5% (5/69), and no deaths were procedure related. The median survival time was 498 days (range, 2 to > 1,278 days). For patients with a renal cause of death, median survival time was > 1,262 days, with only 14 of 66 cats (21%) dying of chronic kidney disease. Nineteen (27%) cats needed a stent exchange (stricture in-growth [n = 10], migration [4], ureteritis [2], dysuria [2], pyelonephritis [1], or reflux [1]). No patient died of the procedure or recurrent ureteral obstruction.

Conclusions and Clinical Relevance—Results of the present study indicated that ureteral stenting is an effective treatment for benign ureteral obstructions in cats regardless of obstructive location, cause, or stone number. The perioperative morbidity and mortality rates were lower than those reported with traditional ureteral surgery. The short- and long-term complications were typically minor but may necessitate stent exchange or use of an alternative device, particularly with ureteral strictures. The prognosis for feline ureteral obstructions after ureteral stenting could be considered good when the procedure is performed by trained specialists.

Ureterolithiasis is the most common cause of ureteral obstruction in both canine and feline patients,1–5 although trigonal neoplasia,6,7 ureteral strictures (congenital or acquired),5,8,a–c and solidified blood clots and calculi9 have also been reported. The increasing incidence of ureteral obstructions in small animal patients, combined with the invasiveness and morbidity associated with traditional open surgical techniques,2,10 makes the use of newer interventional options appealing. Greater than 98% of ureteroliths in feline patients have been documented to be composed of calcium oxalate material.1,2,11 These types of stones will not dissolve with medical treatment and either need to pass spontaneously, be removed, or be bypassed to permit urine drainage and prevent renal damage. Once medical management fails, partial obstructions are often left untreated in many practices because of the risk-benefit ratio of attempted surgical removal.

A study12 of normal dogs after a ureteral obstruction was created showed that renal blood flow diminishes to 40% of normal over the first 24 hours and to 20% of normal by 2 weeks. Furthermore, in another study of healthy dogs,13 the excessive back pressure was transmitted to the entire nephron, and a decrease in glomerular filtration rate occurred via concurrent vasoactive mediator release, leukocyte influx, and subsequent fibrosis. These and additional studies14–16 of experimental animals and human patients demonstrated that the longer the duration of ureteral obstruction, the more severe and irreversible the damage. In a study of dogs,13 after 7 days of obstruction, the glomerular filtration rate was permanently diminished by a mean of 35%, and when the obstruction lasted for 14 days, the glomerular filtration rate was diminished by 54%. These data were obtained from an experimental study13 in dogs with complete acute obstruction, without preexisting azotemia, chronic interstitial nephritis, or chronic obstruction. A worse outcome might be expected in patients that are azotemic and have exhausted their compensatory hypertrophy mechanisms prior to the obstruction. It was also shown13,15,16 to take > 4 months for residual renal function to return after an obstruction. Because many feline patients with ureteral obstructions have concurrent renal compromise1,2,4,5 and a history of chronic kidney disease, aggressive and early treatment is recommended to improve overall renal function and the likelihood of the best outcome.

Studies2,17 suggest that surgical treatment is indicated when medical management fails. In 1 study of cats,2 there was an 8% documented and 13% presumptive stone passage rate, with a 33% mortality rate prior to discharge with medical management alone. This is compared with a 30% morbidity rate and 21% mortality rate after ureterotomy, ureteral reimplantation, ureteronephrectomy, or renal transplantation.2 The leading cause of perioperative complications was urinary leakage or ureteral re-obstruction due to a stricture at the surgical site, persistent ureteral calculi, or concurrent nephroliths that became ureterolith induced obstructions. Additionally, 40% of patients in that study2 had a ureteral obstruction recurrence, 86% of which had evidence of nephroliths at the time of the first surgery.2 Because of a high perioperative morbidity and mortality rate for feline patients undergoing medical or traditional surgical management for ureteral obstructions, other treatment modalities have been investigated.4,5,8,a–c

In human patients, the development of and improvements in ureteroscopy, ureteral stenting, extracorporeal shockwave lithotripsy, laser lithotripsy, laparoscopy, and percutaneous nephroureterolithotomy have nearly eradicated the need for open ureteral surgery for stone disease, strictures, trauma, neoplasia, and congenital anomalies.18–27 Ureteroscopy, shockwave lithotripsy, and laparoscopic treatment of ureteral obstructions are not typically possible in feline patients because of the narrow diameter of the ureter in cats (0.3 to 0.4 mm).17,28,29 This anatomic limitation, and a report27 in human patients that ureteral stents cause passive ureteral dilation over a few days to weeks, have been the basis for investigation into ureteral stenting for the treatment of ureteral obstructions in feline patients.4,5,8,a,c

Ureteral stenting was first introduced in 1967 for evaluation of human patients with malignant ureteral obstructions.23 Ureteral stents are still widely used to treat both benign and malignant obstructive disease in people, and this is now considered the standard of care in many clinical situations for either temporary or definitive treatment. The goals of ureteral stenting are to bypass a ureteral obstruction and stabilize concurrent azotemia, to allow passive ureteral dilation for improved urine flow, to manage edema following ureteroscopy or surgery, to improve the success of extracorporeal shockwave lithotripsy, and to aid in spontaneous stone passage.25,26 Ureteral stent placement in veterinary medicine was first reported in 2007 in canine and feline patients for the treatment of both benign and malignant disease.a Since that time, few reports4,5,8,c on their use in the management of canine and feline ureteral disease have been published. The objective of the study reported here was to describe the ureteral stenting procedure in feline patients in detail as well as the outcome for use of various ureteral stents for the treatment of a relatively large number of feline patients with naturally occurring benign ureteral obstructions.

Materials and Methods

Selection of cases—Feline patients were included if they had a diagnosis of a benign ureteral obstruction in which a ureteral stent procedure was attempted by 1 of the 2 authors (ACB or CWW) at either the Animal Medical Center New York or the Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania between October 2006 and December 2010. The diagnosis of a benign ureteral obstruction was made on the basis of results of 3 imaging modalities: abdominal ultrasonography, with a finding of renal pelvis dilation with associated hydroureter to the level of an obstructive ureteral lesion; abdominal radiography (to identify renal, ureteral, or bladder calculi); and ureteropyelography (either antegrade or retrograde). The ureteropyelography was typically performed immediately prior to ureteral stent placement. Patients were serially enrolled in this study. Case animals were included only if owner consent for ureteral stent placement was obtained, if placement of a double-pigtail ureteral stent was attempted either surgically or endoscopically (and, if endoscopy failed, then stent placement was converted surgically), if the obstruction was due to benign disease (ureterolithiasis, ureteral stricture, dried solidified blood stones, or inspissated purulent material), and if details were available for review in the medical record. The medical record review included the following: preoperative history, diagnostic imaging, biochemical parameters, surgical report, all perioperative (immediate pre-, intra-, and postoperative [< 1 week]) and short- and long-term postoperative complications, and both short- and long-term outcomes (clinical features and results of repeat biochemical testing). Ultimate outcome was necessary for inclusion, and all patients, if still alive, needed > 6 months of follow-up to be included. Cases were excluded if owners were not willing to consent to surgical intervention if endoscopic stent placement failed and if stents were placed for malignant ureteral obstructions, for ureteral fibrosis after renal transplantation, or for trauma or postsurgical healing.

All feline patients were separated into 2 groups on the basis of stent type used. Group 1 included patients for which all types of ureteral stentsd–f were used prior to the development of the commercially available feline ureteral stent. Group 2 included patients for which a commercially available double-pigtail feline ureteral stentg was used.

Historical and laboratory data—Data regarding signalment, previous medical and surgical history, duration of illness, previous history of chronic kidney disease, previous need for dialysis or a nephrostomy tube, previous diagnostic imaging, biochemical information, microbiological information, clinical signs, physical examination findings, and preoperative blood pressure were recorded. All cats had a preoperative CBC, serum biochemical profile, urinalysis, and bacteriologic culture of urine with antimicrobial susceptibility testing. Any patient with an active UTI was administered antimicrobial treatment for a minimum of 24 hours prior to ureteral stent placement when possible, and this treatment continued for a minimum of 6 weeks.

Imaging—All patients underwent abdominal ultrasonography (at a minimum, focused urinary tract ultrasonography), abdominal radiography, and, if a heart murmur or arrhythmia was present, thoracic radiography prior to stent placement. If indicated, echocardiography was also performed prior to anesthesia. Prior to stent placement, ureteropyelography was performed. This was done as either antegrade pyelography (via ultrasonography or surgical access and visualized with the aid of fluoroscopic or radiographic imaging) or retrograde ureteropyelography by means of fluoroscopy with either cystoscopic or surgical guidance for UVJ catheterization to confirm the presence of a ureteral obstruction. A ureteral obstruction was diagnosed by means of ultrasound guidance with the presence of a combination of hydronephrosis and associated hydroureter to an area of the ureter that was either clearly obstructive (ie, stone) or had an abrupt taper (ie, stricture or blood stones). Additionally, all cases had a ureteropyelogram performed demonstrating a dilated renal pelvis and ureter, proximal to an obstructive lesion.

Data collected included location of ureteral calculi, number of ureteral calculi, presence and number of nephroliths, size of ureteral calculi, dimensions of the ureteral and renal pelvic dilation, and presence of bladder stones. The renal pelvis measurement was based on the diameter obtained on a traditional transverse ultrasonographic image that was available for review. Obstruction location was classified as at the UPJ, in the proximal ureter (< 4 cm beyond the UPJ), in the midureter (4 to 8 cm beyond the UPJ), in the distal ureter (> 8 cm beyond the UPJ), or at multiple locations.

Grading of ureteral obstruction severity—The ureteral obstruction severity was graded on the basis of results of diagnostic imaging and the perceived surgical difficulty of performing a routine ureterotomy or ureteral reimplantation on a scale of 1 through 5 (1 = requiring 1 ureterotomy or a ureteral reimplantation; 2 = 2 ureterotomy procedures or reimplantation with renal descensus and nephrocystopexy; 3 = 3 or more ureterotomy procedures with stone[s] too proximal for renal descensus or reimplantation; 4 = need for a pelvicvesicular anastomosis; 5 = a proximal ureteral stricture requiring a ureteral resection and anastomosis with or without psoas nephrocystopexy).

Medical management—When possible, all patients were medically managed for a minimum of 24 hours prior to considering ureteral stent placement in an attempt to achieve successful spontaneous stone passage. This was not attempted in cases with severe hyperkalemia (> 7 mEq/L), anuria, or overhydration, where medical management alone was contraindicated. Medical management consisted of various modalities, including IV fluid therapy, α-adrenergic blockade with prazosin (0.25 to 0.5 mg/cat, PO, q 12 h), mannitol treatment (0.25 to 0.5 g/kg [0.125 to 0.25 g/lb] bolus over 30 minutes, then 1 mg/kg/min [0.5 mg/lb/min], IV, continuous rate infusion for 24 hours), or amitriptyline treatment (0.5 to 1.0 mg/kg, PO, q 24 h). Appropriate antimicrobial treatment, H2-receptor antagonists, phosphate binders, and amlodipine were also used when necessary, and dosages were chosen by the treating clinician. Depending on patient status, intermittent hemodialysis, peritoneal dialysis, and preoperative nephrostomy tube placement were also performed when necessary. For nephrostomy tube placement, a 5F locking-loop pigtail catheterh was used via either a percutaneous or laparotomy approach. This was typically accomplished following the modified Seldinger technique and fluoroscopic guidance, which has been described previously.30 Patients were monitored via serial ultrasonography, serial survey abdominal radiography, urine output quantification, and monitoring of serum BUN, creatinine, blood gas, and electrolyte concentrations.

Ureteral stenting procedure—The typical anesthesia protocol included premedication with oxymorphone (0.1 mg/kg [0.045 mg/lb], IM) and glycopyrrolate (0.01 mg/kg [0.005 mg/lb], IM); induction with propofol (3 mg/kg [1.36 mg/lb], IV) or etomidate (1 to 2 mg/kg [0.45 to 0.9 mg/lb], IV) and midazolam (0.25 to 0.5 mg/kg [0.11 to 0.22 mg/lb], IV); and maintenance with a fentanyl constant rate infusion (0.35 to 0.7 μg/kg/min [0.16 to 0.32 μg/lb/min], IV) and inhalant anesthesia. If hypotension occurred during anesthesia, dopamine was administered at a dose of 5 to 12 μg/kg/min (2.2 to 5.45 μg/lb/min) as a constant rate infusion. Once under general anesthesia, the patient was positioned in dorsal recumbency. The abdomen and vulva or prepuce were clipped of hair and aseptically prepared. The entire abdomen and vulva or prepuce were draped. If the patient was not currently receiving antimicrobial treatment, perioperative cefazolin was administered every 2 hours (22 mg/kg [10 mg/lb], IV) throughout anesthesia. All patients had a double-pigtail ureteral stent placed of various types. The ureteral stents used in this study were a double-pigtail polyurethane-type catheter (Figure 1). The stent travels inside the entire ureteral lumen with a proximal pigtail loop curling inside the renal pelvis, the shaft inside the entire ureteral lumen, and the distal pigtail loop curling inside the urinary bladder. The pigtail loops are designed to help to prevent stent migration.

Figure 1—
Figure 1—

Photographs of a feline-specific 2.5F multifenestrated double-pigtail ureteral stent,g used for cats undergoing ureteral stenting for benign ureteral obstruction. This stent was used to treat patients enrolled from mid-2009 until the completion of the study at the end of 2010. A—There are 2 loops: the proximal loop and the distal loop (black band is above the distal loop). B—Photograph of the proximal loop of the ureteral stent in panel A showing the tapered end and multiple fenestrations. C—Photograph of the dilator (pusher catheter) used to place the ureteral stent.

Citation: Journal of the American Veterinary Medical Association 244, 5; 10.2460/javma.244.5.559

Endoscopic stent placement with a 1.9-mm rigid cystoscope,i along with fluoroscopy,j,k was attempted in some female cats. This was not possible in male cats. Once the appropriate UVJ was identified, a 0.018-inch angle-tipped hydrophilic guide wirel was advanced into the distal ureter. An open-ended ureteral catheter (3F)m or a ureteral dilation catheter (0.034-inch)n was advanced over the wire into the distal ureter. The guide wire was then removed, and retrograde ureteropyelography (a 1:1 dilution of contrast mediumo and sterile saline [0.9% NaCl] solution) was performed with the aid of fluoroscopic guidance (typically a volume of 1 to 2 mL). The contrast ureteropyelography aided in the identification of lesions, stones, or other filling defects in the ureter, the tortuosity of the obstructed portion of the ureter, and the location of the renal pelvis (Figure 2). This helped to outline the path of the ureter for wire passage around the obstructive lesions and into the renal pelvis. The wire was reintroduced into the ureteral catheter and advanced into the renal pelvis. The wire was then curled inside the renal pelvis, and the ureteral catheter was advanced over the wire to the renal pelvis. This catheter was used to measure the ureteral length. A sample of urine was routinely obtained for microbiological analysis. Then, the ureteral catheter was removed over the guide wire. Next, the ureteral stent was advanced over the wire, with one curl remaining inside the renal pelvis in front of the obstruction and the other curl pushed through the endoscope into the urinary bladder with the distal portion of the ureteral pusher catheter.m,n

Figure 2—
Figure 2—

Ureteral stent placement in an 8-year-old spayed female domestic shorthair cat undergoing treatment for a right-sided ureteral obstruction. This procedure was performed in a retrograde manner with cystoscopic and fluoroscopic guidance. A—Fluoroscopic image with the patient in dorsal recumbency showing a guide wire (black arrows) in the distal-mid ureter that was placed in a retrograde manner guided by cystoscopy and fluoroscopy. B—Fluoroscopic image of the ureteral dilator (yellow arrows) that was placed over the guide wire and a retrograde ureteropyelogram being performed documenting the stones (red arrow) and hydroureter with hydronephrosis (red arrow head). C—Fluoroscopic image obtained when the guide wire (black arrow) was replaced through the ureteral dilator (yellow arrow) and was guided into the renal pelvis. D—Fluoroscopic image obtained as the guide wire was advanced and curled inside the renal pelvis and the stent was then being passed up the ureter, over the guide wire, and into the renal pelvis. E—Endoscopic image of the bladder with the cat positioned in dorsal recumbency as the guide wire was advanced into the UVJ on the right side. F—Endoscopic image obtained as the ureteral dilator was being advanced over the guide wire, up the UVJ, and into the ureter, guided through the endoscope. G—A lateral radiograph of the abdomen after the stent was in an appropriate position traveling from the renal pelvis (proximal loop) down the ureter (shaft) and into the urinary bladder (distal loop).

Citation: Journal of the American Veterinary Medical Association 244, 5; 10.2460/javma.244.5.559

Surgical approach—The surgical technique was performed via a ventral midline laparotomy. This was performed 1 of 3 ways: antegrade via pyelocentesis through a nephrostomy needle and catheter, retrograde through the UVJ, or through a ureterotomy incision. The antegrade technique (Figure 3) was the preferred approach and required nephrostomy needle access with a 22-gauge over-the-needle catheter into the renal pelvis through the greater curvature of the kidney, aiming toward the UPJ. A pyelocentesis and antegrade pyelogram were then performed with fluoroscopic guidance. The urine obtained was routinely evaluated, including bacteriologic culture and antimicrobial susceptibility testing. The 0.018-inch guide wirel was then advanced down the ureter guided by the ureteropyelogram, around or through the obstructive lesion, and into the urinary bladder. With a small caudodorsal cystotomy (2 to 3 mm), the guide wire was advanced out of the incision to gain through-and-through access (flossed). If the wire was difficult to pass around the stone or through the stricture, particularly when the proximal ureter was very tortuous, then dissection of the periureteral tissue was done to straighten out the ureter and facilitate passage. Once through-and-through access was obtained for the wire, the ureteral dilatorn was advanced over the guide wire, in an antegrade manner from the kidney to the urinary bladder, through the UVJ, and out of the cystotomy incision. Next, the ureteral stentd–g was advanced over the guide wire in an antegrade manner, following the ureteral dilator (piggyback) until it was seen to exit the UVJ into the urinary bladder through the cystotomy incision. Once through-and-through access was gained for the stent, the guide wire was removed from the lumen of the stent and reversed so that the soft, angled end was advanced in a retrograde manner up the stent. The soft end of the wire was then advanced out one of the side holes (Figure 3), in the proximal loop to maintain through-and-through access. This would allow a proximal curl to form once pulled into the kidney. The stent was then pulled caudally from the bladder side until the proximal end of the stent was pulled into the dilated renal pelvis, maintaining guide wire access through and through, while monitoring with fluoroscopy. The proximal end of the guide wire, still externalized, was then pulled cranially to aid in curling the proximal loop in the renal pelvis, and then the guide wire was removed, ensuring the proximal loop remained inside the renal pelvis.

Figure 3—
Figure 3—

Ureteral stent placement in a 12-year-old castrated male domestic shorthair cat with a right-sided ureteral obstruction performed with surgical assistance in an antegrade manner via nephrostomy access. A—Patient in dorsal recumbency during ventral midline laparotomy. Nephrostomy access was obtained in the right renal pelvis through the greater curvature under fluoroscopic guidance. A sample of urine was taken, and contrast was then infused for an antegrade pyeloureterogram. B—Fluoroscopic image of the right-sided antegrade pyeloureterogram documenting a proximal ureteral obstruction secondary to a ureteral stricture. C—The 0.018-inch guide wire (black arrow) is being advanced down the lumen of the 22-gauge catheter, into the renal pelvis, and down the ureter with fluoroscopic guidance. D—The guide wire is seen traveling down the ureter (black arrow) to the urinary bladder. E—A small dorsal cystotomy was performed to obtain through-and-through guide wire access (black arrow). F—The ureteral stent passed from the kidney, down the ureter, and into the bladder. This image shows the guide wire (black arrow) coming out one of the side holes of the stent loop to facilitate appropriate proximal loop positioning in the renal pelvis. G—A fluoroscopic image while the ureteral stent was pulled into the renal pelvis, documenting proper positioning of the proximal loop. H—A ventrodorsal radiograph taken after surgery from another patient with multiple ureteroliths causing the obstruction, showing the ureteral stent as it traveled from the renal pelvis, next to the nephroliths and ureteroliths, down the entire ureter, and into the urinary bladder.

Citation: Journal of the American Veterinary Medical Association 244, 5; 10.2460/javma.244.5.559

Uncommonly, a ureterotomy was performed if the guide wire was not able to be passed around the obstructive stone. When necessary, the wire and stent were placed through the ureterotomy site in an antegrade manner into the urinary bladder. Once this was achieved, the wire was turned around so the angled floppy end was leading and passed up the stent, within the ureter, and into the renal pelvis. The stent was then advanced over the wire to the renal pelvis. The ureterotomy was then closed over the stent under magnification using 6–0 or 8–0 polyglactin suturep in a simple interrupted pattern.

The retrograde surgical technique was performed early in the course of the study but was found to be the most traumatic of the 3 approaches and rarely necessary. This is the same procedure as described for the endoscopic approach except that access to the UVJ was obtained surgically by use of the guide wire under magnification. This required a caudal ventral cystotomy and proximal urethrotomy because the location of the feline ureteral papilla is on the caudal aspect of the trigone inside the proximal urethra. All surgical procedures in which a cystotomy was performed were closed with 4–0 or 5–0 monocryl suture materialq in a simple interrupted or cruciate pattern.

All procedure times were recorded. After the stents were placed, a final ureteropyelogram was performed to confirm patency of the ureter and stent and to monitor for any ureteral leakage. If a ureterotomy was concurrently performed, a closed suction drainr was typically placed in the abdomen for 24 to 48 hours. In the rare instances in which drainage was of concern because of periureteral edema, a locking-loop nephrostomy catheterh was placed. All laparotomy incisions were routinely closed in 3 layers. A urethral catheters with a closed urinary collection system was placed in patients where monitoring urine output was considered desirable. An esophagostomy tubet was routinely inserted after surgery to aid in enteral fluid therapy and maintain nutrition after surgery.

Periprocedural data and management—All patients were carefully monitored for hydration status on the basis of central venous pressures, serial body weight, urine output quantification, biochemical and electrolyte concentrations, acid-base status, total solids concentration, and PCV. If an externalized urethral catheter was not in place and previously instituted antimicrobial treatment was not being used for a documented infection, antimicrobial treatment (marbofloxacin, 2.75 to 5.5 mg/kg [1.25 to 2.5 mg/lb], PO, q 24 h) was given and continued for 2 weeks. Pain control was according to clinician preference. Data were recorded for the highest urine output, IV fluid rate, enteral fluid rate, volume of fluid produced from the drain, and documentation of a uroabdomen on the basis of paired serum and peritoneal fluid creatinine and potassium concentrations within the first 24 hours. The need for any blood product transfusion or diuretic use was recorded. When used, the mannitol dosage was 0.25 to 0.5 g/kg (0.125 to 0.25 g/lb) IV given over 30 minutes, then 1 mg/kg/min, IV, as a continuous rate infusion for 12 to 24 hours.

Postprocedural data—Biochemical data (BUN, creatinine, phosphorus, potassium, sodium, total calcium, ionized calcium, and bicarbonate concentrations), PCV, and total solids concentration were recorded at approximately 24 hours after stent placement. The lowest BUN and creatinine concentrations during hospitalization and all biochemical data available prior to discharge were recorded. Results of bacteriologic culture of urine prior to urinary catheter removal, transverse renal pelvis ultrasonography dimension measurements, and length of hospital stay prior to discharge were recorded.

Complications—Any minor or major procedural, postoperative (< 1 week), short-term (1 week to ≤ 1 month), and long-term (> 1 month) complication was recorded. Major complications were considered those that required another surgical intervention for resolution, and minor complications were those that were able to be resolved with medical management alone or did not require treatment.

Follow-up—Patients that survived to discharge had follow-up data recorded, including biochemical data, systolic arterial blood pressure, urine protein-to-creatinine ratio, body weight, and results of CBC, urinalysis, bacteriologic culture of urine, abdominal radiography, and urinary tract ultrasonography. These data were typically recommended to be obtained serially at 2 weeks, 6 weeks, 3 months, 6 months, 9 months, 12 months, and then every 3 to 6 months thereafter. If calcium oxalate stones were documented on the basis of results of stone analysis or suspected on the basis of negative results of urine culture and a low urine pH with highly radiopaque stones, potassium citrate supplementation (75 mg/kg [34 mg/lb], PO, q 12 h) was recommended long-term and the urine pH and serum potassium concentration were monitored. Patients that were persistently azotemic were recommended a long-term prescription renal diet, and those with a creatinine concentration in the normal range were recommended a stone-neutralizing prescription diet. Patients with serum phosphorus concentrations > 5 mg/dL were started on enteral aluminum hydroxide (90 mg/kg/d [41 mg/lb/d] mixed with food). Long-term medical management using diet, potassium citrate, and phosphate binders for the treatment of concurrent renal azotemia was encouraged when possible. Owners or referring veterinarians were contacted at study conclusion for a final update, and if the patient died, the cause of death was recorded when available and categorized as ureteral, renal, likely renal or ureteral, unlikely renal or ureteral, not renal or ureteral, or unknown.

Survival—Patient survival was characterized as survival to hospital discharge, 1 month, 6 months, 12 months, and > 24 months. Patient survival was categorized as total patient survival, survival separated according to IRIS stage at 3 months after surgery, and patients that died of ureteral or renal causes.

Statistical analysis—Cats were grouped according to which type of stent was placed (group 1 vs group 2). Cats treated with the earlier stent models were examined in the earlier study period (group 1; before mid-2009), and those treated with the specially designed feline ureteral stent (group 2) were examined in the later study period (from mid-2009 through study completion in December 2010).

Descriptive statistics, including frequency (%) for categorical variables and medians and ranges for continuous variables, were calculated for the overall sample. Outcomes of interest included stent exchange (yes vs no), straining short term (≤ 1 month; yes vs no), and straining long term (>1 month; yes vs no). The following univariate analyses were performed. The χ2 or Fisher exact test, as deemed appropriate, was used to determine the association between stent exchange (yes vs no) and the subsequent categorical variables: stricture, surgical approach, side, UTI prior to surgery, UTI after surgery, and stone location. The χ2 or Fisher exact test, as deemed appropriate, was used to determine the association between straining short term (yes vs no) and the subsequent categorical variables: history of UTI prior to and after stenting, sex, stent type, affected side, stent group and stent size, and surgical approach (retrograde vs antegrade). The Mann-Whitney test was used to compare those cats that had straining short term versus those that did not for the continuous variables of stent length and stent length in bladder. The same univariate analyses that were performed for straining short term were also performed for straining long term.

Overall survival time (time until death due to any cause) and renal survival time (time until death due to renal failure or urinary clinical signs only) for the cats were determined by computation of Kaplan-Meier product limit curves. Median survival times were reported with their corresponding 95% confidence intervals on the basis of the formula of Greenwood31 to calculate the SE. In cases where death had not yet occurred, the number of days until last follow-up was used to calculate survival time, and the case was considered censored. Univariate analyses of different categorical groups (eg, creatinine concentrations [categorized by stage of chronic kidney disease] or affected side) was accomplished by the same standard methods of survival analysis, where group was the stratification variable. These groups were compared by means of the log-rank test. The MSTs for each group were obtained from the Kaplan-Meier product-limit estimates, and their corresponding 95% confidence intervals were also computed. The association of each of the continuous variables (ie, blood work abnormalities before and after) with the survival distribution was tested in a univariate Cox proportional hazards regression model. Because of the small sample size in this study, multivariate models were not constructed.

Results were considered significant at P < 0.05, unless otherwise specified. All analyses were conducted with statistical software.u

Results

Selection of cases—Eighty feline patients with 91 obstructed ureters were initially evaluated in this study. Eleven cats (12 ureters) were excluded: 6 owners refused open surgery when endoscopy failed, 2 cats had bilateral obstructions as a result of transitional cell carcinoma, 1 cat had a ureteral obstruction after renal transplantation and ureteral allograft fibrosis, 1 cat had a stent placed to aid in ureteral anastomosis healing, and 1 cat had an incomplete medical record. There were 69 cats (79 ureters) that were then included and evaluated in detail. Sixty-six of 69 (96%) cats and 75 of 79 ureters (95%) had successful ureteral stent placement, with 4 stent placement failures. Failures were all a result of an inability to pass the stent through the undilated portion of the ureter distal to the obstruction. Five ureters required 2 surgical attempts at stent placement, all of which were in group 1. The initial preoperative and operative data include all 69 cats (79 ureters), and the follow-up data only include the 66 cats (75 ureters) that had a ureteral stent placed. Complication evaluation was based on the number of cats alive during the complication period being evaluated (procedure related postoperative, short term, and long term as defined previously).

Group 1d–f included 22 of 75 (29%) feline ureters that had a prototype or human pediatric stent used, and group 2g included 53 of 75 (70.6%) ureters that had the specially designed feline ureteral stent. All failures of stent placement were in group 1, which was prior to the availability of the smaller feline ureteral stentg and feline ureteral dilator.n In group 1 (n = 22 ureters), 18 of 22 (82%) had the 3F pediatric multifenestrated stent placed,e 2 of 22 (9%) the 3F nonfenestrated stent,d and 2 of 22 (9%) had a 1.9F nonfenestrated early prototype stentf placed. Group 2 (n = 53 ureters) included the specially designed feline ureteral stent,g which was available in 2 durometers (soft stent and stiff stent; Figure 1). The stiff stent allowed for easier placement in very narrow ureters when necessary. In group 2, 10 of 53 (19%) ureters had a stiff stent, and 43 of 53 (81%) had a soft stent. Forty-seven of 53 (89%) were 2.5F in diameter, 5 (9%) were 3.7F in diameter, and 1 (2%) was 4.7F in diameter. Of the 2.5F stents that were used, 13 of 47 (28%) were 12 cm long, 26 (55%) were 14 cm long, and 8 (17%) were 16 cm long.

Historical and clinical data—Thirty-nine of the 69 cats were spayed females, and 30 were neutered males. There were 48 domestic shorthair cats, 6 domestic longhair cats, and 15 purebred cats, including 4 Maine Coon, 3 British Shorthair, 2 Siamese, 2 Himalayan, 1 Scottish fold, 1 Bengal, 1 Persian, and 1 Norwegian Forest Cat. Median body weight was 4.34 kg (range, 2.2 to 10.1 kg). Median age at the time of the procedure was 8.3 years (range, 2.5 to 16 years). Past pertinent history included a previous episode of an ipsilateral ureteral obstruction in 16 of 69 (23%) cats, which were treated in various ways: ureterotomy or reimplantation (n = 11), medical management (2), and hemodialysis (3). Previous management for contralateral ureteral obstruction was reported in 3 of 69 cats, including ureterotomy (n = 2) and a ureteronephrectomy (1). Additionally, one cat had concurrent renal agenesis, and another cat had a history of ureteronephrectomy as a renal transplant donor. Prior to stent placement, there was a history of known azotemia in 38 of 69 cats (55%; range, 2 to 72 months) and a previous cystotomy for bladder stones in 7 of 69 (10%). Other history included chronic hematuria (suspected idiopathic renal hematuria) in 3 of 69 (4.3%), history of perinephric pseudocysts in 3 (4.3%), hypercalcemia of unknown cause in 3 (4.3%), known heart disease in 2 (3%), diabetes mellitus in 2 (3%), chronic pancreatitis in 2 (3%), feline inflammatory airway disease in 2 (3%), history of inflammatory bowel disease in 2 (3%), and a history of hyperthyroidism in 1 (1.4%).

Other relevant preoperative historical data included a decreased appetite (60/69 [87%]), chronic weight loss (40/69 [58%]), vomiting (33/69 [48%]), polyuria and polydipsia (17/69 [25%]), stranguria (17/69 [25%]), hematuria (11/69 [16%]), oliguria or anuria (11/69 [16%]), or diarrhea (7/69 [10%]). Thirty-four (34/69 [49%]) cats had a documented duration of their ureteral obstruction (median, 60 days; range, 15 to 1,800 days), and 7 of 69 (10%) patients received dialysis treatment (intermittent hemodialysis [n = 5] or peritoneal dialysis [2]) immediately prior to surgery. On physical examination, an enlarged kidney size was palpated in 18 of 79 (23%) obstructed kidneys, and a small kidney size was palpated in 20 of 79 (25%). Body condition score was assessed on a scale of 1 to 9, and the median score was 4.0. A heart murmur was detected in 33 of 69 (48%) cats. The median systolic arterial blood pressure at initial evaluation was 145 mm Hg (range, 90 to 190 mm Hg; reference range, 120 to 150 mm Hg).

Clinicopathologic and laboratory data—On initial evaluation, the median PCV was 32% (range, 19% to 48%; reference range, 29% to 45%), and total solids concentration was 7.2 g/dL (range, 6.0 to 9.1 g/dL; reference range, 5.9 to 8.5 g/dL). Twenty-eight of 69 (41%) cats were anemic at the time of admission.

The median BUN concentration was 66 mg/dL (range, 20 to 231 mg/dL; reference range, 15 to 34 mg/dL), and creatinine concentration was 5.3 mg/dL (range, 1.1 to 25.8 mg/dL; reference range, 0.8 to 1.9 mg/dL), with 66 of 69 (95%) cats being azotemic at the time of initial evaluation. The preoperative sodium concentration was 151 mEq/L (range, 133 to 162 mEq/L; reference range, 145 to 158 mEq/L), potassium concentration was 4.5 mEq/L (range, 2.9 to 8.6 mEq/L; reference range, 3.4 to 5.6 mEq/L), phosphorus concentration was 5.2 mg/dL (range, 3.4 to 18.2 mg/dL; reference range, 2.1 to 5.7 mg/dL), total calcium concentration was 9.9 mg/dL (range, 8.1 to 11.7 mg/dL; reference range, 8.2 to 11.8 mg/dL), and ionized calcium concentration was 1.2 mmol/L (range, 0.78 to 1.72 mmol/L; reference range, 1.0 to 1.33 mmol/L). Seven of 52 (13.5%) cats in which a preoperative ionized calcium concentration was available were considered hypercalcemic. The median urine specific gravity was 1.019 (range, 1.006 to 1.050; reference range > 1.035), and urine pH was 6.0 (range, 5 to 7.5; reference range, 6 to 7). Of 35 cats that had urine sediment available for review, 35 (100%) had evidence of hematuria, 30 of 35 (87.5%) had evidence of pyuria, 7 of 35 (20%) had evidence of bacteriuria, 3 of 35 (9%) had evidence of crystalluria (all calcium oxalate), and 1 of 35 (3%) had evidence of renal epithelial cells. Twenty-three of 69 (33%) cats had a UTI prior to stent placement on the basis of urine sediment or bacteriologic culture of urine and antimicrobial susceptibility testing from a cystocentesis or pyelocentesis. Fourteen of the 23 (61%) had culture identification available for review, and they included the following organisms: Escherichia coli (7), Staphylococcus spp (3), Streptococcus spp (2), Klebsiella pneumoniae (1), and Enterobacter aerogenes (1).

Diagnostic imaging—Abdominal radiography was performed and available for review in 68 of 69 cats (98.5%), and ultrasonography was performed and available for review in all 69 cats. Nephroliths were visualized in 67 of 79 (85%) ipsilateral obstructive kidneys, and 50 of 69 (72%) cats had evidence of nephrolithiasis in the contralateral (nonobstructed) kidney. Thirty-five of 79 obstructed kidneys (44%) had evidence of renomegaly, and 15 of 79 (19%) had evidence of a small kidney on the obstructed side. Of the 59 of 69 (86%) unilaterally obstructed cats, 34 (58%) had evidence of a small kidney on the nonobstructed contralateral side. Twenty-six of 69 (37.6%) cats had evidence of bladder stones. The median number of stones in the affected ureter identified on radiographs was 3 (range, 0 to > 50), and on ureteropyelogram, or as identified during surgical manipulation, the median number of stones at the time of stent placement was 4 (range, 0 to > 50). Eleven of 79 (14%) obstructed ureters had no evidence of stones on radiographs or ultrasonography but had stones present at the time of stent placement. Seven of these 11 obstructed ureters where stones were not visualized during routine imaging were obstructed with dried solidified blood stone fragments that were only able to be seen grossly at surgery.

Thoracic radiographs obtained prior to surgery were available for review in 48 cats, and 18 of 48 (37.5%) showed evidence of cardiomegaly, 10 of 48 (20.8%) showed evidence of pleural effusion, and 12 of 48 (25%) showed evidence of enlarged pulmonary vasculature. An echocardiogram was performed in 29 of 69 cats (42%), and abnormalities were documented in 18 of 29 (62%) cases consisting of hypertrophic cardiomyopathy (6/18 [33%]), evidence of fluid overload with left atrial enlargement (5/18 [28%]), left ventricular enlargement (4/18 [22.2%]), left ventricular outflow tract obstruction (2/18 [11%]), pericardial effusion (2/18 [11%]), systolic anterior motion of the mitral valve (1/18 [5.6%]), and unclassified cardiomyopathy (1/18 [5.6%]).

Abdominal ultrasonographic images were available for review in all cats (n = 69). The obstruction was considered unilateral in 59 of 69 (86%) cats and bilateral in 10 of 69 (14%) cats (left sided in 40 and right sided in 39 ureters), totaling 79 obstructed ureters. On the basis of transverse renal ultrasonography, the renal pelvis diameter was a median of 11.5 mm (range, 2 to 29 mm; reference range, < 1 mm). Hydroureter was documented in all ureters proximal to the obstructive lesion, with a median diameter of 3.5 mm (range, 1 to 11 mm; reference range, 0.3 to 0.4 mm). Obstruction location was classified as at the UPJ in 7 of 79 (9%), in the proximal ureter (< 4 cm from the UPJ) in 42 of 79 (53%), in the midureter (4 to 8 cm beyond the UPJ) in 10 of 79 (12.6%), in the distal ureter (> 8 cm from UPJ) in 11 of 79 (14%), or at multiple locations in 9 of 79 (11.4%). One cat had no stones or stricture but had a ureteral obstruction from inspissated purulent material secondary to severe pyelonephritis. The material was palpated throughout the entire ureteral lumen and was causing a ureteral obstruction in multiple locations.

Four of 79 (5%) obstructed kidneys had a preoperative ultrasonography-guided antegrade pyelogram performed. Complications associated with this procedure were evident in 2 of 4 (50%) obstructed kidneys, including extravasation of contrast and subsequent leakage of urine into the peritoneal cavity. An intraoperative antegrade pyelogram was performed in 60 of 79 (76%) ureters prior to stent placement, and a retrograde ureteropyelogram was performed in 19 of 79 (24%).

On the basis of results of a combination of these imaging modalities, as well as surgical exploration, the cause for the ureteral obstruction was considered to be ureterolithasis alone in 56 of 79 (71%) ureters, a ureteral stricture alone in 10 of 79 (13%), a combination of stricture and stone in 12 of 79 (15%), and a purulent ureteral plug in 1 of 79 (1.3%). The diagnosis of a ureteral stricture was based on evidence of a focal ureteral obstruction without a concurrent ureterolith present at the obstructive site, along with a consistent ureteropyelogram showing a blunted narrowing without evidence of an intraluminal filling defect. Without histopathologic findings, this diagnosis was speculative. The diagnosis of a ureteral stricture with concurrent stone disease was more difficult to make and was assumed on the basis of the difficulty in passing the wire through the area, the ureterography imaging showing an obstruction in a separate area from a stone, and evidence of persistent obstruction documented during ureteropyelography after stone removal or manual stone movement from the obstructive location. Histologic examination of the region was available in 3 cats after ureteral reimplantation (n = 2) or on postmortem examination (1). All confirmed the presence of a ureteral stricture.

The presence of a circumcaval ureteral course was detected in 8 ureters, all of which were located in the proximal ureter, and 7 of 8 were associated with suspected ureteral strictures. Not all patients had the proximal ureter dissected for a diagnosis of this condition, and those that had endoscopic stent placement were not evaluated for this. The ureteral obstruction was present within 1 to 3 cm cranial to the area of ureteral and caval crossing in all cases, and 7 of 8 (87.5%) were right sided. One was left sided with a concurrent dual or split caudal vena cava.

Eleven cats had a history of a previous ureteral surgery on the ipsilateral obstructed side, and in 7 of these cats, this was associated with a ureteral stricture at the surgical site as a cause for the ureteral obstruction (previous ureterotomy [n = 5] and ureteral reimplantation [2]), and 4 had recurrence of stones in the ureter. Additionally, 4 strictured ureters had no obvious anatomic malformation or known previous surgery to explain the cause for the stricture. All these lesions were at the UPJ in the very proximal ureter. Dried solidified blood stones were found as the cause of obstruction in 7 of 79 (9%) obstructed ureters, and calcium oxalate stones were suspected as the cause of obstruction in 62 of 79 (79%).

Grading of ureteral obstruction severity—On the scale of 1 through 5, 15 of 79 ureters (19%) were considered a grade 1, 15 of 79 (19%) a grade 2, 18 of 79 (23%) a grade 3, 19 of 79 (24%) a grade 4, and 12 of 79 (15%) a grade 5. In addition, 67 of 79 (85%) obstructed kidneys had ≥ 1 nephrolith. Overall 49 of 79 (62%) of ureters were considered a grade 3 or higher.

Medical management—Intravenous fluid therapy (69 of 69) was used in all patients for a minimum of 24 hours (median, 3 days; range, 1 to 10 days) prior to stent placement attempt. Additional management included α-adrenergic blockade (15 of 69 patients; 21.7%), osmotic diuretic treatment (10/69; 14.5%), nephrostomy tube placement (10/69; 14.5%), intermittent hemodialysis (5/69; 7.2%), and peritoneal dialysis (2/69; 2.8%).

Ureteral stenting procedure—Overall stent placement was successful in 75 of 79 (95%) cat ureters or 66 of 69 (96%) cats. Five ureters required a second procedure to have a successful stent placement, making first-time stent placement successful in 70 of 79 ureters (89%). All these cats were in group 1, prior to the use of the smaller, tapered feline ureteral stent. All cats in which the procedure failed required a temporary nephrostomy tube to be placed prior to a second successful stent placement attempt (n = 5), were converted to the placement of a SUBv device (3), or had a ureteronephrectomy (1) performed. Of 4 stent placement failures, stent placement was attempted prior to the development of the smaller, tapered, and stiffer feline stent in 3 instances, making the success rate in stent placement with use of this stent (group 2) 52 of 53 (98%) versus 22 of 25 (88%) for group 1.

Endoscopic approach—Twenty-one female cats had an endoscopic attempt made for ureteral stent placement, with 4 of 21 (19%) being successful (Figure 2). Eleven of 21 cats had attempts with the older stent model (group 1), and 10 of 21 were in group 2. All 4 successes were in group 1. During cystoscopy in 1 cat there was overdistension of the urinary bladder resulting in bladder hemorrhage and loss of mucosal integrity. One of 4 cats underwent successful endoscopic stenting for a ureteral stricture secondary to a previous ureterotomy, and the other 3 patients were similarly treated for ureterolithiasis. The median procedure time was 85 minutes for endoscopic stent placement (range, 35 to 165 minutes).

Surgical approach—Seventy-one of 75 (95%) cat ureters, in 61 of 65 cats (94%), were successfully stented with surgical assistance. Placement was accomplished through nephrostomy needle access in 38 of 71 (53%); through a ureterotomy incision in 20 of 71 (28%); in a retrograde manner via a cystotomy and catheterization of the UVJ in 8 of 71 (11%); with a combination of a ureterotomy, cystotomy, and nephrostomy access in 4 of 71 (5.6%); and by means of ureteral reimplantation in 1 of 71 (1.4%). Magnification with surgical loupes (n = 32) or a surgical microscope (1) was used when a ureterotomy, reimplantation, or catheterization of the UVJ without endoscopic assistance was performed.

A closed suction drainr was placed in 19 of 61 (31%) cats after stent placement, and a locking-loop nephrostomy tube was placed in 8 of 71 (11%) obstructed kidneys. A urethral catheter was placed in 42 of 61 (69%) cats after their procedure to monitor urine output for a median of 1.8 days (range, 0.17 to 8 days). Procedure time for surgery was a median of 110 minutes (range, 40 to 360 minutes). There was a significant (P = 0.004) difference in the median procedure time for patients in group 1 (155 minutes; range, 35 to 230 minutes) versus those in group 2 (105 minutes; range, 40 to 360 minutes).

Periprocedural data and management—Stones were retrieved for analysis in 26 cases (bladder or ureter), with 20 (77%) being calcium oxalate (18 calcium oxalate monohydrate, 1 calcium oxalate dihydrate, and 1 both monohydrate and dihydrate) and 6 (23%) being dried solidified blood stones. Within the first 48 hours, the median maximum IV fluid rate was 6 mL/kg/h (range, 2.88 to 30 mL/kg/h [2.7 mL/lb/h]). The median amount of fluid accumulated in the closed suction drain within the first 24 hours was 1.5 mL/kg/h (range, 0.16 to 5.4 mL/kg/h). The drain was left indwelling for a median of 1.5 days (range, 0.5 to 14 days). The patient with the drain in place for 14 days had a nephrostomy tube placed at a referral institution that had dislodged prior to evaluation for stent placement, leaving a large defect in the renal parenchyma. A uroabdomen was diagnosed on evaluation of paired creatinine and potassium concentrations in 6 of 69 (8.7%) patients; 1 of the 6 had the uroabdomen prior to surgery for stent placement, making 5 of 69 (7%) associated with the stent placement procedure. Two cats had urine leakage from a ureteral tear during stent placement (spontaneously resolved over 48 hours), 2 had urine leakage from a ureterotomy incision (resolved within 2 and 4 days with a closed suction drain), and 1 had urine leakage from the stay suture site in the urinary bladder requiring a reoperation. An additional cat had suspected urine leakage into the subcutaneous space from a nephrostomy tube catheter though paired samples were unable to be obtained for confirmation.

Twenty-three cats were placed on a mannitol continuous rate infusion after stent placement, and 37 cats had an esophagostomy tube placed for enteral water infusion at a median rate of 2.5 mL/kg/h (range, 0.5 to 4.1 mL/kg/h [1.1 mL/lb/h]). Thirty-two cats were started on 0.45% sodium chloride with 2.5% dextrose (2.5 mL/kg/h [1.1 mL/lb/h], IV) in addition to a balanced electrolyte solution.

Postprocedural data—The median BUN concentration, creatinine concentration, and PCV recorded prior to discharge were 33 mg/dL (range, 14 to 167 mg/dL), 2.1 mg/dL (range, 1.0 to 11.8 mg/dL), and 23% (range, 14% to 37%), respectively. The median renal pelvis diameter based on transverse ultrasonography following stent placement at first recheck examination was 3.5 mm (range, 0.0 to 26 mm). Nine of 39 (23%) cats tested had positive results of bacteriologic culture of urine prior to discharge, consisting of the following organisms: E coli (n = 4), Klebsiella spp (3), coagulasenegative Staphylococcus spp (1), and Enterococcus spp (1). All 9 of these cats had a urethral catheter placed after surgery, although overall, 42 cats had a urethral catheter placed postoperatively (9/42 [21%] having a positive culture result following catheter placement). Those with a positive culture result had a urethral catheter indwelling for a median of 42 hours (range, 12 to 96 hours). Positive results of bacteriologic culture of urine were documented in 31.7% (19/60) of cats short term (≤ 1 month) and in 13% (6/46) of cats long term (> 1 month) over the course of the study. The median hospital stay for cats that survived to discharge was 4 days (range, 1 to 14 days).

Procedural complications—Major procedure-related complications occurred in 7 of 79 (8.9%) obstructed kidneys (6/69 [8.7 %] cats). Six of these complications were associated with a uroabdomen (ureteral tear [n = 2; both in the same cat], ureterotomy leakage [2], nephrostomy tube leakage [1], and bladder stay suture site leakage [1]). One stent was inadvertently placed through the renal pelvis and into the renal parenchyma, requiring stent withdrawal into an appropriate position. Two (2.8%) of these patients needed to return to surgery for fixation of a complication (the bladder leak and stent malposition). All other complications resolved spontaneously without consequence. All but one of these complications occurred in group 1. There were 16 of 75 (21%) minor procedure-related complications that had no clinical effect on the patient: 3 of 75 (4%) ureteral mucosal intussusceptions and 13 of 75 (17%) had ureteral guide wire wall penetrations.

One cat was found to have a renal pelvic rupture at the cranial pole of the kidney. This was found during exploratory surgery, prior to ureteropyelography, and was likely from the increased back pressure due to the ureteral obstruction, rather than procedure related. This patient did not have any postoperative complications after stent placement.

Immediate postoperative complications—The only complications immediately after the procedure (< 1 week) that were considered procedure related were pollakiuria or stranguria in 3 of 66 (4.5%) cats, which in all cases resolved within 7 to 10 days without treatment. The remaining 3 complications were associated with the nephrostomy tubes (subcutaneous leakage of urine around a nephrostomy tube [n = 1], accidental stent dislodgement during nephrostomy tube removal [1], and urine leakage through a previous nephrostomy hole after tube removal [1]). The leakage resolved with tube replacement (n = 2), closed suction drainage (1), and stent repositioning (1).

Eleven of 66 (17%) cats developed signs of congestive heart failure, which was determined on the basis of echocardiographic and thoracic radiographic findings of an enlarged left atrium, dilated pulmonary veins, and evidence of pleural effusion. Three of those cats died. Progressive signs of pancreatitis were present in 4 cats, all of which had evidence of pancreatitis on ultrasonography prior to ureteral stent placement and 2 of which died of pancreatitis-related issues (hematemesis, hypotension, and severe intractable vomiting). Both had a postmortem examination, and the cause of death was suspected as pancreatitis. Interestingly, both cats that died of pancreatitis also had improvements in creatinine concentrations and were not azotemic at the time of euthanasia. Finally, 1 cat had an inverted prepuce and abnormal urethral opening, with a history of stranguria prior to stent placement. After urethral catheter placement, this patient developed recurrent urethral obstructions with no evidence of stone disease. A perineal urethrostomy was ultimately performed 1 week after stent placement, and the straining immediately resolved.

Short-term complications—Short-term complications (1 week to ≤ 1 month) were assessed in the 61 cats stented that survived > 7 days and occurred in 6 of 61 (9.8%) cats. Four cats had evidence of stranguria or pollakiuria, which spontaneously resolved in 2 cats and required intervention in the other 2. One cat had a stiff stent exchanged to a softer one through a small cystotomy, and another cat had a temporary urethral stent placed with a polyurethane catheter, resulting in resolution of the stranguria. One cat had antegrade stent migration into the urinary bladder approximately 3 weeks after surgery. This stent was removed by means of endoscopic retrieval. This patient reobstructed the ureter 9 months later, and a SUB device4,b was placed at that time. One additional cat (1/61; 1.6%) developed progressive renal azotemia. The renal pelvis was decompressed, and no postrenal cause was identified. It was suspected that this was likely due to anesthetic renal insult. Over the following month, the creatinine concentration steadily improved.

Long-term complications—Long-term complications (> 1 month or persistence of short-term complications) occurred in 20 of the surviving 60 cats (68 ureters). These complications included reobstruction of ureters (13/68 [19%]) due to a new retroperitoneal adhesion or stricture around the ureter (3/68 [4.4%]), ureteral stricture recurrence (7/68 [10%]; 4 with concurrent circumcaval ureters and 3 at previous ureterotomy or reimplantation site]), pyelonephritis (1/68 [1.4%]), suspected proliferative ureteral mucosal hyperplasia or ureteritis (2/68 [2.9%]), ureteral stent migration (4/68 [5.9%]; 3 antegrade and 1 retrograde); bladder irritation (2/68 [2.9%]) requiring stent exchange to a softer or shorter stent, and ureteral reflux requiring partial distal stent resection (1/48 [1.4%]). Cats with bladder irritation typically showed signs of dysuria (pollakiuria, periuria, and stranguria).

Stent exchange (short or long term) was required in 19 of 70 (27%) stented ureters after discharge from the hospital. This was necessary because of stent occlusion, migration, or stent irritation, and the stent was replaced with a new ureteral stent (n = 14 ureters) or a SUB device (5). A new stent was placed on an outpatient basis by a keyhole cystotomy with a guide wire exchange to maintain ureteral access. This was typically exchanged for a larger stent (3.7F) or alternative length. A SUB device was typically used when occlusion was due to a ureteral stricture, ureteral mucosal hyperplasia, or severe dysuria. Exchange was performed a median of 67.5 days after original stent placement (range, 10 to 545 days). No patient in this report required a third stent exchange. Passive ureteral dilation was documented in 17 of 19 ureters requiring ureteral stent exchange, allowing for a larger (3.7F or 4.7F) or softer (2.5F) stent to be placed when indicated. Most commonly, stents could be exchanged on an outpatient basis.

The most common minor complication was temporary dysuria (stranguria ± pollakiuria). This was documented in 23 of 61 (37.7%) cats at some point following stent placement but was only persistent in 1 of 60 (1.7%) long term (> 30 days). This resolved spontaneously in 10 of 23 cats and required some combination of the following in 12 cats: anti-inflammatory doses of corticosteroids in 10 cats, prazosin in 2 cats, amitriptyline in 1, a stent exchange in 2 (one shorter and the other softer), and placing a temporary urethral stent (which was then exchanged to a SUB device) in 1. Eight (13%) cats had some degree of pollakiuria. This was defined as > 4 visits to the litter box/day. The pollakiuria resolved in 2 and was persistent in 6 cats. There was no association between the surgical approach (retrograde vs antegrade ureteral stent placement) and dysuria in the short term (P = 0.64) or long term (P = 0.49). Persistent or intermittent hematuria unassociated with a UTI was reported in 11 of 60 (18%) cats at some point after stent placement; none of these cases resulted in progressive anemia or obstructive blood clots.

When variables were evaluated for causes of stranguria or pollakiuria, both short term and long term, there were no significant associations between the patients that had soft and stiff stents (short term, P = 1.0; long term, P = 0.56), patients in group 1 or 2 (P = 0.90), length of the stent (in millimeters) indwelling in the urinary bladder (short term, P = 0.55; long term, P = 0.40), overall stent length chosen (short term, P = 0.08; long term, P = 0.73), history of a UTI prior to (short term, P = 0.35; long term, P = 0.70) or after (short term, P = 0.08; long term, P = 0.66) stent placement, sex (short term, P = 0.20; long term, P = 0.69), or unilateral versus bilateral stenting (short term, P = 0.72; long term, P = 0.56).

Positive results of bacteriologic culture of urine were documented in 19 of 60 (31.7%) cats at some time point after stent placement, and 18 of 19 (94.7%) infections were successfully resolved with appropriate antimicrobial treatment. Nine of 19 (47%) cats with positive cultures were documented to have a UTI at the time of discharge, and all 9 of these cats had a urethral catheter placed after surgery. An Enterococcus sp infection in 1 cat could not be resolved, and this patient was subclinically affected. Six of 46 (13%) cats were documented to develop a UTI at some point long term.

Follow-up—None of the 61 cats that survived to discharge had known evidence of ureteral obstruction recurrence secondary to ureteral stone disease. The main reason for reobstruction was recurrent ureteral strictures documented by obstruction at the site of either a previous surgical location (ureterotomy or reimplantation site) or a previous stricture site as well as the lack of any stones found at this site. Only 1 cat had evidence of recurrent cystolithiasis requiring a voiding urohydropropulsion.

The median creatinine concentration in all patients was 2.4 mg/dL (range, 1.5 to 10 mg/dL) at 3 months after stent placement and 2.6 mg/dL (range, 1.3 to 11 mg/dL) at the time of last follow-up. The most recent renal pelvis diameter on transverse ultrasonographic imaging at the time of last follow-up was 2.4 mm (range, 0 to 20 mm). The patient with the 20-mm pelvic dilation was not obstructed on antegrade pyelography, and a cystogram showed evidence of ureterovesicular reflux. The treatment for this was cutting of the distal end of the stent to prevent it from traversing the UVJ.

Outcome—Sixty-one of 66 (92.4%) cats that had a stent placed survived to discharge. The 5 cats that did not survive were euthanized because of refractory congestive heart failure (n = 3) or pancreatitis (2). No cat died of complications from the stenting procedure, renal failure, or a ureteral obstruction prior to discharge. The overall MST from the time of surgery was 498 days (range, 2 to 1,262 days), with 32 of 66 (48.5%) cats still alive at the time of last follow-up. Only 14 of 66 (21%) cats ultimately died of suspected or confirmed progression of chronic kidney disease. The MST of the 14 cats that died of chronic renal failure was > 1,262 days (median not met), and the mean was 450 days. For cats with a renal cause of death (n = 14), the survival rate at 1 month, 6 months, 1 year, and 2 years was 98%, 90%, 86%, and 86%, respectively, whereas the overall survival rate for all stented patients (66), regardless of cause of death at 1 month, 6 months, 1 year, and 2 years was 91%, 75%, 65%, and 37%, respectively. No cat was known to die of recurrent ureteral obstruction long term. The remaining cats died of causes unrelated to their chronic renal or ureteral disease, and only 2 of 66 cats had a cause of death that was unknown. The cause of death in the 34 cats reported was considered renal or likely renal in 14, unlikely renal or ureteral in 5, definitely not renal or ureteral in 13, and unknown in 2. Deaths that were unlikely to be from renal-associated disease were congestive heart failure (n = 6), pancreatitis (3), seizures or neurologic signs (2), neoplasia (2), renal transplantation complication (1), a femoral fracture (1), owner compliance and convenience (1), gastric perforation from parasites (1), and chronic progressive gastrointestinal disease (1). The only significant (P < 0.001) predictor of survival was the IRIS stage at 3 months after stent placement. At 3 months, for every 1 unit increase in creatinine concentration (mg/dL) the hazard ratio increased by 1.26. When survival time was broken down by IRIS stage 1 through 4 at 3 months after stent placement, the MSTs were 1,262, 1,262, 395, and 94 days, respectively (Figure 4).

Figure 4—
Figure 4—

Kaplan-Meier survival curves documenting patient survival in 69 cats undergoing ureteral stenting for benign ureteral obstruction from 2006 to 2010. A—Overall survival time of all cats with an MST of 498 days (range, 2 to 1,262 days). B—Median survival time of cats based on IRIS stage at 3 months after surgery (stage 1 [S1] = creatinine concentration < 2.0 mg/dL; stage 2 [S2] = creatinine concentration 2.0 to 2.8 mg/dL; stage 3 [S3] = creatinine concentration 2.9 to 5.0 mg/dL; and stage 4 [S4] = creatinine concentration > 5.0 mg/dL). Median survival time of cats classified by IRIS stage was as follows: stage 1, > 1,262 days (mean, 507 days; range, 295 to 1,278 days); stage 2, 1,262 days (mean, 990 days; range, 148 to 1,262 days); stage 3, 395 days (mean, 433 days; range, 90 to 1,200 days); stage 4, 94 days (mean, 203 days; range 90 to 500 days). There was a significant (P = 0.008) difference between survival time for IRIS stage 1 and stage 4 patients (P = 0.008) as well as IRIS stage 2 and stage 4 (P = 0.002). For IRIS stage 2 versus stage 3, survival time was not significantly different (P = 0.06). C—Kaplan-Meier survival curve for cats undergoing urethral stenting for benign ureteral obstruction, with patients that died of causes unrelated to renal or urinary tract disease censored from the analysis. Median survival time was > 1,262 days (range, 2 to 1,262 days).

Citation: Journal of the American Veterinary Medical Association 244, 5; 10.2460/javma.244.5.559

Statistical analysis—The following risk factors were evaluated for their association with survival but were not found to be significant: prestenting hemodialysis, unilateral or bilateral ureteral obstructions, preoperative creatinine concentration, or length of hospitalization on short- or long-term survival. The only significant (P < 0.001) association with survival was the 3-month poststenting creatinine concentration.

Preoperative biochemical parameters were evaluated for their association with survival. Phosphorus had a significant (P = 0.013) influence on survival. For every 1-unit increase in phosphorus, the risk of dying increased by a factor of 1.14 (95% confidence interval, 1.03 to 1.26 [the hazard rate increased by 14%]). Twenty-five of 51 (49%) cats where data were available were hyperphosphatemic.

For biochemical values evaluated at the time of patient discharge from the hospital, an elevated creatinine concentration (hazard ratio, 1.26; 95% confidence interval, 1.12 to 1.42; P < 0.001) and BUN concentration (hazard ratio, 1.01; 95% confidence interval, 1.00 to 1.02; P = 0.003) had a negative association with survival time, with 63 of 66 (95%) cats having an elevated creatinine concentration and 56 of 66 (85%) an elevated BUN concentration. Also, a lower PCV at the time of discharge had a negative association with survival rate (hazard ratio, 0.90; 95% confidence interval, 0.84 to 0.96; P = 0.002).

On the basis of separate univariate Cox proportional hazards regression models, the following preoperative biochemical parameters had no association with survival rate: PCV, total protein concentration, potassium concentration, sodium concentration, magnesium concentration, total calcium concentration, ionized calcium concentration, urine protein-to-creatinine concentration ratio, and urine specific gravity. The following biochemical parameters prior to discharge that had no association with survival rate: sodium concentration, potassium concentration, phosphorus concentration, magnesium concentration, total calcium concentration, ionized calcium concentration, urine protein-to-creatinine concentration ratio, and urine specific gravity.

Risk factors for the need for a stent exchange were evaluated, including an underlying ureteral stricture, the need for a ureterotomy, the presence of a UTI before or after ureteral stent placement, the location of the ureteral obstruction in the ureter, and the side of the ureteral obstruction. The only significant risk factors associated with stent exchange (no vs yes) were the presence of a UTI after ureteral stent placement (18.0% vs 57.9%; P = 0.002) and the presence of the obstruction in the proximal third of the ureter (46.9% vs 85.0%; P = 0.004). Of the 13 cats that had a stent reobstruction, 4 had a ureterotomy performed either prior to or during stent placement, and 4 had a circumcaval ureter present associated with a ureteral stricture; therefore, 8 of 13 reobstructions were due to a ureteral stricture, but this association was not significant (P = 0.28).

Of the risk factors that were evaluated for stranguria or pollakiuria (stent length, amount of excessive stent inside the urinary bladder, the presence of a UTI before or after stent placement, sex, stent type [soft, stiff, group 1, or group 2], and the presence of a bilateral or unilateral stent), none were found to be significant.

Discussion

Results of the present study of 69 cats indicated that ureteral stenting is an effective treatment for benign feline ureteral obstruction regardless of stone number, obstructive location, or etiology of the obstruction. Short- and long-term complications were typically minor but may necessitate stent exchange, particularly when associated with ureteral strictures. Stent exchange was needed in 27% (19/70) of ureters and was most commonly needed because of reobstruction (19%), stent migration (5.9%), or stent irritation (2.9%). Dysuria (23/61 cases; 37.7%) at any point in the study was the most common minor complication, but was only persistent in a small number of cases (1/60; 1.7%) long-term.

In this study, ureteral stents were successfully placed in 96% (66/69) of cats (95% [75/79] of obstructed ureters) for various causes (ureteroliths [71%], a ureteral stricture [13%], both ureteroliths and ureteral stricture [15%], or a mucopurulent plug [1%]). Regardless of etiology or anatomic location, a similar approach was taken in the management of each case and no association was found between long-term outcome and cause. All patients had an initial attempt at medical resolution of the obstruction prior to the consideration of interventional or surgical management. In previous studies,1,2 medical management was effective in stone passage or movement in only 8% to 13% of cases. All patients in the present study had not responded to medical management for at least 24 hours prior to the placement of a double-pigtail ureteral stent. In this study, 62% of cats were considered poor surgical candidates (grade 3 or higher), by use of our grading system, on the basis of the number of stones (median, 4; range, 0 to > 50), the proximal location of the ureteral obstruction, and the presence of a ureteral stricture (28% overall and 13% witout concurrent ureteroliths). Additionally, a majority of patients (85%) in this study had concurrent ipsilateral nephroliths present at the time of the ureteral obstruction diagnosis. This makes it difficult to compare this population with those in other studies, in which patients were all considered surgical candidates for stone disease.2

In a previous study by Kyles et al,2 the greatest risks for poor outcome were preoperative hemodialysis, the use of a nephrostomy tube, and the presence of concurrent ipsilateral nephrolithiasis. In this study, there was no negative impact on survival for any of those parameters, with 10% of patients receiving preoperative dialysis treatment (and all surviving > 1 year), 22.7% of patients having a nephrostomy tube placed (either preoperatively or intraoperatively), 85% having ipsilateral nephrolithiasis, and no patient reobstructing from another stone. In this study, 23% of cats had a previous ureteral surgery for stone disease and reobstructed the ipsilateral ureter. In the previous study,2 40% of cats reobstructed within 2 years after surgery, and 86% of these had evidence of nephrolithiasis on initial imaging. This suggests that the presence of nephroliths could be a risk factor for reobstruction with traditional ureteral surgery, making 85% of patients described in this report at high risk for reobstruction from that factor alone, though no patient in this study reobstructed their ureter because of stone recurrence after stent placement.

Ninety-five percent (66/69) of patients were azotemic at initial evaluation (median, 5.3 mg/dL). At the 3-month poststent recheck examination, the median creatinine concentration improved to 2.4 mg/dL, placing most cats in IRIS stage 2. Of all parameters evaluated, the 3-month poststent creatinine concentration was the most significant predictor of long-term survival time, supporting a recent report5 on predictors of outcome after treatment of ureteral obstructions in cats. Patients in IRIS stage 2 at 3 months after stent placement had an MST > 1,262 days, compared with those with higher IRIS stages (stage 3 [395 days] and stage 4 [93 days]), when all causes of death were included. The overall MST for all patients was 498 days, although only 21% died of chronic kidney disease. When survival rate was determined on the basis of ureteral or renal cause of death, MST was > 1,262 days, and the 1-month, 6-month, 1-year, and 2-year survival rate was 98%, 90%, 86%, and 86%, respectively, suggesting that, with appropriate and aggressive treatment, cats with a ureteral obstruction can have a good prognosis regardless of creatinine concentration on initial examination, and should be considered candidates for ureteral decompression for the best chance of a good long-term outcome.

The presence of a ureteral stricture was seen in 22 of 79 (28%) ureters. This was a larger percentage than expected. The strictures were most commonly associated with either a previous ureteral surgery or the presence of a circumcaval ureter. In this and other studies,8,c strictures from a circumcaval ureter are typically found in the proximal right ureter (85%) within 1 to 3 cm from the UPJ. They have rarely been reported in the veterinary literature8,32,33,c and, when found, can be either an incidental finding or associated with a ureteral obstruction. They were recently documented in 17% of ureterally obstructed cats.c Ureteral strictures have been seen in humans with concurrent circumcaval or retrocaval ureters.34–36 The ventrally displaced caudal vena cava can cause external compression of the ureter during development, resulting in a narrowing of the ureteral lumen that has been shown to result in focal ureteral sclerosis and muscular hypertrophy.34 This developmental anomaly is a result of the posterior cardinal vein persisting as the renal segment of the caudal vena cava. Because the posterior cardinal vein is located ventral to the ureter, the ureter becomes entrapped.34 The stricture may not be in the exact location as the crossing cava at diagnosis because the ureteral tube migrates during further development. In humans, this condition is reported to predominantly affect the right ureter and manifests later in life. In this study, 7 of 8 were right sided (85%).

In our clinical experience, patients with ureteral strictures were found to be more difficult to stent, likely owing to the proximal location of the obstruction, the length of normal nonobstructed ureter distally, and narrowed ureteral lumen. Because of this, most of the ureters had a normal diameter caudal to the obstructed region and passage of the dilator and stent through this normal lumen was more challenging. Another interesting finding was that the need for stent exchange due to reobstruction was seen in 19% of obstructed ureters, but those patients with a ureteral stricture (associated with a circumcaval ureter, a history of previous ureteral surgery, or an unknown cause) were more likely to reobstruct (37%) than were patients without a ureteral stricture (9.8%). This difference was not statistically significant, but we suspect that this is likely associated with the small number of cases evaluated and consider this a clinically relevant finding. It is documented that a ureteral stent causes passive ureteral dilation over the course of days to weeks, and thus the ureteral diameter reaches 4 to 8 times its natural diameter.27,37 This allows for less resistance to urine flow down the ureter and maintains patency of the ureter when there is stent lumen occlusion. With the presence of a ureteral stricture, the fibrous tissue does not allow for this passive dilation. If the stent gets occluded with debris, which would ultimately be expected inside the lumen of most stents over the long term, reobstruction would occur in the area of the stricture where passive dilation does not occur. This reobstruction does not seem to occur with stone disease alone even when the stent lumen gets occluded, allowing for urine drainage around the stent. A recent studyc evaluating 164 feline ureteral obstructions treated interventionally found a reocclusion rate of 0% when a ureteral stricture was treated with a SUB device, compared with 58% when the ureteral stricture was treated with a stent. We currently do not recommend ureteral stenting for cats with suspected ureteral strictures or evidence of circumcaval ureters and are instead placing the SUB device in these patients.8,b,c

Evidence of a UTI was found in 33% of cats prior to stent placement. This did not result in any long-term complications. Following stent placement, 31.7% of cats had a positive bacteriologic culture of urine (≤ 1 month after stent placement), but over the long term (> 1 month after stent placement), only 13% had a positive urine culture. This is likely because of the externalized catheters placed after surgery (urethral catheter or nephrostomy tube). Once these catheters were removed and patients were treated with an appropriate antimicrobial, these infections were typically cleared. This would suggest that a cat at risk for developing a UTI, regardless of the presence of a ureteral stent, may develop another UTI in the future. An externalized catheter after surgery may increase this risk over the short term, but not likely over the long term. In a recent study30 looking at canine and feline patients with externalized nephrostomy tubes, 30% had positive results of bacteriologic culture of urine within the first 2 weeks after tube placement, although many of these patients also had a urethral catheter concurrently. These infections were typically able to be resolved in the long-term. This is consistent with the patients described in the present report, suggesting indwelling ureteral stents are not necessarily the cause of the infection and that an infection is more commonly diagnosed before stent placement and is able to be cleared in the long term with appropriate antibiotic therapy. Avoiding externalized catheters is ideal for the short term, but likely of little consequence in the long term. The large number of patients with a UTI prior to stent placement may be associated with a predisposition to infection associated with the ureteral obstructions and poor urinary defenses (ie, stone disease, low urine specific gravity, and the presence of an implant). One interesting finding was that one of the few significant risk factors our analyses identified was that the need for stent exchange was more likely associated with the presence of a UTI after ureteral stent placement (P = 0.002). This finding needs to be further investigated and may support the suggestion to avoid externalized catheters and completely resolve a UTI prior to stent placement.

In the present study, all patients underwent similar diagnostic imaging procedures to diagnose a ureteral obstruction, and the combination of abdominal ultrasonography and radiography was typically recommended. Because of the high success of ureteral stent placement (96%) for treatment of various causes of ureteral obstructions in cats (ie, partial or complete obstructions, stones, strictures, and concurrent nephroliths and for various anatomic locations), the results of this study suggested that performing preoperative intravenous pyelography, percutaneous antegrade pyelography or CT pyelography prior to treatment of a ureteral obstruction is not necessary. All patients in this study had a ureteropyelogram performed during the stenting procedure to confirm the obstruction and assist in guide wire passage, but this was not needed for the diagnosis preoperatively. The ultrasonographic findings of hydronephrosis and associated hydroureter, to an obstructive lesion within the ureteral lumen, in association with abdominal radiographs documenting stone disease, when present, were diagnostic in all cases for a partial or complete ureteral obstruction and indicated therapy. Additionally, giving a nephrotoxic contrast agent IV to a renally compromised patient (ie, IVP with or without CT) or percutaneously performing an antegrade pyelogram, in which renal puncture and urine leakage can occur, while lengthening the anesthesia time for these preoperative diagnostic procedures is possibly unnecessary.

Studies12–16,38 have shown that, following a ureteral obstruction, the more permanent damage occurs the longer the ureter remains obstructed. These data suggest that prompt and aggressive intervention is necessary when a ureteral obstruction is diagnosed, and treating partial obstructions quickly should be considered. This is extremely important in feline patients, which have been reported39–41 to have a > 30% predilection to develop chronic kidney disease in their lifetime. A majority of cats in this study had a unilateral obstruction (86%) and were concurrently azotemic (95%); these findings are evidence of preexisting renal insufficiency, necessitating immediate decompression to improve the overall renal function and ultimate outcome. Interestingly, this study found no statistically significant association between the known duration of a ureteral obstruction and the overall survival time following stent placement, suggesting that a chronically partial ureteral obstruction should not exclude a patient from being considered a candidate for decompression and treatment at the time of diagnosis.

In the present study we devised a grading system based on ultrasonographic, radiographic, ureteropyelographic, and intraoperative findings in an effort to compare ureteral stenting treatment with that of traditional surgical options. This grading system has not been previously validated and was used for the first time in this study. By following this grading scheme, 38% of patients would have been considered fair surgical candidates (needing ≤ 2 ureterotomies or a ureteral reimplantation, with 85% having remaining nephroliths after surgery), and 62% would have been considered poor or excessively difficult surgical candidates (requiring ≥ 3 ureterotomies, a side-to-end ureteral resection and anastomosis, or a pyelovesicular anastomosis). Regardless of grade, the success of ureteral stent placement, surgery time, and short- and long-term outcome was not significantly different, making all cats with a ureteral obstruction candidates for ureteral stent placement, with a lower perioperative mortality rate that that previously reported for traditional ureteral surgery.

Overall, stent placement was successful in 95% of feline ureters and 96% of cats (19% when stents were placed with cystoscopic assistance and 95% when placed with surgical assistance). There was no significant association with the surgical grading scale, patient weight, stone number, stone size, obstruction location, cause of obstruction, or ureteral length in the success of stent placement or overall outcome. We feel that stent placement is more technically challenging when a proximal obstruction is present because of the small diameter of the unobstructed distal ureter (0.3 to 0.4 mm).

Patients were divided into 2 groups, with group 1 being the earlier group (29%) in which a larger 3F stent was typically used prior to the development of the smaller, tapered, hydrophilic, feline ureteral stent, which is 2.5F (group 2). Most failures and complications occurred in patients in group 1. This may be due to the larger stent diameter, the lack of a ureteral dilation catheter, or the learning curve associated with this procedure. Additionally, the 4 cats (5 ureters) that required 2 attempts at stent placement were all in group 1. Interestingly, 1 cat in group 1 had a very proximal stone obstruction at the UPJ. The stone was removed via a ureterotomy, and the surgical site was strictured 3 days later. At that time a ureteral stent was attempted to be placed. This was unsuccessful in both an antegrade and a retrograde direction, and a nephrostomy tube was placed. Additionally, a guide wire was left indwelling within the entire ureteral lumen for 3 days, extending from the body wall, through the kidney, into the renal pelvis and within the ureteral lumen, entering the urinary bladder. This was meant to promote passive ureteral dilation and improve the chances of stent placement. The presence of this wire for 72 hours was sufficient for passive ureteral dilation to occur, making stent placement possible, as previously described in humans.35 This phenomenon was observed in 17 of 19 cat ureters that required ureteral stent exchange where the ureter was examined. We believe that this is the reason stent exchange is typically a fast, outpatient procedure performed via a simple guide wire exchange, usually accommodating a larger-diameter stent than that initially placed.

Procedure times were significantly (P = 0.004) shorter for patients in group 2 (median, 105 minutes; range, 40 to 360 minutes) versus for patients in group 1 (155 minutes; range, 35 to 230 minutes). This is likely due to a combination of factors: group 1 cats (n = 23) were typically treated with the larger-diameter (3F) stent, which was not designed for cats; no ureteral dilator was available; and we were initially relatively inexperienced with the procedure. The ureteral stent that was designed for the feline ureter (group 2) has a ureteral dilation catheter, is smaller in diameter (2.5F), has a tapered end, and has a hydrophilic coating. The combination of experience and better equipment likely made the procedure technically easier and therefore faster for group 2.

There were few major procedure-related complications associated with ureteral stent placement. The most common minor complication was ureteral penetration by the guide wire (17%), which was not considered of clinical consequence in most cats provided that successful stent placement was achieved. A uroabdomen was documented in 7.2% (5/69) of cats after a ureteral stent was placed. With the use of a closed suction drain, this was typically self-limiting. Since the advent of the feline-specific stent, this has been less common, likely because the smaller tapered stent makes the need for concurrent ureterotomy rare. The immediate postoperative (< 1 week) complications associated with the ureteral stenting procedure were pollakiuria and stranguria, which occurred in 4.5% of cats and resolved without treatment. The most common non–procedure-related complication was the development of congestive heart failure in 11 of 66 cats (17%). A minority had evidence of heart disease prior to stent placement. Despite aggressive treatment, 27% of these cats (4% of all patients) died in the hospital from intractable congestive heart failure. Because of this finding, we currently recommend use of enteral feeding tubes for fluid therapy whenever possible to help reduce the sodium and intravenous fluid load. In addition to enteral fluid therapy (60 mL/kg/d [27 mL/lb/d] of water or unflavored electrolyte solution), half-strength saline (0.45% NaCl) solution with 2.5% dextrose is usually administered at a maintenance rate (60 mL/kg/d) IV, to maintain hydration. If additional fluid therapy is needed on the basis of urine output and hydration status, then a replacement fluid is recommended, with care taken to avoid overhydration by careful monitoring of body weight, central venous pressures, and urine output. Since the start of this conservative fluid protocol, no patient has died of congestive heart failure after resolution of a ureteral obstruction. It is important to monitor electrolytes carefully in patients treated with this fluid plan because hyponatremia can occur and urine output can be high.

Dysuria (pollakiuria or stranguria) was the most common complication seen at any point after ureteral stent placement (23/61 [38%]) in the present study. It occurred in 4 cats within the first month and an additional 19 cats > 1 month after stent placement. This was typically temporary, resolving spontaneously or with medical management (steroid administration or α-adrenergic blockade). Signs were persistent in only 1 cat in this study despite aggressive intervention. Dysuria is also a common clinical problem seen in human patients after ureteral stent placement (4% to 80%).42,43 This is typically thought to be due to the irritation caused by the distal pigtail of the stent on the trigonal region and proximal urethra, the biofilm that develops on the stent, the material the stent is made from, and the extra length of the stent that remains inside the urinary bladder.43 In this study, between groups 1 and 2, 4 types of stent materials and various stent lengths were used, and there was no association found with dysuria in these patients. One patient with bilateral ureteral stents had a temporary urethral stent placed, with the presumption that bilateral stents were causing a partial urethral obstruction, resulting in severe dysuria. This did result in improvement in the dysuria. Because the feline UVJ is positioned in the proximal urethra, the presence of the stent in this region could be irritating and act as a partial urethral obstruction. Interestingly, in > 150 canine patients stented to date in the authors’ practice (unpublished data), < 2.5% developed any signs of dysuria after stent placement. The canine UVJ is within the urinary bladder, rather than the proximal urethra. Additionally, in recent studies5,b,c evaluating the SUB and stent device in large groups of cats as a treatment for ureteral obstructions, dysuria was seen in < 2% of cats after SUB device placement. This device is placed within the urinary bladder at the apex, does not transverse the ureteral lumen, and is made of the same material as the ureteral stent (polyurethane or silicone). This would suggest that the stent location is likely the cause of the dysuria, rather than the stent material. In these studies, cats that had a SUB device placed in exchange for an obstructed ureteral stent, or stent-induced dysuria had immediate resolution of the dysuria.

The need for ureteral stent exchange with a new stent or SUB device was seen in 19 of 70 (27%) ureters in the present study for ureteral reobstruction (and stent occlusion), ureteral stent migration, ureteral reflux, or severe dysuria. This is typically a simple outpatient procedure, but it should be considered with the use of ureteral stents. Interestingly, with use of the SUB device in cats5,b,c reobstruction rates were only 6%, migration rates 0%, and dysuria < 2%. In humans, ureteral stents are usually removed or exchanged within 3 to 6 months.42,43 The reason they are often short-term devices is that a human ureter is large enough for alterative minimally invasive permanent treatments like ureteroscopy, laser lithotripsy, endopyelotomy, or laparoscopic ureteral resection and anastomosis,42,43 and the dysuria and encrustation rates associated with ureteral stents in humans are high.42,43 The feline ureter is only 0.2 to 0.4 mm in diameter17,44; therefore, other definitive minimally invasive options of low morbidity and mortality rates are not typically considered, making traditional surgery, ureteral stent placement, or the SUB device, the main options for cats.

This study had several limitations, most of which pertain to its retrospective nature. However, because the authors’ were involved in all aspects of every case, the treatment algorithms, postoperative care, procedural decisions, and follow-up recommendations were all consistent. Because of the inclusion of patients in group 1, stents that are no longer used or recommended for cats were included. The complications and procedural times were more excessive than might be expected in this group, and these were mostly cases performed during the learning curve process. Since the advent of newer stents and improvement in operator experience, the technical success has improved. The exact cause of death is always difficult to determine in a retrospective study, when postmortem examination is not always performed or available. The cause of death was divided into 6 categories: ureteral, definitely renal, likely renal, unlikely renal, definitely not renal, and unknown. This allowed us to give owners a better sense of long-term survival rate and expectations in cats with ureteral obstructions and chronic kidney disease, which most commonly occurs concurrently. It should also be made clear that because this manuscript was composed by, and data were collected by, the operators who performed each procedure, the details of each case are likely more specific than what one would expect of a traditional retrospective study. This could result in reporting more minor complications than what would have been ascertained from a simple medical record review in other retrospective reports.

Benign ureteral obstructions in cats are most commonly associated with ureterolithiasis alone, ureteral strictures alone, or a combination of both. Results of the present study indicated that regardless of etiology, placement of indwelling double-pigtail ureteral stents has a high success rate (95%) and can be considered in patients that were previously classified as difficult or poor surgical candidates. Regardless of location or cause of a ureteral obstruction, the placement of a ureteral stent can be considered a viable option in most feline patients and has improved perioperative mortality rates when compared with traditional surgical options (7.5% vs 21%).2,10 The preliminary data also show fewer long-term complications (uroabdomen, dysuria, ureteral reocclusion, and stent migration) on the SUB device5,b,c than stents or traditional surgery, especially in cases with primary or concurrent ureteral strictures or a circumcaval ureter. This is likely because ingrowth around the stent or lack of passive ureteral dilation in the strictured region of the ureter is common in these patients and not needed with a SUB device. No deaths occurred in association with ureteral stent placement. There were few major short-term complications, and the most common long-term complications were the need for ureteral stent exchange (27%) and the presence of dysuria (38%). Typically, stent exchange was performed on an outpatient basis with minimal morbidity, and the dysuria often resolved with medical management alone. Appropriate training and understanding of the technique should occur for a successful outcome, as this large series of cases was performed by 1 group with extensive experience in this procedure, and a less favorable outcome might be seen in a different clinical setting.

ABBREVIATIONS

IRIS

International Renal Interest Society

MST

Median survival time

SUB

Subcutaneous ureteral bypass

UPJ

Ureteropelvic junction

UTI

Urinary tract infection

UVJ

Ureterovesicular junction

a.

Berent AC, Weisse CW, Bagley DM, et al. Ureteral stenting for benign and malignant disease in dogs and cats (abstr). Vet Surg 2007;36:E1–E29.

b.

Berent AC, Weisse CW, Bagley DM, et al. Use of a subcutaneous ureteral bypass for the treatment of ureteral obstructions in dogs and cats (abstr). J Vet Intern Med 2011;25:1470–1509.

c.

Steinhaus J, Berent A, Weisse C, et al. Circumcaval ureters in cats with and without ureteral obstructions. A comparative study (abstr). J Vet Intern Med 2013;27:604–756.

d.

Pediatric ureteral stent, 3F, nonfenestrated, Cook Medical, Bloomington, Ind.

e.

Pediatric ureteral stent, 3 F, Optimed, Ettlingen, Germany.

f.

Experimental feline ureteral stent, 1.9F, nonfenestrated, Infiniti Medical LLC, Menlo Park, Calif.

g.

Vet Stent-Ureter feline, 2.5F, multifenestrated, Infiniti Medical LLC, Menlo Park, Calif.

h.

5-French Dawson Mueller Locking loop pigtail catheter, Cook Medical, Bloomington, Ill.

i.

Rigid endoscope, 1.9 mm, Storz Karl Storz Endoscopy, Culver City, Calif.

j.

ISO-C, Fluoroscopy, Seimens, Malvern, Pa.

k.

Pulsera, Fluorscopy, Philips Healthcare, Andover, Mass.

l.

Weasel Wire 0.018-inch hydrophilic angle-tipped guide wire, Infiniti Medical LLC, Menlo Park, Calif.

m.

3F open-ended ureteral catheter, Cook Medical, Bloomington, Ill.

n.

0.034-inch tapered ureteral dilation pusher catheter, Infiniti Medical LLC, Menlo Park, Calif.

o.

Omnipaque, Iohexol 240 mg/mL, GE Healthcare, Princeton, NJ.

p.

Polyglactin 910 suture material, 6–0, 8–0, Ethicon, Somerville, NJ.

q.

Monocryl suture material, 5–0, Ethicon, Somerville, NJ.

r.

Jackson Pratt closed suction drain, Cardinal Health, Dublin, Ohio.

s.

Red rubber drainage catheter, 3.5 or 5F, Bard Medical, Covington, Ga.

t.

Esophagostomy tube, 14F, MILA International, Erlanger, Ky.

u.

SAS, version 9.2, SAS Institute Inc, Cary, NC.

v.

Subcutaneous ureteral bypass device, Norfolk Vet, Skokie, Ill.

References

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