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Outcomes of ureteral surgery and ureteral stenting in cats: 117 cases (2006–2014) OBJECTIVE To evaluate and compare outcomes in cats following ureteral surgery or ureteral stent placement.

Chloe Wormser vmd Dana L. Clarke vmd Lillian R. Aronson vmd From the Department of Clinical Studies-Philadelphia, Matthew J. Ryan Veterinary Hospital, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104. Address correspondence to Dr. Wormser (cwormser@ vet.upenn.edu).

DESIGN Retrospective case series. ANIMALS 117 cats. PROCEDURES Data regarding signalment, history, concurrent disease, clinical signs, clinicopathologic tests, surgical procedures, and perioperative complications (including death) were recorded. Follow-up data, including presence of signs of chronic lower urinary tract disease, chronic urinary tract infection, reobstruction, and death, if applicable, were obtained by records review or telephone contact with owners. Variables of interest were compared statistically between cats treated with and without stent placement. Kaplan-Meier analysis and Cox regression were performed to assess differences in survival time between cats with and without ureteral stents. RESULTS Perioperative complications referable to the urinary tract were identified in 6 of 43 (14%) cats that had ≥ 1 ureteral stent placed and 2 of 74 (3%) cats that underwent ureteral surgery without stenting. Perioperative mortality rates were similar between cats with (4/43 [9%]) and without (6/74 [8%]) stents. After surgery, signs of chronic lower urinary tract disease and chronic urinary tract infection were significantly more common among cats with than cats without stents. Nineteen of 87 (22%) cats with follow-up information available had recurrent obstruction; incidence of reobstruction did not differ between cats with and without stents. Median survival time did not differ between the 2 groups. CONCLUSIONS AND CLINICAL RELEVANCE The potential for signs of chronic lower urinary tract disease and chronic infection, particularly among cats that receive ureteral stents, warrants appropriate client counseling. Judicious long-term follow-up for detection of reobstruction is recommended. (J Am Vet Med Assoc 2016;248:518–525)

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reteral surgery in companion animals is indicated for treatment of congenital abnormalities, trauma, and obstructive uropathy secondary to extramural, mural, or intramural lesions.1–4 With the increase in the number of cats in which obstructive ureterolithiasis has been diagnosed in recent years,2,5–8 ureteral surgery in cats has become more commonplace. Several techniques have been described for treatment of pathological ureteral changes in cats, including ureterotomy, neoureterocystostomy, ureteral stenting, and subcutaneous ureteral bypass.2,5,8–15 The procedure performed is dependent on a multitude of factors, including the cause of ureteral disease, location of ureteral abnormalities, presence of concurrent urinary tract illness, and clinician preference.1–4 There is currently a paucity of veterinary literature describing the short- and long-term outcome in 518

cats undergoing surgical procedures for treatment of ureteral lesions. In the few studies5,9 to date, perioperative complication rates ranging from 6 of 47 (13%) to 27 of 88 (31%) and perioperative mortality rates ranging from 18 of 88 (20%) to 10 of 47 (21%) have been reported for cats treated by ureterotomy or neoureterocystostomy. In recent years, the use of ureteral stents has gained favor, partially because of the reported high complication rates and technical difficulty associated with the aforementioned surgical techniques. Proponents of ureteral stenting have suggested that it may accomplish results similar to those achieved with other ureteral interventions, but in a less invasive manner with potentially fewer complications.11,12,15–17 However, studies10–13,15 have identified complications following ureteral stent placement, including chronic urinary tract infection, stent migration, encrustation

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with particulate debris, and persistent signs of lower urinary tract discomfort.Within the last few years, subcutaneous ureteral bypass has been introduced as a palliative treatment modality for cats with ureteral disease,14 although the long-term effectiveness and complications associated with this technique have yet to be well established. Given the scarcity of information currently available regarding the success of ureteral procedures, the objective of the study reported here was to evaluate shortterm and long-term outcomes in cats treated for a variety of ureteral disorders. Specifically, the study was designed to evaluate perioperative complication rates and mortality rates in cats undergoing ureterotomy, neoureterocystostomy, and surgical ureteral stent placement.

Materials and Methods Case selection

Electronic and hard copy medical records of the University of Pennsylvania Matthew J. Ryan Veterinary Hospital were searched to identify cats that underwent ureteral surgery (ureterotomy or neoureterocystostomy) or open ureteral stent placement between January 11, 2006, and July 23, 2014. Cats with a complete medical record and follow-up information available for ≥ 1 month after surgery were included. Surgical procedural, complication, and outcome data for 10 of the cats in the study that underwent ureterotomy procedures and 12 of the cats in the study that underwent ureteral stenting had been included in other studies.9,12 Those studies did not compare the outcomes of different ureteral interventions and had more limited follow-up. Cats were excluded from the present study if cystoscopic stent placement was performed or attempted.

Medical records review

Records were reviewed and information on patient signalment, presence of concurrent disease, preoperative clinical signs, noninvasive (Doppler) blood pressure measurement at the time of hospital admission, and preoperative serum concentrations of creatinine, phosphorous, potassium, and albumin, as well as BUN and PCV were recorded. Additionally, urine specific gravity and results of urine microbial culture and susceptibility testing were documented. Preoperative thoracoabdominal diagnostic imaging results (echocardiography or abdominal ultrasonography) were evaluated. The surgical procedure performed and any perioperative complications (including death) were recorded for all cases. For study purposes, perioperative complications were defined as negative events occurring during hospitalization.

Surgical techniques

The surgical procedure performed was selected on the basis of the cause and location of ureteral disease as well as clinician preference. All cats were positioned in dorsal recumbency, and a ventral midline laparotomy was performed with complete abdominal exploration. Each affected ureter (unilateral in some

cats and bilateral in others) was isolated and the site of the lesion or anomaly was identified. Surgical operating loupes (2X to 3.5X)a or a surgical operating microscopeb (used at 10X magnification) was used to enhance visibility for all ureterotomy and neoureterocystostomy procedures. All procedures were performed by or under the direct supervision of a boardcertified surgeon, with 6 board-certified surgeons involved in cases included in the study. Ureterotomy was performed by use of previously described techniques.9,18 Briefly, each affected ureter was dissected free from surrounding retroperitoneal tissues at the site of obstruction. Silastic tubing was placed around the ureter, 2 to 3 cm proximal and distal to the obstruction, to stabilize the section of interest, occlude urine flow, and prevent stone migration during ureterotomy. Under magnification, an incision was made directly over the obstruction into the ureteral lumen with a No. 11 scalpel blade. After the obstruction was removed, the ureterotomy site was closed in a simple interrupted suture pattern with either 8-0 nylon or polyglactin 910 suture, according to clinician preference. For end-to-side neoureterocystostomy (reimplantation), each affected ureter was transected at the level of the obstruction and the distal segment was resected.The transected end of the remaining portion of the ureter was then sutured to the urinary bladder mucosa near the apex with an intravesicular18,19 or extravesicular20 technique. For the intravesicular technique, a ventral cystotomy was created, and Kelly hemostats were used to penetrate the dorsal wall of the bladder near the apex. The free end of the ureter was grasped and pulled into the bladder lumen.The ureter was spatulated, and periureteral fat was removed. The anastomosis was made with circumferential simple interrupted sutures of 8-0 nylon or polypropylene suture, selected on the basis of clinician preference. For the extravesicular technique, a small stab incision was made in the bladder wall near the apex.The ureter was spatulated and sutured to the bladder mucosa by placing circumferential simple interrupted sutures of 8-0 nylon, with knots external to the lumen. For ureteral stent placement, a ventral cystotomy was performed, and access to the ureterovesicular junction of the affected ureter was obtained by use of an 0.018-inch-diameter angle-tipped hydrophilic guide wire advanced into the distal aspect of the ureter and passed retrograde into the renal pelvis as described elsewhere.16 A ureteral dilation catheter was advanced over the wire and into the ureter.The dilator was then removed, leaving the wire in place, and a double pigtail ureteral stent (2+F, 2.5F, or 3F) was advanced over the guide wire until one end was secured in the renal pelvis and the other end secured in the urinary bladder. The guide wire was removed, and appropriate stent positioning was confirmed with retrograde ureteropyelography under fluoroscopic guidance.The bladder was closed routinely with absorbable monofilament suture material in a simple interrupted pattern.

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Alternatively, ureteral access was obtained via renal access; a 22-gauge over-the-needle catheter was used to puncture the kidney along the greater curvature, and an intrapelvic injection of iodinated contrast medium diluted 50:50 in saline (0.9% NaCl) solution was administered for evaluation of the course of the ureter and location of the obstruction. A 0.018-inch-diameter angled hydrophilic wire was advanced through the ureter in a proximodistal direction to a point where it crossed the ureterovesicular junction and was then grasped with forceps passed through a ventral distal cystotomy. The dilator catheter was advanced retrograde through the ureter or normograde through the kidney to achieve ureteral dilation. The stent was placed retrograde through the bladder or normograde through the kidney, and stent position was confirmed fluoroscopically.The renal access site was closed with monofilament suture applied in a mattress pattern.

Follow-up

Follow-up information was obtained through a combination of medical records review and gathering information from clients by telephone. Information was collected regarding occurrence of signs of lower urinary tract disease (including chronic hematuria, stranguria, dysuria, or a combination of these signs), development of urinary tract infection, and recurrence of ureteral obstruction after surgical treatment. Signs of chronic lower urinary tract disease were defined as those lasting > 1 month or those recurring ≥ 3 times during the follow-up period in cats with negative results for microbial culture of urine. Chronic urinary tract infection was defined as that persisting > 1 month despite appropriate antimicrobial treatment on the basis of microbial culture and susceptibility testing or infection recurring ≥ 3 times during the follow-up period. For cats with a diagnosis of recurrent ureteral obstruction, the duration of time between surgery and reobstruction and type of treatment pursued at the time of reobstruction were noted. For cats that had died, the date and cause of death (if known) were recorded.

Statistical analysis

Statistical analysis was performed with a commercial software package.c Differences in variables of interest (perioperative mortality rate [including spontaneous death or euthanasia during hospitalization] and proportion of cats with lower urinary tract disease signs, chronic urinary tract infection, or ureteral reobstruction during the follow-up period [ie, any time between hospital discharge and last followup]) were compared between cats with and without stents by means of Pearson χ2 analysis. If a cat had >1 recurrence of ureteral obstruction, only the first reobstruction was included in analysis. A Pearson χ2 test was also used to determine differences in the incidence of ureteral reobstruction between cats with nephrolithiasis and those without nephrolithiasis on initial ultrasonographic evaluation. Survival time for all 520

cats was determined by Kaplan-Meier analysis. A Cox regression analysis was performed to determine differences in survival between cats with and without stents. For all tests, values of P < 0.05 were considered significant.

Results During the study period, 117 cats underwent ureteral surgery with or without open ureteral stent placement and met the study inclusion criteria. Most (89/117 [76%]) of these were domestic shorthair cats, and 11 (9%) were domestic longhair cats. Breeds less commonly represented included Siamese (n = 4 [3%]), Himalayan (3 [3%]), Maine Coon cat (3 [3%]), Persian (2 [3%]), and Devon Rex (2 [2%]). Three of 117 (2%) cats were of other breeds. Median age of cats at the time of surgery was 8 years (range, 1 to 17 years), and median body weight was 4.4 kg (9.7 lb; range, 2 to 7.5 kg [4.4 to 16.5 lb]). Fifty-seven of 117 (49%) were females (55 neutered and 2 sexually intact) and 60 (51%) were males (all neutered). The most common clinical signs in the cats at the time of examination at the study hospital included inappetence (45/117 [38%]), lethargy (32 [27%]), signs of lower urinary tract disease (hematuria, stranguria, or dysuria; 27 [23%]), vomiting (17 [15%]), and weight loss (17 [15%]); some cats had multiple signs. Three (2%) cats had a urethral obstruction at the time of evaluation, and 2 (2%) cats were initially admitted to the hospital because of dystocia but had iatrogenic damage to the ureters during surgical treatment. Nine cats (8%) had no clinical signs on initial evaluation at the study facility but were referred because of clinicopathologic or ultrasonographic abnormalities consistent with urinary tract dysfunction. Forty-six of 117 (39%) cats had a history of medically managed urinary tract disease prior to the visit at the study hospital. These included cats with chronic renal insufficiency (diagnosed a median of 187 days [range, 7 to 620 days] prior to referral examination; n = 24 [21%]), urethral obstruction (8 [7%]), lower urinary tract infection (8 [7%]), acute kidney injury (2 [2%]), polycystic kidney disease, renal agenesis, ureteral obstruction secondary to ureterolithiasis (diagnosed 340 days before referral examination), or idiopathic cystitis (1 [0.9%] each). Five (4%) additional cats had previous urinary tract surgery including cystotomy for cystic calculi (n = 2), ureterotomy for ureterolith removal (performed 200 days before this visit; n = 1), ureteronephrectomy for treatment of renal carcinoma (1), and ureteronephrectomy for treatment of pyelonephritis (1). Results of hematologic analysis for variables of interest at the time of hospital admission were summarized (Table 1). Eighty-six of 117 (74%) cats were azotemic (BUN concentration > 32 mg/dL and serum creatinine concentration > 2 mg/dL), 79 (68%) were anemic (PCV < 37%), 39 (33%) were hyperphosphatemic (serum phosphorous concentration > 6.6 mg/ dL), and 23 (20%) were hyperkalemic (serum potas-

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Table 1—Results of hematologic analysis and laboratory reference ranges for variables of interest in 117 cats that underwent ureteral surgery at a veterinary teaching hospital between January 11, 2006, and July 23, 2014. Variable Creatinine (mg/dL) BUN (mg/dL) Phosphorus (mg/dL) Potassium (mmol/L) Albumin (g/dL) PCV (%)

Reference range 1.0–2.0 15–32 3.0–6.6 3.5–4.8 2.4–3.8 37–55

Admission (n = 117) 3.5 (0.7–21.1) 47 (13–310) 5.8 (3.9–23.2) 4.4 (3.3–8.1) 3.1 (2–4.3) 28 (12–52)

Discharge (n = 107) 2.2 (1.2–7.8) 36 (14–108) 5.1 (2.9–11.6) 4.1 (2.9–5.4) 2.3 (1.5–2.9) 24 (15–35)

Data for study cats are reported as median (range). Ten cats were euthanized or died during hospitalization.

sium concentration > 4.8 mmol/L). The median urine specific gravity at the time of hospital admission was 1.012 (range, 1.005 to 1.069); 72 (62%) cats had a urine specific gravity < 1.012. Microbial culture of a urine sample was performed for 95 of 117 (81%) cats at the time of hospital admission. Of those, 30 (32%) had positive microbial growth, with Escherichia coli isolated from most (26/30 [87%]) cats with infections. Other bacteria cultured included Enterococcus (2 cats), Staphylococcus (1 cat), and Actinobacter (1 cat) spp.The median systolic blood pressure (via Doppler) of the cats at hospital admission was 140 mm Hg (range, 90 to 190 mm Hg); 26 of 117 cats (22%) were hypertensive (Doppler reading > 150 mm Hg). Sixty-three of 117 (54%) cats had a cardiac murmur ausculted on physical examination; of those, 42 underwent echocardiographic evaluation while in the hospital. Cardiomyopathy was diagnosed by this method in 14 cats, including hypertrophic cardiomyopathy (n = 11), hypertrophic obstructive cardiomyopathy (2), and restrictive cardiomyopathy (1).The remaining 28 cats that had echocardiography performed were identified as having physiologic flow murmurs. One hundred fifteen of 117 (98%) cats had preoperative abdominal ultrasonography performed to investigate the urinary tract, and abdominal radiography was performed for 63 (54%). Five (4%) cats underwent contrast urography, and 3 (3%) had abdominal CT performed in addition to ultrasonographic evaluation. Ureterolithiasis was a common finding (102 [87%] cats). Focal ureteral strictures were identified at the level of the urinary bladder trigone in 10 (9%) cats. One cat had a diagnosis of bilateral extramural ectopic ureters, and another had bilateral distal ureteral obstruction secondary to neoplastic infiltration. One cat had bilateral distal ureteral obstruction caused by iatrogenic ureteral ligation and transection during elective ovariohysterectomy 10 days before the evaluation. Of the 117 cats, nephroliths, renal mineralization, and chronic renal changes were detected in 38 (32%), 21 (18%), and 85 (73%), respectively, with some cats having multiple conditions.The 2 cats that did not have abdominal ultrasonography performed before surgery had initially been treated

for dystocia, and iatrogenic ureteral transection occurred at the time of ovariohysterectomy. All cats were administered fluids IV prior to surgical intervention, and 3 cats underwent preoperative hemodialysis. The median interval between hospital admission and surgery was 1.2 days (range, 1 to 4 days). Anesthetic protocols varied among patients and were chosen at the discretion of the attending anesthesiologist. All cats received antimicrobials prior to surgery (some in combination), including enrofloxacin (5 mg/kg [2.3 mg/lb], IV, q 24 h; n = 51), ampicillin sodium (22 mg/kg [10 mg/lb], IV, q 8 h; 47), cefazolin sodium (22 mg/kg, IV, q 8 h; 25), clindamycin hydrochloride (10 mg/kg [4.5 mg/lb], IV, q 8 h; 4), imipenemcilastin sodium (5 mg/kg, IV, q 8 h; 4), cefotaxime (40 mg/kg [18.2 mg/lb], IV, q 6 h; 2), ticarcillin-clavulanate potassium (50 mg/kg [22.7 mg/lb], IV, q 6 h; 2), and cefoxitin sodium (30 mg/kg [13.6 mg/lb], IV, q 8 h; 1). Antimicrobial regimens were chosen on the basis of clinician preference or the results of urine microbial culture and susceptibility testing. Sixty-nine of 117 (59%) cats had a single ureterotomy incision performed on the left ureter (32 cats), right ureter (27 cats), or both ureters (10 cats). One cat had multiple ureterotomies of the left ureter, and 2 cats had multiple ureterotomies of the right ureter. In all cases, ureterotomy was performed for removal of ureteral calculi; in 63 cats, no stents were used.Twelve of 117 (10%) cats had unilateral (n = 10) or bilateral (2) neoureterocystostomy performed (11 without stenting). Reimplantation was performed following removal of, or resection for, distally lodged ureteroliths in 6 cats, stricture of the distal aspect of the ureter in 2 cats, iatrogenic ureteral transection during ovariohysterectomy in 3 cats, and neoplastic obstruction in 1 cat. An intravesicular technique was used in 11 of these 12 cats, and an extravesicular technique was used in in the remaining cat. Forty-three of 117 (37%) cats had ureteral stents placed unilaterally (n = 37) or bilaterally (6); this was done in conjunction with ureterotomy (9) or neoureterocystostomy (1) or as sole treatment for ureteral obstruction (33). Concurrent surgical procedures performed at the time of ureteral intervention included cystotomy (n = 76), esophagos-

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tomy and feeding tube placement (17), nephrostomy tube placement (5), perineal urethrostomy (3), gastrointestinal biopsy (2), renal biopsy (1), and cystopexy (1).A closed-suction peritoneal drain was placed in 19 cats as deemed necessary by the primary surgeon. A perioperative packed RBC transfusion was administered to 44 of 117 (38%) cats. The most common complication in the study population was development of uroabdomen after surgery. This was identified in 8 of 117 (7%) cats that underwent ureteral surgery; median time to diagnosis of this condition after surgery was 4 days (range, 2 to 5 days). Four of these 8 cats had undergone ureterotomy (3 with stent placement and 1 without), 3 had had a ureteral stent placed as sole treatment, and 1 had undergone ureteral reimplantation (without stent placement). The diagnosis was made on the basis of peritoneal fluid analysis in all 8 cases; contrast urography was performed to confirm urine leakage in 3 cats. In 6 of 8 cats with uroabdomen identified, urine leakage resolved with conservative treatment involving urinary catheter placement to maintain bladder decompression. In 1 cat, abdominal reexploration was performed, and leakage from the ureterotomy site was confirmed and repaired primarily; no leakage was observed following the revision. The owners of the remaining cat elected euthanasia at the time of uroabdomen diagnosis. In 2 of 43 (5%) cats that had undergone ureteral stent placement, stent migration was diagnosed ≤ 3 days after surgery. In one cat, the cranial coil of the stent migrated from the kidney into the retroperitoneal space through the renal puncture site created at the time of anterograde stent placement, and in the other cat, the cranial coil of the stent migrated from the kidney into the proximal aspect of the ureter. In both cases, surgery was performed to modify stent position. Other perioperative complications identified in the study population included congestive heart failure attributed to volume overload (n = 4), pancreatitis (3), hepatic lipidosis (3), and sepsis (2); all of these complications developed after surgery and resolved with appropriate medical treatment. Ten of 117 (9%) cats did not survive to hospital discharge following surgery, with death occurring a median of 3 days after surgery (range, 2 to 9 days). Of the 10 cats that died during this time, 4 had undergone ureteral stent placement. The perioperative mortality rate of cats treated with ureteral stents (4/43 [9%]) did not differ significantly (P = 0.52) from that of cats treated with ureterotomy or neoureterocystostomy without stenting (6/74 [8%]). Eight cats were euthanized during this period because of progressive renal failure (n = 7) or uroabdomen (1). Death in the remaining 2 cats was attributed to respiratory arrest of unknown etiopathogenesis. Necropsy was performed on 5 of the 7 cats that were euthanized because of progressive renal failure. Severe, chronic, tubulointerstitial nephritis was diagnosed in 4 cats, and tubulointerstitial nephritis with focal infarction was diagnosed in 1; no obstructive ureteroliths or uroabdomen was 522

observed in any of these 5 cats on necropsy examination. The other 5 cats that died during the perioperative period were not necropsied. For the 107 of 117 (91%) cats that survived to discharge, the median duration of hospitalization was 6 days (range, 2 to 19 days), and median BUN and serum creatinine concentrations at the time of hospital discharge were still slightly greater than the respective reference ranges (Table 1). Thirty-seven of 117 (32%) cats were azotemic at the time of discharge. Uroliths from 68 cats were analyzed; most were composed of calcium oxalate (64/68 [94%] samples), with struvite (n = 2 samples), ammonium urate (1), and blood clots (1) less commonly represented. Follow-up was available for 87 of 107 (81%) cats that survived to hospital discharge. The median follow-up time for these cats was 742 days (range, 34 to 2,800 days). Of these 87, 48 (55%) were still alive at last follow-up, and 39 (45%) had died. Of the cats that had died after hospital discharge, 22 (56%) had been treated with ≥ 1 ureteral stent and 17 (44%) had undergone ureteral interventions other than stent placement (ureterotomy or neoureterocystostomy). Death was attributed to progressive chronic renal failure in 25 cats, ureteral reobstruction in 7 cats (4 with, and 3 without, stents placed), and disease processes unrelated to the urinary tract in 5 cats (congestive heart failure [n = 3], diabetic ketoacidosis [1], and gastrointestinal lymphoma [1]). An unknown cause of death was assigned to the remaining 2 cats. Of the 48 cats that were alive at the time of follow-up, 21 (44%) had been treated with a ureteral stent, whereas 27 (56%) had undergone interventions other than stent placement. For all cats included in this study, median survival time of those treated with ureteral stents (1,575 days; range, 5 to 2,800 days) was not significantly (P = 0.82) different from that for cats that did not have stents placed (1,519 days; range, 2 to 2,650 days; Figure 1).

Figure 1—Kaplan-Meier plot of the overall survival times for 117 cats that underwent surgery for obstructive ureterolithiasis between January 11, 2006, and July 23, 2014, and did (n = 43; dotted line) or did not (74; solid line) have ureteral stents placed. Treatment modality had no significant effect on survival time.

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Seventeen of 87 (20%) cats for which follow-up was available had signs of chronic lower urinary tract disease (hematuria, stranguria, or dysuria) without evidence of urinary tract infection during the follow-up period. Of these cats, 12 had undergone ureteral stent placement as primary treatment, 4 had undergone ureterotomy with concurrent ureteral stenting, and 1 had undergone ureterotomy (with a single incision) without stent placement. The proportion of cats with lower urinary tract signs during the follow-up period was significantly (P = 0.002) higher among those that received a ureteral stent (16/43 [37%]) than those that did not (1/44 [2%]). Ten of the 17 affected cats were successfully managed with intermittent use of analgesic, anti-inflammatory, and antispasmodic medications. The remaining 7 cats required stent modification (3), stent replacement (3), or stent removal (1) to ameliorate signs of urinary tract discomfort. Ten of the 87 (11%) cats had documented chronic lower urinary tract infections during the follow-up period, and 2 (2%) had chronic pyelonephritis. Of cats confirmed to have chronic infection, 7 had a ureteral stent placed, 4 had ureterotomy with concurrent ureteral stenting, and 1 had bilateral ureterotomies performed without concurrent stenting as initial treatment at the study facility. The proportion of cats treated that developed chronic urinary tract infection was significantly (P = 0.004) greater among those that had ureteral stent placement (11/43 [26%]) than among those that did not (1/44 [2%]). Of the cats that had ureteral stents placed, stent encrustation (ie, particulate debris encasing the stent) was identified in 2. Nineteen of 87 (22%) cats had ≥ 1 recurrent ureteral obstruction during the follow-up period.The median interval between initial surgery at the study facility and diagnosis of reobstruction was 203 days (range, 22 to 3,650 days). Of these cats, 10 had ureterotomy performed without stent placement, 7 had a ureteral stent placed, and 2 had ureterotomy with concurrent stent placement as the initial surgical procedure at our facility. There was no significant (P = 0.80) difference in the incidence of reobstruction between cats that received a ureteral stent (9/87, 10%) and those that did not (10/87 [11%]). Reobstruction was diagnosed as secondary to ureterolithiasis in 14 cases, to focal stricture in 3 cases, and to ureteritis in 2 cases. Of the 3 cats that had reobstruction secondary to stricture formation, 2 had ureterotomy performed without stenting and 1 cat had a ureteral stent placed (without ureterotomy). Both cats with obstructive ureteritis during the follow-up period had stents placed (without ureterotomy) as the initial ureteral intervention. Thirty-eight of 117 (32%) cats in the study had nephrolithiasis on initial ultrasonographic examination; however, when incidences of reobstruction in cats with (7/19, 37%) and without (12/19 [63%]) nephrolithiasis on initial examination were compared, no significant (P = 0.10) difference was observed. Reobstruction occurred in the ipsilateral ureter (relative to the ureter affected at the time of initial

treatment at our facility) in 11 cats, the contralateral ureter in 6 cats, and both ureters in 2 cats. At the time of reobstruction, 9 cats were treated surgically; 4 of these had a ureteral stent placed, 2 had ureterotomy without stent placement, and 3 cats had ureterotomy performed with concurrent ureteral stent placement. Five cats were treated conservatively with fluid diuresis at the time of reobstruction, and a successful outcome was achieved in all treated cats. The remaining 5 cats were euthanized at the time of reobstruction diagnosis. A third occurrence of ureteral obstruction was diagnosed for 3 cats, with a median of 120 days (range, 60 to 360 days) after resolution of the second obstructive episode. One of these cats was successfully managed with fluid diuresis; the other 2 cats were euthanized at the time of diagnosis of the third obstruction.

Discussion One of the most pertinent findings of the present study was the high incidence of ureteral reobstruction (19/87 [22%] cats with follow-up information available had ≥ 1 reobstruction event) following intervention, regardless of the technique performed. Additionally, signs of chronic lower urinary tract disease unrelated to infection (reported for 17/87 [20%] cats) and chronic lower urinary tract infection (diagnosed in 10/87 [11%] cats) were relatively common during the follow-up period and were significantly more common in cats that underwent ureteral stent placement than in those that did not. Importantly, perioperative deaths of cats that underwent ureteral surgery with or without ureteral stenting were most commonly attributed to progressive renal failure (7/10 cats that died prior to hospital discharge) as opposed to surgical complications. Lastly, survival times were similar between cats treated with ureteral stents (alone or concurrent with other treatments) and cats that underwent other ureteral procedures for obstructive uropathy. This information should be taken into consideration by clinicians prescribing treatment for cats with ureteral disease or anomalies. Recurrent upper urinary tract obstruction in the cat population examined here was most frequently caused by recurrent ureterolithiasis (14/19 cats with ≥ 1 reobstruction); however, ureteral stricture and ureteritis were also identified. We found no significant difference in rates of reobstruction between cats that underwent different ureteral treatment modalities. It also did not appear that nephrolithiasis was a predisposing factor for recurrent obstruction in the study population, given that the incidence of reobstruction after surgery did not differ significantly between cats with and without nephrolithiasis on initial evaluation at our facility. It should be noted that our findings likely underestimate the true incidence of partial or complete ureteral reobstruction, given that 20/107 [19%] cats that survived to hospital discharge were lost to follow-up. Additionally, the incidence of ureteral reobstruction would best be evaluated through serial ultra-

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sonographic evaluations of the urinary tract after surgery, which was not performed on a routine basis for cats in this study. The high incidence of reobstruction in cats of the present study warrants judicious followup after treatment, regardless of the intervention used to manage the obstruction initially. Minimally, abdominal imaging should be recommended for any cat with persistent or recurrent azotemia or in cats with clinical signs suggestive of recurrent obstructive urinary tract disease. Of the 87 cats for which follow-up was available, 17 (20%) had chronic hematuria, stranguria, or dysuria following ureteral surgery without evidence of infection, and an additional 12 (14%) cats had chronic urinary tract infections (10 with lower urinary tract infection and 2 with pyelonephritis) after the intervention. The proportions of cats that developed these complications after ureteral stent placement (16/43 [37%] and 11/43 [26%], respectively) were significantly greater than those of cats that did not have stents placed (1/44 and 1/44 [2% each], respectively). Similar complications have been found in other studies10,11,21,22 in which the outcomes of ureteral stenting were investigated. Stentrelated infections have also been well documented in human medicine, with bacterial colonization of stents playing an essential role in infection pathogenesis.23–26 It has been well established that the incidence of stentrelated urinary tract infection is directly related to the duration of stenting.27,28 Following bacterial colonization of a stent, biofilm formation ensues, which makes clearance of the infection challenging.29,30 The propensity for device-associated urinary tract infection should be carefully considered by clinicians electing to place ureteral stents or ureteral bypass devices. Minimally, clients should be educated about infection risk, potential management challenges, and possible necessity for implant replacement or removal.Additionally, patients that may be at high risk for infection, including those with concurrent disease and immunosuppressed patients, might be poor candidates for urinary tract implant placement. Although most (10/17) cats with signs of chronic lower urinary tract disease other than infection in the present study were managed medically, modification, exchange, or removal of stents was deemed necessary in 7 of 17 cases. In human patients with urologic abnormalities, it is currently recommended that ureteral stents be removed or replaced every 3 to 6 months to minimize the risk for potential complications,31,32 whereas in veterinary patients, ureteral stents are often left in place for longer periods of time.13,15,33–35 It is the authors’ opinion that this likely reflects the fact that stent removal or exchange in companion animals often requires additional surgical intervention, which owners may be hesitant to pursue owing to added expense, the need for general anesthesia, and invasiveness of the procedure. Clearly, additional research is needed to establish the best medical and surgical strategies for prevention of stent-related complications in cats with ureteral disease because no standardized protocols currently exist. 524

The perioperative mortality rate for cats that underwent ureterotomy or neoureterocystostomy procedures without stent placement in this study (6/74 [8%]) was lower than that in previous reports.5 Many factors may account for this difference, including surgeon experience, variation in equipment, and differences in preoperative patient health status among studies. The perioperative mortality rate (4/43 [9%]) for cats of the present study that had ≥ 1 ureteral stent placed was similar to that reported by investigators of other studies.10,11 As mentioned, regardless of the technique used to address ureteral obstruction, most perioperative deaths in cats of our study were attributable to progressive renal failure, and this was supported by histopathologic findings in cats (5/5) that had necropsy performed. Additionally, of the 87 cats for which follow-up was available in this study, 25 (29%) had died of progressive renal failure. Therefore, it is important to educate owners of the potential for irreversible renal damage despite aggressive surgical and medical intervention and to set appropriate expectations regarding prognosis. The results of this study as well as others5,7 suggest that chronic renal disease is common in cats with obstructive ureterolithiasis. In the present study, 72 of 117 (62%) cats had dilute urine at the time of hospital presentation, and 85 of 117 (73%) cats had chronic renal changes on ultrasonographic evaluation. Although the relationship between chronic renal disease and formation of nephroliths or ureteroliths is unclear, cats with chronic renal disease may be more susceptible to obstructive kidney injury and acute renal failure than cats without the chronic disease.7 Future studies evaluating this and other potential risk factors for the development of renal failure following surgical intervention for ureteral disease may help to identify patients that have a poorer overall prognosis, despite aggressive treatment. Limitations of the present study include its retrospective nature and the fact that a substantial number (20/107 [19%]) of cats that survived to hospital discharge were lost to follow-up. In addition, preoperative and postoperative treatments were not standardized among cats, which may have confounded study results. Lastly, the choice in surgical procedure for cats included in this study was primarily determined on the basis of clinician preference, and the degree of experience with ureteral surgery and stent placement varied among clinicians over the study period. This could have affected the complication rates for cats following ureteral surgery and stent placement in the study. A prospective, randomized study comparing the techniques available for addressing ureteral obstruction or anomalies would provide insight into the benefits and drawbacks of each and may help to establish which patients might benefit most from each intervention.

Acknowledgments No third-party funding or support was received in connection with this study or the writing or publication of the manuscript.The authors declare that there were no conflicts of interest.

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Footnotes a. b. c.

Surgi-Spec Telescopes, Designs for Vision, Ronkonkoma, NY. S88 System, Carl Zeiss AG, Jena, Germany. XLSTAT, version 2015.1.01 for Mac,Addinsoft USA, New York, NY.

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8. 9. 10.

11. 12. 13. 14.

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