Abstract
Ureteral obstruction secondary to ureterolithiasis in cats is a challenging situation. Ureteral stenting has recently been introduced to prevent complications that often occurred after ureterotomy or other invasive surgeries. The purpose of this study is to describe the stenting technique and perioperative difficulties, as well as long-term outcome and complications with ureteral stenting in 12 cats with ureteroliths. Fifteen 2.5 Fr soft double pigtail multi-fenestrated ureteral stents were placed in an anterograde fashion under open surgical approaches and with fluoroscopic guidance in 12 cats. Nine cats received a unilateral stent and three received bilateral stents. Ureterotomy or ureteral resection and end-to-end anastomosis were performed in three and four cases, respectively. In six cats, papillotomy was performed to facilitate dilatator and stent placement. All cats recovered well from the surgical procedure, except one cat, which died during the anaesthesia recovery period. Postoperative complications included dysuria (three cases, diagnosed at 15 days, 1 month and 3 months, respectively), urinary tract infection (one case, 1 month after surgery), stent migration requiring stent replacement (one case, 19 months after surgery) and stent obstruction requiring stent removal (three cases with previously end-to-end anastomosis between 2 and 8 months after surgery). Nine cats (75%) were alive at a mean follow-up of 453 ± 194 (123–720) days. The median survival time was >415 days. Stent placement appeared to be a valuable and safe option for treating ureteral obstruction in cats. However, periodic and long-term monitoring of stents is warranted.
Introduction
Although strictures, dried blood-solidified calculi, blood clots and tumours have been frequently reported, ureterolithiases remain the most common cause of ureteral obstruction in cats, and their perceived incidence has been increasing steadily and consistently for the past 15 years.1–5 Recent studies showed that about 98% of ureteral stones in cats are composed of calcium oxalate. 6 Given the morbidity and mortality associated with ureteral obstruction, early and aggressive treatment is required to relieve the obstruction and prevent further deterioration of renal function.7–12 Medical dissolution was not reported for feline ureterolithiases, and medical treatment relieves the obstruction in less than 20% of cases with persistent azotaemia at 1 month in 70% of cases with a 1 year survival rate of 66%.3,6
Many techniques for the surgical removal of ureterolithiasis have been reported in cats, including pyelotomy, ureterotomy and resection anastomosis ureteral reimplantation. 6 The size of ureters in cats, the frequent presence of multiple uretero- and nephrolithiasis, the variable locations in which calculi can lodge, and the clinical and biochemical status of the animals are important limiting factors causing significant morbidity and mortality.2,3,6,13,14 Despite a 1 year survival of 91%, 6 a perioperative mortality of 18–20% is observed.6,15 Complications occur in 30–50% of cases, such as urinary leakage (6–16%), recurrence (40%) and ureteral stricture.2,6,15,16
In human surgery, the use of ureteral stents has helped in significantly reducing complications associated with ureteral surgery.17–20 In veterinary surgery, the use of ureteral stents has gained favour because it is believed that complication rates may be potentially reduced compared with those observed with standard techniques.13,21–25 The purpose of this study is to describe perioperative difficulties, as well as long-term outcome and complications, of ureteral stenting in cats.
Materials and methods
Twelve cats presented with ureteral obstruction requiring immediate relief were included in the study. They were all presented to the veterinary teaching hospital of the National Veterinary School of Alfort between March 2011 and September 2012 with obstructive ureterolithiasis unresponsive to medical treatment (isotonic sodium chloride [NaCl] intravenous [IV] fluid therapy; amitriptyline: 5 mg PO, once a day [Elavil; Gerda]; alfusozin, 0.1 mg/kg PO, twice a day [Xatral; Sanofi-Aventis]; mannitol infusion: bolus at 0.25–0.5 g/kg over 30 min followed by a continuous rate infusion of 1 mg/kg/min for 24 h [Mannitol 20%; Aguettant]).
Preoperative work-up consisted of complete blood count; biochemistry; electrolytes profile; urinalysis, including urine culture; abdominal radiographs; and ultrasonography. All urinalyses were performed on urine collected through cystocentesis.
Surgical techniques
After a midline celiotomy, the affected ureter(s) was (were) located, and the site of the obstruction was identified. The ipsilateral kidney was isolated with moist gauze and the proximal ureter was dissected free from the surrounding tissue in the retroperitoneal space in order to relieve the sinuous run of the proximal ureter. A 22-G needle catheter was introduced by the great curvature of the kidney and directed toward the pelvic cavity. Urine was withdrawn and submitted for culture; then, contrast medium was infused under fluoroscopic guidance to perform an ureteropyelography. A 0.018" guide wire (150 cm; Weasel Wire, Infiniti Medical) was subsequently inserted by its J-tipped extremity into the renal pelvis through the catheter and manipulated down the ureter, bypassing the obstruction, to the bladder, and was then retrieved through a ventral cystotomy. The catheter was removed and a 0.034" ureteral dilator (dilator-pusher; Infiniti Medical) was introduced over the guide wire from the kidney to the bladder. In cases where it was not possible to pass the dilator through the ureterovesical papilla, a small incision of the urothelium of the papilla was performed (papillotomy). The guide wire was then removed, and re-introduced in a retrograde direction through the dilator, from the bladder to the renal pelvis in order to place the J-tipped extremity cranially on the kidney side. The ureteral dilator was removed and a 2.5-Fr soft double pigtail multi-fenestrated ureteral stent (Vet-Stent-Urete; Infiniti Medical) was positioned over the guide wire before being advanced in an antegrade fashion over the guide. The wire was progressively withdrawn at the bladder side (Figure 1) and the stent was subsequently positioned in the renal pelvis under fluoroscopic guidance until a curl was made.
Perioperative view of a 2.5 Fr ureteral stent placement in a cat before cystotomy closure. The proximal pigtail was correctly positioned in the pelvis under fluoroscopic guidance. White asterisk = left kidney; white arrow = left ureter; black arrow = bladder; Cr = cranial; Cd = caudal
The bladder was closed with a single-layer continuous suture pattern using 4-0 glycomer 631 (Biosyn; Covidien) and omentalised. Postoperatively, antibiotic therapy was administered for 1 week.
Follow-up
Clinical, biochemical, urine and imaging examinations were performed every day after surgery until discharge at 15 days, and 1, 3 and 6 months after surgery, and then every 2–6 months.
Recorded data and statistical analysis
Numerical data were expressed as mean ± SD and range. Pre- and postoperative blood parameters and renal pelvic dilation were compared using the Mann–Whitney test (GraphPad Prism5). The confidence interval was set at 95% and the significance level at P <0.05.
Results
Signalment
Among the 12 cats, there were eight domestic shorthairs, two Birmans, one Siamese and one Persian. Nine cats were spayed females and three were castrated males. The mean age was 5.1 ± 3.2 (1.5–12) years. The mean body weight was 2.9 ± 0.7 (1.6–4.1) kg, with six cats weighing <3 kg.
Clinicopathological data
Preoperative work-up values are summarised in Table 1. Ninety-two percent of cats had creatinine values above the reference interval and 66% of cats had a urine specific gravity <1.035.
Blood work variables and renal pelvis size in all cats. Values are expressed as mean ± SD and (range)
BUN = blood urea nitrogen; PCV = packed cell volume; USG = urine specific gravity; N/A = not available
None of the cats had positive urine cultures at presentation (cystocentesis or pyelocentesis) or crystalluria on sediment examination, but three had gross haematuria.
Diagnostic imaging
Abdominal radiographs revealed ureterolithiases in 8/12 cats studied.
On abdominal ultrasound examination, all cats had evidence of ureteral obstruction, including ureteral dilation and renal pelvic dilation (13.9 ± 5.9 [6–25] mm). The right ureter was the site of obstruction in eight cats and the left ureter in seven cats; nine cats had unilateral obstruction and three cats bilateral obstruction. Additional ultrasonographical findings included hyperechoic periureteral tissue around the obstruction (8/15 obstructive ureter), multiple lithiases in the obstructed ureter (10/15 obstructive ureters), nephrolithiases (<1 mm) ipsilateral to the obstructed ureter (9/15), non-obstructive ureterolithiases (3/9 ureters) and nephrolithiases (<1 mm) (3/9) in the contralateral non-obstructed ureter. These findings revealed that 66% of cats had concomitant ipsilateral nephroliths and 33% had concomitant contralateral nephroliths. The mean cranio-caudal kidney length measured in a sagittal plan was 3.95 ± 0.77 (2.3–5.0) cm in the obstructed kidney and 3.61 ± 0.80 (2.4–5.0) cm in the contralateral non-obstructed kidney (reference interval: 3.8–4.4cm). 26 In cases of unilateral obstruction, the contralateral kidney was small in 5/9 cases (length <3.8 cm).
Antegrade ureteropylography confirmed the obstruction and allowed localisation of the obstruction in all cats (see Figure 3).
Medical management
All patients received isotonic NaCl IV fluid therapy before surgery. Additional medical management included amitriptyline (eight cats), alfusozin (eight cats) and mannitol infusion (five cats). Five cats received a combination of amitriptyline, alfusozin and mannitol infusion, and two cats a combination of amitriptyline and alfusozin. Medical management was maintained for a mean of 3.9 ± 1.4 (1–6) days before surgery.
Surgery
Nine cats received a unilateral stent (right ureter: five cases, left ureter: four cases) and three cats received bilateral stents.
Ureterotomy for lithiasis removal was performed in three cases (at the discretion of the surgeon); mineral analysis revealed oxalate ureteroliths in all cases.
Four cats had ureteral resection and end-to-end anastomosis due to difficulties with stent insertion. In two cases, these resections were due to a stricture distal to the obstructive ureterolithiasis, which prevented the stent placement. In the two remaining cats, the resection was performed following a 1-cm-long ureteral tear during ureteral dilator advancement.
In six cats, papillotomy was performed to allow dilator and stent placement. In these cases, incisions were left to heal by second intention over the stent.
Postoperative radiographs confirmed that all stents were correctly positioned (Figure 2). All cats recovered well from the surgical procedure, except one cat, which had resection anastomosis and died during the anaesthesia recovery period.
Lateral (a) and ventrodorsal (b) radiographic views of a bilateral ureteral stent. Left ureterolithiasis (white arrow) and right nephrolithiasis (white asterisk) were left in place
Clinical outcome
In one cat that received a bilateral stent and which was suspected to have a preoperative urine leakage, peritoneal effusion occurred 24 h after surgery. Exploratory laparotomy was performed, and a minor leak at the catheter insertion site in the right kidney was observed and treated by omentalisation. Recovery was uneventful and peritoneal effusion resolved.
No other case of urinary leakage was observed.
Eleven cats survived and were discharged from the hospital, indicating a perioperative mortality rate of 8%. The mean postoperative duration of hospitalisation was 5.6 ± 3.2 (3–14) days.
During follow-up, all cats showed an improvement in azotaemia, but serum creatinine and blood urea nitrogen (BUN) concentration remained slightly above the reference interval (Table 1).
The abdominal ultrasonographical examinations revealed a progressive, but incomplete, decrease in the dilation of the renal pelvis (Table 1) (3.3 ± 0.5 [3–4] mm, 6 months after surgery).
Both serum creatinine and renal pelvis size showed a statistically significant (P <0.05) improvement when the postoperative values were compared with the preoperative values, or when the 6-month values were compared with the preoperative values (Table 1).
One cat was diagnosed with peritoneal effusion 9 months after surgery. The owners declined further investigation and post-mortem examination, and the cat was euthanased (Supplementary material).
Postoperative urinary tract infection occurred in one cat (Enterococcus faecium), 1 month after surgery, and was successfully treated with antibiotic therapy (Supplementary material).
Three cats (with unilateral stent) developed self-limiting signs of stranguria, pollakiuria and mild haematuria, diagnosed 15 days, 1 month and 3 months after surgery, respectively. None of these cats had a positive urine culture. In all cats, dysuria resolved with anti-inflammatory therapy (prednisolone 0.5 mg/kg PO [OroMedrol; Pfizer], every 12 h for 5 days). In one cat, these signs recurred 12 months after surgery and resolved with the same treatment (Supplementary material).
In one cat, major signs of stranguria, pollakiuria and haematuria developed 19 months after surgery. Urine culture was negative. A stent migration was observed and the stent was removed. A new stent was placed as a 3 mm diameter ureterolithiasis was left in place during the first surgery (Supplementary material).
In three cases (all had ureteral resection anastomosis performed and previously observed nephroliths), stent obstruction was suspected based on an increase in renal pelvis size (17.3 ± 4.6 [12–20] mm compared to 3.3 ± 0.6 [3–4] mm at the previous check-up), in serum creatinine concentration (4.7 ± 1.3 [3.5–6.1] mg/dl compared to 2.0 ± 0.3 [1.7–2.3] mg/dl at the previous check-up) and in BUN levels [154.7 ± 96.8 [66–258] mg/dl compared to 91.0 ± 39.1 [53–131] mg/dl at the previous check-up) between 2 and 3 months after surgery in two cases and at 8 months in the last case (Supplementary material). Ultrasound examinations revealed lithiasis outside and inside the stents; ultrasound-guided and fluoroscopically assisted antegrade pyelography confirmed the stent and ureteral obstruction (Figure 3). Stents were surgically removed in these three cases. Recovery was uneventful in two cats, but the third cat died a few hours after surgery. Macroscopic examination of the retrieved stent showed multiple small (<1 mm) calculi inside and around the stent (Figure 4). Mineral analysis revealed oxalate ureteroliths in all cases.
Radiographic (a,b) and ultrasonographical (c) examinations of a cat with stent obstruction. Note the radiographic dilation of the proximal ureter and pelvis and the proximal attenuation of the opacification on the antegrade ureteropyelogram indicating either a stricture or an encrustation (white arrow) (a,b) and the ultrasonographical appearance of ureteral stone covering the outer and inner surface of the stent in a cat presented with ureteral obstruction. R = right
Appearance of two stents after surgical removal owing to obstruction. Note numerous calculi covering the outer surface of the stents (white asterisk) and obstructing the fenestrations (white arrows)
Nine cats (75%) were still alive at the time of writing, with a mean follow-up of 453 ± 194 (123–720) days. The median survival time after discharge was >415 days (Supplementary material).
Among the survivals, 7/10 (70%) stents were still in place. In the six cats with unremoved ureteroliths, ultrasound examination indicated that the stones spontaneously migrated into the ureter along the stent without causing further obstruction in three cases (50%).
Discussion
Feline obstructive ureterolithiasis is a life-threatening condition that requires early and aggressive treatment.3,16,27 All cats in the present study were surgically treated following medical management failure. In this study, the use of ureteral stent placement for treating ureterolithiasis was associated with a postoperative morality rate of 8% and a 1 year mortality rate of 25%. Except in one case, in which urinary leakage was observed from the catheter insertion site on the kidney, no urinary leakage was observed around the ureter, even when ureterotomy, ureteral resection and end-to-end anastomosis or ureterovesical papilla incision were performed. Leakage was reported to be a minor complication of stent placement that could resolve spontaneously within 24 h. 13 In contrast, in previous reports of surgical removal of ureteroliths which did not use ureteral stent, urinary leakage was observed in 6–16% of cases, necessitating a second surgery in 80% of cases. In these reports, the perioperative mortality rate and the 1 year mortality rate was 18–21% and up to 35% (when associated to perioperative death), respectively.6,15
Different approaches for ureteral stent placement have been described.13,16,27 Cystoscopic and percutaneous radiological approaches are challenging procedures of ureteral stent placement, specifically in small cats. In our study, all stents were correctly placed under open surgical approaches with fluoroscopic assistance. The use of fluoroscopy was very useful as it helped with both the insertion of the stent into the ureter and its correct placement, 13 thereby avoiding stent mispositioning. 27
A common surgical problem encountered (40% of cases) was the need to incise the urothelium of the uretero-vesical papilla to allow dilator/stent placement. Papillae were never sutured and were allowed to heal by second intention over the stent. Complications related to these incisions were never encountered. A smaller, number 2 Fr ureteral stent has since become available (Infiniti Medical), and may have helped to prevent papilla incision.
Failure to direct stent placement occurred in 26% of cases owing to either a stricture distal to the obstruction or a ureteral tear during dilator placement. In these cases, ureteral resection and end-to-end anastomosis were performed to ensure stent positioning. As obstructions were located in the proximal third of the ureter, neoureterocystostomy was not conceivable. 27
Postoperative complications included dysuria (three cases), urinary tract infection (one case), stent migration (one case) and stent obstruction (three cases) (Supplementary material). In the veterinary literature, dysuria is reported in up 35% of cases after ureteral stent placement in cats and could be related to either urothelium bladder inflammation, ureteritis, tissue in-growth or ureterovesicular reflux. 13 Smaller stents, in diameter and/or length, could have prevented such a minor problem; however, nearly all of these complications were manageable with medical treatment. 13 Infection was a minor problem, and only one postoperative infection was observed. The low infection rate recorded in this study is in contrast with other reports that documented up to 20% positivity of postoperative culture.13,16
Stent obstruction was observed in three cases. The obstruction could have been due to tissue in-growth or stent encrustation.13,16,27 Stent encrustation is the major complication observed in people with an encrustation rate of more than 50% 6–12 weeks after surgery. 28 Typically, encrustation is described as mineralisation and stone debris covering the stent.13,17,29,30 In the veterinary literature, indwelling ureteral stents are tolerated well in the long-term, 21 and stent encrustation is a very rare condition, which has only been reported in one case. 27 In our study, mineralisations observed inside and outside the three obstructed stents strongly advocated for stent encrustation. Whatever the cause of stent obstruction observed in our study (tissue in-growth or stent encrustation), the important finding was that all cases in our study had undergone resection anastomosis. It is likely that subcutaneous ureteral bypass device placement was indicated in these cases and would have prevented this complication. Unfortunately, the device was not available in our hospital at this time.13,22,23 This finding indicated that ureteral resection is likely a predisposing factor to stent obstruction. An explanation is that resection anastomosis could cause ureteral stricture, which could thus impair the passage of stones leading to stent obstruction. 2 A passive dilation of the ureter after stent placement has been reported. 31 This may facilitate the migration of nephroliths and ureteroliths along the ureter into the bladder, but such dilation could be prevented by stricture.13,27 Migration of ureteroliths along the stent was observed in our series in 50% of cats.
In previous studies, ureteral stents were successfully used alone with no attempt to remove the stone.21,23,24 One possible drawback of performing ureterotomy is that it could be a predisposing factor for ureteral stricture. However, in our study, none of the cats with ureterotomy displayed stent obstruction, suggesting an ureteral stricture. This may raise the question of systematically removing lithiasis during stent placement because (i) ureteroliths did not systematically migrate along the stent, (ii) potential stricture induced ureterotomy did not seem to lead to stent obstruction and (iii) if the stent needs to be removed (as experienced in the case of stent migration in our study) a new stent has to be placed if ureterolithiasis remained. Further studies are needed to point out the benefits and inconveniences of ureterolithiasis removal.
In our study, the size of the renal pelvis significantly decreased after stent placement compared to the preoperative value, but remained slightly dilated (Table 1). This dilation, which remained self-limited, was likely caused by the proximal pigtail of the stent, which prevented the complete resolution of renal pelvis dilation.13,16,27
Stenting resulted in a significant improvement of all of the tested renal biochemical values, but long-term serum creatinine and BUN concentrations remained slightly above the reference interval in all of cases. This observation was associated with a urine specific gravity <1.035 in 66% of cats, and a serum creatinine and BUN concentration above the reference intervals in 92% of cats before medical treatment, indicating an impairment of renal function before and after stenting. These findings were consistent with reports of feline ureterolithiasis in which 66–90% of cats were azotaemic at the time of presentation.3,6,13,16,23,27,32
Conclusions
Ureteral stenting appears to be a valuable and safe option for treating uni- or bilateral feline ureterolithiasis. Compared with standard ureteral surgery, complications and mortality rates associated with stent placement strongly support the use of this technique to relieve ureteral obstruction, even in small cats weighing <2 kg. However, periodic and long-term monitoring to check for complications related to stents (eg, migration, encrustation, obstruction, dysuria, infection, etc) is warranted.
Supplemental Material
Click here for Supplementary Material
Selected blood parameters before and after stent placements, follow-up and complications in all cats.
Footnotes
Acknowledgements
We wish to thank Professor G Niebauer for his valuable comments on the manuscript and Miss Santin for her assistance.
Supplementary material
Selected blood parameters before and after stent placements, follow-up and complications in all cats.
Funding
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Conflict of interest
The authors do not have any potential conflicts of interest to declare.
References
Supplementary Material
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