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Keywords:

  • Interventional radiology;
  • Ureteral obstruction;
  • Ureteral stricture;
  • Ureteral surgery

Abstract

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Therapeutic Intervention
  6. Discussion
  7. Footnotes
  8. References

Background: Feline ureteral obstructions have emerged as a common problem. Ureteral strictures rarely are reported as a cause and the predisposing factors and clinical course of this condition have not been described.

Objectives: Evaluate cases of feline ureteral strictures and characterize historical features, clinical signs, diagnostic imaging, surgical and endoscopic findings, histopathology, treatment modalities, and short- and long-term outcomes.

Animals: Ten cats diagnosed with ureteral strictures based on compatible findings from at least 2 of the following: ultrasonography, ureteropyelography, surgical exploration, or histopathology.

Methods: Retrospective study.

Results: Median age, serum creatinine concentration, and size of the renal pelvis were 12 years, 3.7 mg/dL, and 11.75 mm, respectively. Six of 10 cats had hyperechoic periureteral tissue on ultrasound examination at the stricture site. Four cats had evidence of a circumcaval ureter at surgery. Eight cats had an intervention including ureteral stent placement (n = 6) and traditional surgery (n = 2). Seven of 8 cats had decreases in serum creatinine concentration and renal pelvic parameters preceding discharge and 6 had persistently improved results at their last examination. All patients survived to discharge. Median survival time was >294 days (range, 14 to >858 days) with 6/10 cats still alive.

Conclusions and Clinical Importance: Ureteral strictures may occur in cats secondary to ureteral surgery, inflammation, a circumcaval ureter, impacted ureterolithiasis, or for unknown causes. With appropriate and timely intervention, the prognosis for long-term survival is good. In addition to ureteral reimplantation or ureteronephrectomy, ureteral stenting or SC ureteral bypass may be considered as future therapeutic options.

Abbreviations:
BUN

blood urea nitrogen

IVF

IV fluid therapy

MST

median survival time

SUB

SC ureteral bypass

UVJ

ureterovesicular junction

Feline ureteral obstructions have emerged as an increasingly common problem in clinical practice. Since the 1st identified case in 1990,1 the perceived prevalence of this condition has been increasing. The majority of feline ureteral obstructions are secondary to calcium oxalate ureterolithiasis, although tumors, strictures, iatrogenic ligation, blood clots, and dried solidified bloodstones have been reported.1–4,a Historical, clinicopathologic, and imaging findings in patients with ureterolithiasis have been reported.2 Some treatment options include temporary nephrostomy tube placement, hemodialysis, ureterotomy, ureteral reimplantation, ureteronephrectomy, ureteral stenting, and renal transplantation.1–4,a

Strictures are defined as a circumscribed narrowing or stenosis of a hollow structure, usually consisting of cicatricial contracture.5 The diagnosis of ureteral stricture ideally is made with the histopathologic finding of fibrosis associated with narrowing of the ureteral lumen. Because biopsy specimens are not typically performed on feline ureters unless a partial ureterectomy or ureteronephrectomy is performed, this diagnosis often is clinically made with advanced imaging or during surgery when obstruction is documented without an intraluminal cause.

In humans, approximately 20% of ureteral strictures are considered asymptomatic.6 There is a predisposition for strictures to form at the ureteropelvic junction, the ureterovesicular junction (UVJ), and the site where the iliac vessels cross the ureter. Predisposing conditions for secondary ureteral strictures include previous ureteral surgery or ureteroscopy, passage of stones, radiation treatment, intrinsic or extrinsic neoplasia, retroperitoneal fibrosis, congenital disease, tuberculosis, circumcaval (retrocaval) ureter, and various drugs. An idiopathic condition (primary stricture) also is described in people.7–10

Ureteral strictures in cats rarely have been reported. There is 1 report of a cat with bilateral, congenital strictures,11 and a single case3 reported among a large series associated with ureterolithiasis. The objective of this report is to describe the condition of feline ureteral strictures, including the clinical presentation, diagnostic findings, and treatment outcomes. To the authors' knowledge, this is the 1st case series describing this condition in cats.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Therapeutic Intervention
  6. Discussion
  7. Footnotes
  8. References

Criteria for Selection of Cases

A computerized medical record search of cats with a diagnosis of a ureteral stricture from 2000 to 2009 was performed. The terms stricture and stenosis were considered synonymous. Cases were included when a ureteral stricture resulting in either a complete or partial obstruction was diagnosed based on 2 of the following criteria: ultrasonography, antegrade or retrograde ureteropyelography, surgical exploration, or histopathology. Cases were excluded if the medical record was considered incomplete for the following details: method of diagnosis, confirmation of diagnosis, method of treatment, renal function test results before and after diagnosis and treatment, and outcome. Other causes of exclusion included that a different cause of obstruction was clearly documented, the stricture occurred at the site of a previous surgical reimplantation site after renal transplantation (UVJ), or the diagnosis was unclear. Diagnostic imaging and treatment protocols were not standardized because of the retrospective nature of this study.

Procedures

Information retrieved from the medical records included signalment, history and physical examination findings, clinical laboratory results, urine microbiologic evaluation, and diagnostic imaging findings. All imaging was reviewed by 1 board-certified radiologist (A.C.) for consistency and renal pelvis measurements were standardized based on a transverse ultrasonographic view. Surgical findings and histopathological findings were included when applicable. Short- (<1 month) and long-term (>1 month) outcomes were recorded.

Results

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Therapeutic Intervention
  6. Discussion
  7. Footnotes
  8. References

Signalment

Ten patients met the inclusion criteria. There were 7 domestic shorthairs, 2 domestic longhairs, and 1 Bengal cat. Seven cats were spayed females and 3 were castrated males. The median age at diagnosis was 12 years (range, 5–15 years). The median body weight was 4.6 kg (range, 3.2–6.4 kg).

History and Clinical Signs

Historical findings included previous ureteral surgery in 4/10 cats for ureterolithiasis (median, 428 days; range, 3–940 days). Two cats had evidence of chronic hematuria (>3 months) with no evident cause. They were presumptively diagnosed with essential renal hematuria.

Presenting complaints included anorexia (7/10), lethargy (6/10), vomiting (6/10), diarrhea (3/10), abdominal pain (3/10), weight loss (3/10), hematuria (3/10), and polyuria and polydipsia (2/10). Concurrent medical conditions included urolithiasis (6/10), heart murmur (6/10), chronic kidney disease (3/10), anemia (3/10), suspected essential renal hematuria (2/10), urinary tract infection (2/10), hyperthyroidism (1/10), chronic hepatitis (1/10), and intestinal small cell lymphoma (1/10).

Clinicopathologic Data

The median PCV at presentation was 34% (range, 16–40%; reference, 32–48%). The median blood urea nitrogen (BUN) concentration was 53.5 mg/dL (range, 15–217 mg/dL; reference, 15–32 mg/dL). The median serum phosphorous concentration was 6.9 mg/dL (range, 2.9–17.2 mg/dL; reference, 3.0–6.6 mg/dL). Serum thyroid hormone concentrations were normal in all 6 cats in which they were tested.

The median urine specific gravity at presentation was 1.014 (range, 1.004–1.040; reference, >1.035) with 8/10 cats having a urine specific gravity <1.035. Two cats had positive urine cultures at presentation (Enterococcus and Enterobacter). The median urine pH was 6.75 (range, 5–8.5). Five cats had positive urine dipstick results for blood. No cats had crystalluria on sediment examination and 2 had gross hematuria.

Diagnostic Imaging

Thoracic radiographs were performed in 8/10 cats. Two had a mildly enlarged cardiac silhouette. Two cats had a diffuse bronchiolar pattern, 2 had visible pleural fissure lines, and 1 had an alveolar pattern in 2 lung lobes. Abdominal radiographs were performed on 9/10 cats. Findings included nephrolithiasis (4/10), unilateral small kidney (4/10), unilateral renomegaly (3/10), bilateral small kidneys (2/10), ureterolithiasis (2/10), hepatomegaly (2/10), small intestinal distension (2/10), transitional vertebrae (2/10), decreased abdominal detail (1/10), and hiatal hernia (1/10).

Abdominal ultrasound examination was performed in all 10 cats. All cats had ultrasonographic evidence of ureteral obstruction including ureteral dilatation and renal pelvic dilatation (Table 1). The right ureter was the site of obstruction in 7 patients and the left ureter in 3. The median length of the kidney on the obstructed side was 4.2 cm (range, 2.9–5.4 cm). The median nonobstructed kidney length was 2.75 cm (range, 2.2–4.1 cm). The median diameter of the ureteral dilatation was 4 mm (range, 2.7–13 mm). The distance of the obstruction from the renal pelvis was measured by ultrasound examination in 9/10 cats at the time of diagnosis with a median distance of 3.5 cm (range, 1–6 cm). In the case without this measurement, the obstruction was in the distal ureter at the time of surgery.

Table 1.   Clinical data on feline patients with suspected ureteral strictures.
CategoryCreatinine Preprocedure (mg/dL)Creatinine Periprocedure (mg/dL)Creatinine at Last Recheck (mg/dL)Renal Pelvis Size Preprocedure (mm)Renal Pelvis Size Periprocedure (mm)Renal Pelvis Size at Last Recheck (mm)Location of Stricture to Renal Pelvis (mm)Survival Time (Days)Additional Outcome Information
Median overall3.72.92.311.75 (5.5–23)6 (1.4–11.6)3.39 (0–8)35>294 (range, 14 to >858) (6/10 still alive)MST dead: 131 (range, 14–368) MST alive: >317 (range, 30–858
Median with no intervention (n = 2)2.8 2.410 6.7 >286.5 (range, 14–559)1 still alive
Median with surgery alone (n = 2)10.85 2.18.25 11.6 >822 (range, 786–858)2 still alive (first patients in the series)
Median with stent (n = 6)8.0 3.214.75 2.7 >235 (range, >40–368)3 still alive

Additional ultrasonographic findings included hyperechoic periureteral tissue around the area of obstruction (6/10) (Fig 1), ureterolithiasis in a nonobstructed location (4/10), retroperitoneal effusion (4/10), mesenteric lymphadenopathy (4/10), focal hyperechoic peritoneum (3/10), nephrolithiasis (3/10), hepatomegaly (2/10), liver nodules (2/10), splenomegaly (2/10), an enlarged adrenal gland (2/10), diffuse intestinal muscularis thickening (1/10), jejunal mucosal mass (1/10), and hyperechoic urinary bladder debris (1/10).

image

Figure 1.  (A) Ultrasound image of right kidney and proximal ureter in cat with ureteral obstruction secondary to ureteral stricture. The proximal ureteral dilatation is outlined by yellow calipers and hyperechoic periureteral tissue by red asterisk. (B) Ultrasound image of cat patient who had right sided stricture secondary to circumcaval ureter. This image demarcates caudal vena cava (CdVC) as it crosses ventral to proximal right ureter in area of previous ureteral obstruction. This patient has a stent (white arrowhead) inside the ureter that is decompressing the previously dilated ureter and renal pelvis.

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All 10 cats had some form of a ureteropyelogram. An antegrade ureteropyelogram was performed in 6/10 cats. Three cases were diagnosed as complete obstructions and 3 as partial obstructions (Fig 2). Retroperitoneal leakage of contrast material occurred in 1 cat, and was presumed to be iatrogenic after contrast injection. A retrograde ureterogram was performed in 7 cats during surgical or endoscopic intervention, which documented a site of obstruction with lack of a filling defect in the ureteral lumen in all 7 cats (Fig 2). Diagnostic antegrade ureteropyelography and retrograde ureteropyelography during a therapeutic procedure were in agreement for all patients.

image

Figure 2.  Images (A–D): cranial is to the left and caudal to the right. (A) Antegrade ureteropyelogram of right kidney/ureter by fluoroscopy. The black arrow is identifying ureteral obstruction in proximal right ureter. (B) Antegrade pyelogram through locking-loop nephrostomy tube (white arrow). The black arrow shows blunt obstruction in ureter. (C) Retrograde ureteropyelogram by fluoroscopy/endoscopy showing catheterization of distal ureter (black arrow) and site of obstruction (white arrow). (D) Retrograde ureteropyelogram by fluoroscopy/endoscopy in cat with a proximal ureteral stricture. The black arrow is demarcating site of ureteral stricture. (E) Ventrodorsal radiograph of cat after ultrasound-guided antegrade ureteropyelogram. The black arrow is area of ureteral stricture causing partial obstruction.

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Therapeutic Intervention

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Therapeutic Intervention
  6. Discussion
  7. Footnotes
  8. References

Medical Management

All patients received IV fluid therapy (IVF). Additional medical management was attempted in 6 cats, including nephrostomy tube placement (patients 5, 6, 7, 9),b amitryptiline (patients 4, 6, 7, 9), prazosin (patients 2, 4, 6, 10), and peritoneal dialysis (patient 7). Fluid therapy was maintained for a median of 3.5 days (range, 1–8 days) before further intervention. Two cats had no intervention other than IVF.

Endoscopy

Cystourethroscopy was used in the placement of a ureteral stentc in 1 cat (patient 5).

Surgery

Surgery was performed in 7 cats. One had a ureteral resection proximal to the ureteral stricture and a ureteral reimplantation, 1 had a reimplantation and a ureteral stentc placed, 1 had a ureteronephrectomy, and 4 had a ureteral stent placed by fluoroscopy and surgical assistance (Fig 3). Four patients (4, 7, 8, and 10) had evidence of a circumcaval right ureter at surgery (Fig 1). All were obstructed in the proximal right ureter a few centimeters proximal to the area where the vena cava crossed the ureter.

image

Figure 3.  Cranial is to the left and caudal to the right. Lateral fluoroscopic image of feline patient after double pigtail ureteral stent (black arrowheads) was placed inside the ureteral lumen to bypass proximal ureteral stricture (black arrow).

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Histopathologic Findings

Biopsy specimens of the obstructed ureter was performed in 3 cats. The histopathology was as follows: severe mural granulation tissue with epithelial cell disruption; ulcerative ureteritis with marked transmural fibroplasia and fibrosis and mural histiocytic inflammation; and moderate chronic ureteritis with fibrosis and smooth muscle hypertrophy. None of these lesions was associated with concurrent ureteroliths.

Complications

Procedural-associated complications occurred in 4 patients. These included occlusion of a smaller prototype stent necessitating stent exchange in 2 cats (patients 6 and 8; 17 days and 42 days after placement, respectively), SC ureteral bypass (SUB) in 1 cat because of tissue in-growth 3.5 months after stent placement (patient 7), and restricture after neoureterocystostomy requiring a second reimplantation (patient 4) with no stent placement. In patient 8 in which a stent had been placed by cystotomy, peritoneal effusion occurred for 24 hours after surgery, but a uroabdomen was never definitively diagnosed (serum creatinine concentration, 8.9 mg/dL; fluid creatinine concentration, 8.2 mg/dL).

Minor perioperative complications included fluid overload (3), urinary tract infection (2), pollakiuria (2), and postoperative stranguria (1). None of these cats had clinically relevant echocardiographic heart disease before their associated intervention.

Clinical Outcome

All patients survived to discharge from the hospital. The median duration of hospitalization was 10.5 days (range, 2–23 days). Nine cats had reevaluation of their PCV, total proteins, BUN, creatinine, and electrolyte concentrations before discharge.

Median values after intervention and preceding discharge were as follows: PCV 22.5% (range, 17–33%), BUN 44 mg/dL (range, 23–107 mg/dL), potassium 4.8 mg/dL (range, 3.8–5.8 mg/dL), phosphorus 7.4 mg/dL (range, 3.3–10.4 mg/dL), and albumin 2.4 g/dL (range, 1.5–3.1 g/dL; reference, 2.4–3.8 g/dL).

Four cats (patients 6, 8, 9, 10) developed signs of stranguria or pollakiuria soon after stent placement. These signs were self-limiting at 5 and 10 days, respectively, in 2 patients (patients 8 and 10). Patient 9 continued to have pollakiuria without stranguria that resolved with anti-inflammatory therapy. Patient 6 was euthanized after failure of improvement in azotemia 2 months after surgery and with continued pollakiuria.

Nine cats had renal function reevaluated more than 1 month after discharge (Table 1). Seven cats had at least 1 ultrasound examination of the urinary tract at reevaluation >1 month after their intervention (range, 1–12 months; Table 1). One of these cats was managed medically and the other 6 had stents placed.

Before intervention, 2/10 cats had a urinary tract infection. After intervention, 3 additional cats had at least 1 positive urine culture. Two of these 5 cats had both stenting and surgery performed, 2 had only stenting, and 1 had only surgery (Fig 3). Perioperative urinary tract infection occurred in 1 cat with surgery alone and in 1 cat with surgery, a nephrostomy tube, and stenting. These infections were caused by Escherichia coli and Enterobacter cloacae, respectively, and were appropriately treated with antibiotic therapy. All 4 cats with nephrostomy tubes developed a urinary tract infection either during their hospitalization or after discharge. One cat had 3 positive urine cultures with 3 different bacteria (E. cloacae, Enterococcus sp., and Pseudomonas aeruginosa). Two cats had 2 positive urine cultures (1 with Enterococcus faecium and 1 with Klebsiella pneumoniae and E. faecium).

The follow-up period was highly variable. The median duration of survival after discharge was >294 days (range, 14 to >858 days). Four patients were known to have died 14, 63, 199, and 368 days after discharge. No patient that had an intervention died of a ureteral obstruction and 1/4 died of progressive chronic kidney disease.

Five of 6 patients with stenting procedures had improvement in azotemia and all 6 had reduction in pelvic dilatation after their procedures, including the 3 cats with stent replacement or SUB implantation. Six of 10 patients were known to still be alive at the time of writing this report (median survival time [MST] >317 days). Four of the 6 stented cats were still alive. The patient that had 2 ureteral reimplantations (because of restricture) without stenting did not have improvement in renal pelvis dimension and only minimal improvement in serum creatinine concentration before discharge.

Discussion

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Therapeutic Intervention
  6. Discussion
  7. Footnotes
  8. References

Ureteral strictures are uncommonly recognized in cats, but should be considered a potential cause for ureteral obstructions. The clinical diagnosis can be made with a combination of ultrasonagraphy, ureteropyelography, computed tomography, or surgical exploration. Treatment options include progressive monitoring for partial obstructions, surgical reimplantation, ureteral resection and anastomosis, ureteral stenting, or SUB.

Ureteral strictures appear to occur in middle-aged to older cats, as the median age at presentation in this study was 12 years and the youngest cat was 5 years. Sixty percent of cats had concurrent urolithiasis located at sites other than the site of obstruction. This finding may indicate a predisposition to stricture formation in cats with ureterolithiasis-induced mucosal injury, or that cats with a stricture have decreased urine flow predisposing them to urolithiasis. Forty percent of patients had previous ureteral surgery for ureterolithiasis at the site of the ureteral stricture. Surgical and procedural-induced iatrogenic ureteral strictures have been well described in humans.7–10 Two cats with surgically induced strictures had evidence of a stricture within 5 days of the ureterotomy. The other 2 patients were diagnosed months or years later, suggesting both short- and long-term follow-up by ultrasound examination should be recommended after ureteral surgery.

Two cats had a previous medical history of presumptive essential renal hematuria (patients 3 and 8), although bleeding may have originated from the ureter or blood clots from renal hemorrhage could have caused ureteral damage. This could predispose to strictures because of mucosal damage, inflammation, or clot passage. No blood clot or bloodstone could be identified at the stricture site in either patient. One of these patients had a ureteronephrectomy and a diagnosis of ureteral fibrosis was made on histopathology of the obstructive lesion with no hemorrhagic lesion documented within the renal pelvis or renal parenchyma. The other had a stent placed and no histopathology was performed. Both cases had resolution of the hematuria after intervention.

Anorexia, lethargy, vomiting, and weight loss were the most commonly reported presenting signs. These were comparable to those reported for cats with ureteral calculi,2 and improved after intervention.

Azotemia (80%), hyperphosphatemia (40%), and low urine specific gravity (80%) were the most common clinicopathologic findings, suggesting underlying pathology to the contralateral kidney in most patients. These findings were consistent with reports of ureterolithiasis in which 83% of the cats were azotemic at the time of presentation. No patients demonstrated crystalluria, as compared with 29% of cats in the other study.2

Ureteral strictures have been seen in humans with concurrent circumcaval or retrocaval ureters. A circumcaval ureter can cause external compression of the ureteral lumen as the ureter runs dorsal to the caudal vena cava. This typically occurs during development. The stricture may not be in the exact location as the crossing cava at diagnosis because the ureteral tube migrates during development.12,13 This is reported to predominantly affect the right ureter and is manifested later in life. It can be seen in conjunction with congenital skeletal and soft tissue abnormalities such as supernumerary lumbar vertebrae, portosystemic shunts, partial situs inversus, hypospadias, and intestinal malrotation. This finding is rarely reported in the veterinary literature.12–14 Two cats in this study had evidence of transitional vertebrae on radiographs (patients 7 and 9), and 1 also had a circumcaval ureter.

A circumcaval ureter was found in 4 patients at surgical exploration and 1 of these was also subsequently seen on follow-up ultrasound examination (Fig 1). The prevalence of circumcaval ureter in this series could be underestimated because not all patients were surgically explored. All of these were on the right side in a location similar to that described in humans. Three of 4 of these patients had ureteral stents placed because of the proximal location of the stricture and the expected difficulty for reimplantation. All 3 were doing well at last follow-up. The 4th case had a ureteronephrectomy performed before the availability of ureteral stenting in the authors' practice, and with associated renal hematuria. Because this patient was nonazotemic and had renal hematuria, preservation of the kidney and ureter were considered less imperative at that time. With the advent of newer technology, this patient likely would have been stented.

Ultrasonography consistently demonstrated pelvic and ureteral dilatation ipsilateral to the ureteral stricture. Although the range for distance from the ureter to the site of the stricture was variable, 7/10 (70%) cases had strictures in the very proximal ureter. In this location, a renal descensus and psoas cystopexy or a side-to-end ureteral resection and anastomosis would have been necessary to relieve excessive tension on a conventional surgical anastomosis site. In cases of this report where a ureteral stent was placed, this treatment was considered a safer surgical option by the attending surgeon than the traditional surgical alternative.

Hyperechoic periureteral tissue was seen on ultrasound examination in the area of the stricture in 6/10 cases. This finding has not been reported previously for other causes of ureteral obstruction. If identified, a ureteral stricture should be considered (Fig 1).

Eight patients had concurrent conditions that could be considered possible predisposing factors, including nephroureterolithiasis (6/10), previous ureterotomy (4/10), circumcaval ureter (4/10), presumptive essential renal hematuria (2/10), and urinary tract infection (2/10). The 6 patients with upper urinary tract stones did not have evidence of a stone at the obstructive site in the ureter, but certainly a ball-valve effect could have ultimately caused mucosal damage and ureteral fibrosis. Two cases (patients 2 and 6) could be considered to have had primary strictures, because no underlying cause was identified. Conclusions about prognosis in cats with presumptive primary ureteral strictures are difficult to make based on this small case population.

Treatments were variable based on owner preferences, stricture location, renal function, time of presentation, technology available, and patient history. Ureteral stents were placed in a majority of these cats (6/10). This was because of the fact that most of these patients were referred specifically for ureteral stenting when surgery at a referring institution was deemed risky, not possible, or had failed previously. All of these patients were ill at the time of presentation, necessitating intervention. The 1st stent was placed in a cat in 2006,4 and stenting was not considered an option before this time.

One of the 2 patients that did not have any intervention performed survived. This patient was not ill at diagnosis. The stricture was secondary to a previous ureteral surgery. Because of stability and cost, further intervention was declined by the client.

Indwelling double pigtail ureteral stents are placed in human patients to relieve ureteral obstructions for stones, tumors, and strictures. They are commonly placed either during or after ureteroscopy, ureteral transitional cell carcinoma ablation, ureteral balloon dilatation, or extracorporeal shockwave lithotripsy. Stents in human patients help prevent postprocedural obstruction from edema, recurrent stone passage, or future stricture formation.7–10,15

Pelvic decompression ultimately was accomplished in nearly all patients with stents, including those requiring replacements. The 1 patient with 2 ureteral reimplantation procedures and no stent had a larger renal pelvis before discharge than at presentation. This patient is still known to be alive and free of clinical signs at >858 days, but no follow-up imaging was obtained.

In humans, passive ureteral dilatation is a well-known phenomenon after stenting, allowing placement of a larger stent or endoscope after about 2 weeks.16 In cats, it is expected that there will be some mild pyelectasia so that the loop of the stent can fit inside the renal pelvis (which is approximately 5–7 mm). In the authors' experience, renal pelvis dilatation is typically <5 mm.

Typically, in humans, stents are removed or replaced every 3–12 months to prevent encrustation and infection. Complications in humans from indwelling ureteral stents include stent migration, encrustation, flank pain, dysuria, or hematuria.15,17 In cats, indwelling ureteral stents are tolerated well long term. One case series showed 17/18 stents remained in place and patent long term (range, 2 to >780 days) with no reported need for premature removal. Four cats in that study with stents developed urinary tract infections that were successfully treated with antibiotics.a

In 1 patient, 3.5 months after stent placement, reobstruction was evident. Obstruction was suspected to be from a granuloma that resulted in stent compression and tissue ingrowth. The stent was seen on ultrasound examination to cross the obstruction appropriately with no evidence of stent migration. This patient had a ureterotomy at this site before stricture development and a suture reaction was suspected. Because of the owners' desire to avoid further ureteral surgery, a SUB was performed. The SUB procedure has been described for human patients with end-stage obstructive neoplasia and ureteral necrosis after renal transplantation.18,19 This allows urine to drain from the renal pelvis through the nephrostomy catheter, into the cystostomy catheter, and into the bladder, bypassing the intracorporeal ureter. The complication rates have been reported to be low and human patients have described improved quality of life compared with those with external nephrostomy tubes.18,19 The procedure described in this report was considered a salvage procedure and was patent at the time of writing this report. This procedure has been recently described in more detail in 16 cats.d

The most common complication encountered in this report was urinary tract infection with 5/10 positive cultures posthospitalization and 2 preintervention. Factors predisposing these patients to infection seemed to be the presence of a urinary catheter, urinary tract surgery, ureteral stent, or nephrostomy tubes (4/5). Human patients with ureteral stents are known to develop frequent bacterial colonization of the stent (28%), and Enterococcus spp. seem to be the most common pathogen.20,21 In veterinary patients with ureteral stents and in those that had ureteral surgery without stents, the authors have identified the same pathogen, which has been reported to uncommonly cause a clinically relevant problem (dysuria, fever, and malaise) in humans.22

Uroabdomen has been reported to be the most common complication of ureteral surgery (25% with ureterotomy).3 One cat developed an abdominal effusion (modified transudate) after stenting but the fluid creatinine concentration was not consistent with uroabdomen. This fluid accumulation resolved within 24 hours and did not return. This fluid could have represented postsurgical irrigation fluid, because of low colloid osmotic pressure, or uroabdomen, with additional surgical fluid that diluted the creatinine concentration to a concentration that precluded a diagnosis of uroabdomen.

Ureteral strictures often are discussed, but rarely are reported after feline ureteral surgery. Interestingly, 40% of these patients had a previous ureterotomy at the site of the ureteral stricture, and an additional cat developed a stricture after correction of the first stricture by reimplantation, resulting in 50% of these cats having had a surgical cause for their strictures. Ureteral strictures should be considered an important short- or long-term complication of ureteral surgery.

The fact that 3/6 cats with ureteral stents required either exchange or an alternative procedure is excessive, and clients should be aware that repeated interventions after stent placement may be necessary if this is the treatment chosen. The stents placed in these cats were not all multifenestrated and were of various stiffness and size (1.9–3.0 French). This study represented a time when ureteral stenting in cats was in its very early stages and prototypes of various materials were being investigated clinically. With the newer, smaller, multifenestrated double pigtail stents, and more biocompatible material,c the need for stent exchange appears to be less common in the authors' experience. Regardless, stents always should be monitored for long-term problems, as should animals after traditional ureteral surgery.

The median hospitalization of 10.5 days could be because of the relative chronicity and severity of these obstructions, resulting in prolonged periods of postobstructive diuresis and the need for very careful fluid management. The 1 patient that was hospitalized for over 20 days was not typical; it was extremely ill and experienced the longest postobstructive diuresis. Monitoring central venous pressure, body weight, clinical hydration status, and other laboratory variables is recommended. Regardless of management, 3 patients developed fluid overload within 3 days of their procedures.

Three of 8 patients that had some attempt to relieve their ureteral obstruction died for reasons unrelated to treatment or underlying ureteral disease. All died as a consequence of causes other than inability to relieve their urinary obstruction. Patient 5 died after presenting with severe leukopenia and hyperbilirubinemia. At this time, serum creatinine concentration was 2.1 mg/dL, with < 2 mm pelvic dilatation, and a negative urine culture. Patient 6 became progressively more azotemic, but showed resolving pelvic dilatation after stenting. We suspect that progression of chronic kidney disease was the cause of death. Patient 8 developed congestive heart failure secondary to cardiomyopathy, and was euthanized with a stable serum creatinine concentration and minimal renal pelvic dilatation 1 year after ureteral stent placement. In all patients, MST was >294 days (range, 14 to >858 days).

In dogs, complete recovery of glomerular filtration rate can occur when ureteral obstruction is relieved within 4 days, but <50% recovery occurs after 2 weeks, and no recovery is seen after 40 days.3 Based on these data, early intervention should be strongly encouraged. With the difficulty of treating ureteral strictures in cats by traditional surgical techniques, particularly for very proximal locations, the advent of newer interventions may help circumvent this dilemma and treat these patients more quickly. The technology is evolving with better equipment, making this procedure safer and more effective. More research is needed before this approach can be definitively recommended.

There are several limitations of this study. The retrospective nature and small sample size make it difficult to determine the advantages and disadvantages of medical, surgical, and interventional treatments. The patients of this study had strictures that were in various locations, some complete and some partial, making it difficult to compare the surgical technique to the stenting technique as they were done for different locations and different reasons. Some patients were either minimally azotemic or nonazotemic making chronic monitoring or ureteronephrectomy reasonable alternatives to more aggressive intervention. Comparing outcomes of medical versus surgical and interventional approaches is not possible. The stents used in this study were not the currently available ureteral stents currently being used routinely in the authors' practice, so one might expect different tolerance and need for exchange at this point in time. Also, the long- and short-term follow-up was variable in each patient.

The fact that stents were well-tolerated long term once an appropriate stent was placed, with ultimately good outcomes, suggests that stenting is a consideration in cats with ureteral strictures in any location, particularly when surgery is too difficult or not an option. Owners should be informed that stents are associated with their own risks such as infections, reactions, migration, UVJ reflux, and pollakiuria (typically short term) and owners must be aware of these complications. The authors do not necessarily recommend that stenting replace surgery, but stenting should be considered as a new less invasive option. The complications seen with stents typically are not life threatening and because of passive ureteral dilatation a few days after a stent placement, stent exchange, when necessary, can be performed as an out-patient procedure, unlike a restricture after traditional surgery. As data regarding the long-term risks of ureteral stents become available, this procedure may become more routinely recommended, but at this time it is still considered investigational.

In conclusion, ureteral strictures should be considered as a cause of ureteral obstruction in cats. Strictures can be seen in cats with previous ureteral surgery, concurrent ureterolithiasis, essential renal hematuria, or circumcaval ureter. Strictures are more commonly found in the proximal right ureter and often are associated with ultrasonographic hyperechoic tissue surrounding the ureter. With appropriate surgical or interventional treatment, and the potential need for multiple procedures, the long-term prognosis can be good with a median survival of over 294 days. Ureteral stenting or SUB may be considered safe and effective alternatives to surgical management, but more research is necessary.

Footnotes

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Therapeutic Intervention
  6. Discussion
  7. Footnotes
  8. References

a Berent A, Weisse C, Bagley D, Adan C, Todd K, Solomon J. Ureteral stenting for feline ureterolithiasis: Technical and clinical outcomes. Proc ACVIM Forum 2009;686 (abstract)

b Dawson-Meuller, 5 french Locking-loop pigtail catheter, Cook Medical, Bloomington, IN

c 0.018 in. Weasel wire, Infiniti Medical LLC, Malibu, CA

d Berent A, Weisse C, Bagley D. The use of a subcutaneous ureteral bypass device for ureteral obstructions in cats. Vet Surg 2010; 39:E30 (abstract)

References

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Therapeutic Intervention
  6. Discussion
  7. Footnotes
  8. References
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