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- Materials and Methods
- Therapeutic Intervention
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.
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.
- Top of page
- Materials and Methods
- Therapeutic Intervention
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.