Ectopic Ureterocele in a Cat

Introduction

A ureterocele is a focal dilatation of the distal ureter.¹ In humans, the dilatation often occurs in the submucosal segment of the ureter within the bladder wall (i.e., intravesical).² This type of dilatation is also described in dogs.³ A ureterocele may also occur in association with an ectopic ureter (i.e., ectopic ureterocele).⁴ An ectopic ureterocele is a dilatation in which some portion of the ureterocele is situated at the bladder neck or in the urethra.⁴ Ureteroceles have been described in dogs, but to the authors’ knowledge, they have not been reported in cats.^3,5–13

Most dogs with an ectopic ureter and/or ureterocele are presented for urinary incontinence without concomitant renal abnormalities.⁶ Neoureterocystostomy is the most commonly performed surgical correction for ectopic ureters in the dog.^5,11,12 Neoureterocystostomy, as well as marsupialization of the ectopic ureterocele and ligation of the distal communication of the ureterocele with the ureter have been reported to treat urinary incontinence in dogs with an ectopic ureter and ectopic ureterocele.¹¹ There are no published cases of intravesical ureter anomalies in cats. As compared to dogs and humans, all reported cases of abnormal ureters in cats are ectopic (i.e., they terminate caudal to the bladder).^14–18 The purpose of this report is to describe the diagnosis and surgical modification of an ectopic ureterocele in a cat, resulting in postoperative urinary continence.

Case Report

A 9-month-old, 4.5-kg, castrated male domestic shorthair cat was presented to the referring veterinarian with a history of chronic urinary incontinence that was first noted at 5 months of age. Polydipsia and polyuria were present before incontinence was noticed. A 10-day course of amoxicillin/clavulanic acid was prescribed but resulted in only mild improvement in incontinence. A complete blood count and partial serum biochemical panel were unremarkable. Urinalysis was unremarkable except for a urine specific gravity of 1.063 (reference range 1.025 to 1.060), microscopic hematuria, and a sediment that included 3+ magnesium-ammonium-phosphate crystals. The urine was not cultured. Another course of amoxicillin/clavulanic acid was given for 2 weeks. The urinary incontinence did not resolve, and the cat began to show signs of perineal irritation (e.g., licking his penis excessively). An excretory urogram [Figures 1A, 1B] revealed severe, right-sided hydronephrosis and a tortuous hydroureter. An oblong-shaped structure filled with contrast was situated dorsal to the urethra and extended from the bladder neck to the cranial half of the pelvic urethra. The cat was referred for a surgical consultation at the Veterinary Specialty Hospital of San Diego (VSHSD).

On initial presentation to VSHSD, the cat continuously dribbled urine in the examination room. The rest of the physical examination was unremarkable. A serum biochemical panel revealed low concentrations of blood urea nitrogen (15 mg/dL; reference range 16 to 32 mg/dL); creatinine (0.7 mg/dL; reference range 0.7 to 1.9 mg/dL); calcium (8.2 mg/dL; reference range 9.1 to 10.5 mg/dL); total protein (4.7 g/dL; reference range 6.0 to 7.9 g/dL); albumin (2.5 g/dL; reference range 2.5 to 3.7 g/dL); and globulin (2.2 g/dL; reference range 2.5 to 4.7 g/dL). A urine sample collected by cystocentesis showed the urine was orange and cloudy. The urine specific gravity was 1.045, and pH was 6.0. There were 0 to 3 white blood cells per high-power field, and red blood cells were too numerous to count. The aerobic bacterial culture of the urine was negative.

Celiotomy was performed via a ventral midline approach to the caudal abdomen. The bladder was distended with urine. A second sample of urine was collected by cystocentesis and submitted for bacterial culture. The normal left ureter was seen entering the bladder at the trigone. The right ureter was dilated, tortuous, and thickened. The right ureter bypassed the bladder and terminated in a dilatation associated with the proximal urethra. The right ureter was surgically transected just proximal to the ureterocele. Urine excretion from the right ureter was immediately evident. A ventral cystotomy and neoureterocystostomy were performed as described by Gregory et al.¹⁹

The bladder mucosal surface had several areas that were erythematous and irregular. A no. 5 polyvinyl catheter^a was easily passed into the urethra from the bladder to allow identification of the patent urethra ventral to the ureterocele. A partial ureterocelectomy was performed by excision of the cranial one-third of the ureterocele. A proximal communication of the ureterocele to the urethra was identified and ligated. The excised portion of the ureterocele was submitted for histopathology. The ureterocele was incised and explored as far caudally as possible, but because of the small caudal abdomen and proximal pelvic canal, it was necessary to ligate the ureterocele distally without visually identifying the distal opening into the urethra. Routine closure of the bladder and abdomen was performed.

For the first 12 hours after surgery, urinary incontinence continued, and the cat had gross hematuria. Over the next 24 hours, the hematuria diminished, although the incontinence continued. The intraoperative urine sample was negative for bacterial growth. Amoxicillin/clavulanic acid was continued orally because of the compromised mucosal surface of the bladder.

Histopathology of the ureterocele tissue revealed widespread edema and vascular congestion within the submucosa. The muscular layer was discontinuous, which may have indicated incomplete development. The transitional epithelium was normal and was consistent with a ureteral origin.

Two weeks later, a serum biochemical panel, urinalysis, and urine culture were reevaluated. The chemistry values were within normal limits. Urinalysis was normal, and the urine culture was negative. Antibiotics were discontinued. An excretory urogram [Figure 2] revealed improvement in the right-sided hydronephrosis and hydroureter. The terminal portion of the right ureter was superimposed over the body of the bladder where it was implanted. Persistent distention of the partially excised ectopic ureterocele was visualized radiographically, but the cat was no longer incontinent.

Approximately 8 months after surgery, a retrograde urethrogram was performed to further evaluate any persistent dilatation of the ureterocele. The urethrogram showed concurrent filling of the urethra, bladder, and the remnant of the ectopic ureterocele [Figure 3]. It was assumed that the filling of the remaining ureterocele occurred at its distal communication with the urethra. Although this was a site of potential urine pooling, no secondary clinical signs were noted.

Discussion

Urinary incontinence is much rarer in cats than in dogs.^3,14 The most common congenital cause of urinary incontinence in the cat has been ureteral ectopia.^14–18 In general, ectopic ureters result from failure of normal differentiation of the mesonephric and metanephric ducts.^2,20 Ectopic ureters have been reported in 23 cats.^14–18 The most common concurrent abnormalities were hydronephrosis and hydroureter.^14–18 Urinary continence has occurred postoperatively in cats treated with neoureterocystostomy.¹⁴ In a review of 19 cases of congenital urinary incontinence, 13 cats with ectopic ureters were incontinent before neoureterocystostomy, and 12 (92%) of the 13 were continent after the procedure.¹⁴ The cat in this case report was continent postoperatively.

In humans and dogs, ureteroceles associated with aberrant ureters have been reported.^1–13,20 Based on their anatomical locations, ureteroceles may be intravesical or ectopic in the dog.^5–13 An intravesical ureterocele is a cystic dilatation in the submucosa within the bladder wall and is the most common type in dogs and humans.^1–13,20 A classification scheme for canine ureteroceles has been proposed by Stiffler, et al.⁵ Ureteroceles in dogs are graded 1 to 3 based upon functional characteristics.⁵ Grade 1 ureteroceles are defined as having no evidence of upper urinary tract disease.⁵ Grade 2 ureteroceles have concurrent ipsilateral hydroureter, hydronephrosis, or chronic renal disease.⁵ Grade 3 ureteroceles have concomitant bilateral hydroureter, hydronephrosis, or chronic renal disease.⁵ Within each grade, the ureterocele can be further classified anatomically as either intravesical or ectopic.⁵

The proposed classification scheme for canine ureteroceles can be extrapolated to classify the urinary tract anomaly in this cat.⁵ An intravesical location in the cat has not been reported, and thus a grading system describing functionality alone would be sufficient. In the cat of this report, ipsilateral hydronephrosis and hydroureter were present without azotemia, owing to a functioning left kidney. Based on these findings, the ureterocele would be considered grade 2. These classifications might be useful to grade ectopic ureters and concurrent functional urinary tract changes in the cat. A formal classification system for feline ureteroceles may facilitate comparison of future cases in the veterinary literature.

The embryology of ureteroceles has been debated in the human medical literature.^1–2,20 One theory suggests an incomplete breakdown of the ureteral bud and mesonephric duct, causing an obstruction leading to the formation of a ureterocele.² Another author theorizes an intrinsic muscular deficit may cause ureterocele formation.²⁰ No single theory can explain all types of ureteroceles in all species. The fact that all feline ureteroceles reported are ectopic rather than intravesical, as compared to humans and dogs, perhaps implies a single pathogenesis for this rare defect in cats.

Conclusion

Unilateral ureteral ectopia and an ectopic ureterocele were diagnosed as the causes for urinary incontinence in a 9-month-old cat. Neoureterocystostomy was successful in eliminating the urinary incontinence, although radiographically persistent urine pooling occured in the remnant of the ureterocele.