Ureteral agenesis is the congenital absence of one or both ureters due to incomplete ureteral bud formation. Unilateral ureteral agenesis is the most common form observed in dogs and cats and is usually accompanied by ipsilateral renal aplasia ().
Ureteral duplication is a congenital disorder involving complete or partial duplication of one ureter. This disorder has been associated with a duplexed kidney and a supernumerary kidney in dogs; ureteral duplication has not been observed in cats ().
Congenital ureteral valves are persistent transverse folds of vestigial mucosa and smooth muscle fibers forming annular, semiannular, or diaphragmatic lesions in the ureter (). Semiannular ureteral valves have been described in a 6-month-old female collie with unilateral ureterectasis, hydronephrosis, and urinary incontinence (). The etiopathogenesis of urinary incontinence associated with ureteral valves in this case is uncertain.
Ureteral ectopia is a congenital anomaly in which one or both ureters terminate abnormally in the urinary bladder. Intramural ectopic ureters contact and enter the bladder wall normally but continue submucosally through the trigone and terminate distally in the urethra or vagina (). Intramural ectopic ureters may also form ureteral troughs, develop double ureteral openings, or fail to develop a distal orifice. Extramural ectopic ureters totally bypass the bladder before terminating in the urethra, vagina, or uterus (). Female puppies and kittens are affected more often than males). Most ectopic ureters in female dogs are unilateral (). In male dogs, unilateral and bilateral ureteral ectopia appear to occur with similar frequencies. The urethra is the most common site of ectopic ureters in female dogs. In males, the prostatic urethra is the most common site of termination. Because of the close relationship between the metanephric duct system and development of the urogenital organs, ectopic ureters may be associated with other concurrent anomalies such as renal ectopia, renal hypoplasia, renal aplasia, ureteroceles, urachal remnants, urinary bladder, agenesis or hypoplasia, urethral agenesis or ectopia, phimosis, and persistent hyman ().
Although most cases occur in mixed-breed dogs, an increased frequency of ectopic ureters has been found in Siberian huskies, Labrador retrievers, Newfoundlands, English bulldogs, West Highland white terriers, fox terriers, golden retrievers, Skye terriers, Welsh corgis, and miniature and toy poodles (). Familial or breed predilections have not been identified in cats with ectopic ureters. Clinical signs of urethral ectopia vary, being dependent on the site of termination of the abnormal ureter and other urogenital abnormalities. Urinary incontinence is the predominant clinical sign. Ureteral ectopia is often recognized shortly after weaning, and its severity may vary from continuous involuntary dribbling to intermittent incontinence associated with rest, excitement, or changes in body position (). Discoloration of the periurethral hair and urine scald dermatitis may also be observed.
Table Causes of Urinary Incontinence in Immature Dogs
- Spinal dysraphism
- Spinal trauma
- Anatomic anomalies
- Ureteral ectopic
- Ureteral ectasia
- Ureteral valves
- Urinary bladder agenesis/hypoplasia
- Urinary bladder duplication
- Ectopic uterine horns
- Colorurocystic fistula
- Patent urachus
- Urethral agenesis
- Urethral hypoplasia
- Obstructive (paradoxical) incontinence
- Urethral stricture
- Periurethral mass lesion
- Urge incontinence
Inappropriate (submissive) micturition
Table Problem-Specific Database for Urinary incontinence in Immature Dogs
- Medical history
- Note age, sex, and breed
- Note owner’s definition of incontinence
- Note age of onset and duration of incontinence
- Physical examination
- Observe micturition
- Evaluate bladder size before and after micturition
- Verify incontinence
- Vaginal examination
- Neurologic examination
III. Quantitative urine culture
- Serum biochemistry (serum urea nitrogen and creatinine = minimum)
- Survey abdominal radiographs
- Excretory urography
- Contrast urethrography or vaginography
- Endoscopy (vaginoscopy, urethroscopy, cystoscopy)
Although urinary incontinence in immature animals is highly suggestive of ectopic ureters, other causes of incontinence should be considered (Tables Causes of Urinary Incontinence in Immature Dogs and Problem-Specific Database for Urinary incontinence in Immature Dogs). Excretory urography combined with retrograde contrast urethroggraphy or vaginography appears to provide the most comprehensive means of establishing a definitive diagnosis (). In addition, vaginoscopy, urethroscopy, and cystoscopy may allow direct visualization of an ectopic ureteral orifice (). Urinary incontinence associated with ectopic ureters is helped only with surgery. Surgical strategies employed for correction of ectopic ureters include transection and reimplantation of the ureter, creation of a neostoma in situ, or complete removal of the kidney and its ureter. Dogs with postoperative incontinence due to urethral insufficiency may benefit from pharmacologic management with a-adrenergic agonists such as phenylpropanolamine.
A ureterocele is a congenital cystic dilation of the terminal submucosal segment of the intravesicular ureter. Orthotopic (simple) ureteroceles are located at the trigone of the urinary bladder with the ureteral orifice in normal position. Ureteroceles accompanying ectopic ureters are classified as ectopic ureteroceles. Ureteroceles may be unilateral or bilateral and are typically ectopic (). Most ureteroceles have been observed in female puppies. Ureteroceles have not been reported in kittens. Puppies with orthotopic ureteroceles may be asymptomatic or may develop signs of lower urinary tract disease (i.e., dysuria, stranguria, pollakiuria, and hematuria). Puppies with ectopic ureteroceles typically develop urinary incontinence. A diagnosis of ureterocele is based on excretory urography, ultrasonography, and / or exploratory celiotomy and cystotomy. Treatment of ureteroceles is directed at alleviating clinical signs by ureterocelectomy or ureteronephrectomy and eliminating and/or preventing urinary tract infections.
Vesicoureteral reflux is retrograde flow of urine from the bladder into the ureters and renal pelves. Primary vesicoureteral reflux denotes intrinsic maldevelopment of the ureterovesical junction; the term secondary vesicoureteral reflux implies an acquired disorder of the ureterovesical junction. Primary vesicoureteral reflux occurs in 79% of healthy puppies 2 to 4 months of age and in 47% of healthy puppies 4 to 6 months of age (). As puppies mature, the frequency of primary vesicoureteral reflux decreases and is observed in less than 10% of adults. The cause of primary vesicoureteral reflux is unknown; however, it is believed to be related to delayed maturation of the vesicoureteral junction. Vesicoureteral reflux may also occur secondarily to urinary tract infection, congenital anomalies of the bladder and urethra (ureteral ectopia, ureteral duplication, and urinary bladder diverticula), urethral obstruction, and neurogenic bladder diseases (). A diagnosis of vesicoureteral reflux is based on contrast radiography, preferably voiding or maximum distention retrograde contrast cystourethrography.
Selections from the book: “Veterinary pediatrics: dogs and cats from birth to six months”. Johnny D. Hoskins. (2001)