Congenital Disorders of the Urinary Tract

Chapter 105

Congenital Disorders of the Urinary Tract

Emily A. Graves

Although congenital malformations of the equine urinary tract are rare, anomalies affecting all portions of the tract have been reported. Some defects are revealed in neonatal foals, whereas others are discovered incidentally at postmortem examination of mature horses. Abnormalities include ectopic ureters; patent urachus; renal agenesis, hypoplasia, or dysplasia; polycystic kidneys and renal cysts; bladder defects; pendulant kidney; rectovaginal or rectourethral fistulas; ureteral defects; and vascular anomalies.

Ectopic Ureter

Ectopic ureters result from abnormal embryologic development of the mesonephric or metanephric ducts and tissue. Ectopic ureters specifically result from failure of the metanephric duct to (1) migrate cranially to the trigone of the bladder or (2) be incorporated into the urogenital sinus. Also, in fillies, failure of regression of the mesonephric duct or ducts leads to opening of the ureter or ureters into the uterus or vagina. In colts, the mesonephric ducts develop into the Wolffian duct system of the reproductive tract.

The most common clinical presentation is a filly with a lifelong history of urinary incontinence and concomitant hindlimb urine scalding. A true sex predilection has not been proven, but some studies suggest that fillies are affected more commonly. This may represent the fact that normal retrograde flow of urine in colts from the pelvic portion of the urethra to the bladder makes incontinence a less common complaint. Affected males tend to present with a history of chronic urinary tract infections.

Diagnosis relies on visual speculum examination in fillies; endoscopic examination of the urethra, bladder, and vagina (in fillies); and contrast radiography. Examination should determine whether the condition is unilateral or bilateral. Endoscopy is often adequate for determining the location of the ectopic ureteral opening. In addition, dye injection into the bladder or intravenously can help the examiner identify the source of urine flow by use of endoscopy.

Occasionally, radiographic studies are required to localize the opening or openings. Options include contrast retrograde cystography or urethrography, intravenous urography, and intravenous pyelography. The latter two options pose a challenge in older animals because adequate radiographic technique may not be achievable; but when possible, these radiographic tests can provide useful detail of the upper urinary tract before surgery. Other important diagnostic tests are renal ultrasonography, complete blood count, serum chemistry profile, urinalysis, and urine culture. With ultrasonography or radiography, common abnormalities found in association with ureteral ectopia include hydroureter and hydronephrosis on the affected side. Appropriate treatment for urinary tract infections must be completed before surgical intervention is undertaken. Contralateral kidney function can be assessed with blood work (blood urea nitrogen and creatinine), measurement of glomerular filtration rate, excretory urography, and nuclear scintigraphy.

Treatment options include surgical reimplantation of the ureters into the bladder wall. Surgical techniques described include (1) submucosal tunneling of the ureter followed by establishment of a new ureteral opening near the trigone of the bladder and (2) side-to-side anastomosis of the ureter and dorsolateral bladder wall. In both instances, concerns with ascending pyelonephritis will remain for the life of the animal. With bilateral disease, a normal micturition response and adequate urethral sphincter competence should be documented before surgery. In addition, in cases of unilateral ectopia, unilateral nephrectomy is a proven and realistic treatment option. Normal function in the contralateral kidney should be established before nephrectomy. Several case reports describe the technique and documented successful outcomes. The major complications associated with these techniques are residual nonfunctional ureteral openings, hemorrhage, postoperative peritonitis, and postoperative adhesion formation.

Patent Urachus

In the fetus, the urachus serves as the connection from the bladder to the allantoic fluid space and allows for passage of accumulated fetal urine. Normally, the urachus closes at birth and regresses to form a scar. In neonates, a patent urachus may be congenital or develop as a secondary complication in cases of failure of passive transfer or septicemia. The etiology of the congenital form is poorly understood. Multiple theories have been proposed, including an association with umbilical cord length or cord torsion. Patency secondary to omphalitis or omphalophlebitis is the most common scenario observed in foals. Clinical signs include urine leaking from the umbilicus sporadically or during micturition, a persistently moist umbilicus, and pollakiuria. Septic foals should be monitored daily for signs of patent urachus and ruptured bladder with ultrasonography. Septic foals may develop patent urachus even in the face of several days to weeks of hospitalization and antimicrobial treatment.

Some clinicians recommend topical application of various chemical agents to cauterize the patent urachal remnant. Options include dilute iodine or chlorhexidine solutions, concentrated phenol solution, or silver nitrate application. Although many breeding farms perform this treatment prophylactically, these agents can be irritating to the umbilical stalk and surrounding skin. This may in fact potentiate development of omphalitis or omphalophlebitis. If the problem persists or umbilical infection is concurrently present, surgical resection is indicated. This procedure typically involves removal of the urachus and a small portion of the apex of the bladder.

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Jul 8, 2016 | Posted by in EQUINE MEDICINE | Comments Off on Congenital Disorders of the Urinary Tract
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