Chapter 81 Diseases of the Urethra
CONGENITAL URETHRAL DISORDERS
Etiology
• Rectal urethral fistula is due to incomplete division of the embryonic cloaca into the cranial ureterovesicular segment and the caudal rectal segment by the urorectal fold. This condition is thought to be heritable in the bulldog, but is thus far unproven.
• Urethral hypoplasia is often associated with uterine hypoplasia and vaginal aplasia with the uterine horns terminating in the dorsum of the urinary bladder. This is also called congenital urethral sphincter mechanism incompetence. Urinary incontinence occurs in almost all cases of this anomaly.
• Urethral hypospadias is often associated with pseudohermaphroditism, true hermaphroditism, in utero exposure to androgen inhibitors or estrogens, and inadequate production of androgens by the fetal testes. The result is incomplete fusion of the urethral groove resulting in the urethral opening occurring on the ventral aspect of the penis and prepuce. This defect occurs in combination with penile hypospadias and a bifid scrotum.
• Other congenital urethral anomalies include urethral duplication, urethral agenesis, dilation/diverticulum of the pelvic urethra, urethral stricture and stenosis, urethral ectopia, accessory meatus, anterior or posterior urethra valves, and penile anomalies that secondarily affect the urethra such as apenia, megalopenis, and micropenis.
Clinical Signs
• In animals with a rectal urethral fistula, urine exits from the rectum, which may result in loose fecal material or diarrhea.
• Some urethral anomalies such as stricture and hypoplasia/aplasia result in signs of lower urinary tract outflow obstruction and potentially uremia.
Diagnosis
• Many of the congenital urethral abnormalities are visible on physical examination or vaginal examination.
• Retrograde urethrogram or a vaginourethrogram can further locate and define the nature and extent of the abnormality. Voiding cystourethrography can also be a useful diagnostic modality (see Chapter 4).
Treatment
• Correct urinary obstruction to stabilize the animal prior to additional diagnostics and treatment.
• Surgical correction of rectal urethral fistulas, hypospadias, strictures, urethral duplication, urethral dilation or diverticulum, and urethral hypoplasia can be attempted. Outcome of surgical intervention for these disorders is complicated and can be unrewarding or associated with a variety of complications, especially if not performed by a surgeon with advanced training.
URETHRAL OBSTRUCTION
Etiology
• Complete or partial obstruction of the urethra is commonly encountered in veterinary practice. Almost any type of disease that affects the urethra can result in some degree of urethral obstruction. There are two classes of urethral obstruction: structural and functional.
• Structural urethral obstruction is caused by anything that physically blocks the urethral lumen or compresses the urethral lumen from outside the urethra. Common examples include urethral calculi, neoplasia, mucous plugs, blood clots, and compression from external trauma to the pelvis area or lymphadenopathy. Strictures are also classified as a structural urethral obstruction. Inflammatory processes such as urethritis may result in swelling of the mucosa of the urethra that results in obstruction.
Clinical Signs
• With partial obstruction stranguria, pollakiuria, dysuria, hematuria, inappropriate urinations, and urine dribbling may occur.
• Complete urethral obstruction results in signs of uremia within a few days of the obstruction. The owners may note that the animal makes frequent attempts to urinate, but produces no urine.
Diagnosis
Physical Examination
• On physical examination the urinary bladder may be by distended, turgid, and painful on palpation.
• It may or may not be possible to manually express the urinary bladder to determine urethral patency. Perform this procedure carefully to avoid urinary bladder rupture.
• Exteriorize the penis to evaluate occlusion at the tip of the penis. Masses, calculi, and urethral plugs can be present in this location, causing obstruction, and are often overlooked on the initial examination.
Complete Blood Count and Serum Chemistry Profile
• Blood should be submitted for a complete blood count and serum biochemical profile testing. Animals with complete urinary obstruction may have life-threatening metabolic abnormalities such as hyperkalemia, metabolic acidosis, and azotemia that require immediate attention.
Treatment
Patient Stabilization Measures for Urinary Obstruction
• Place an indwelling intravenous catheter. Patient stabilization and treatment of metabolic abnormalities take precedence over decompression of the urinary bladder.
• Begin rehydrating the patient with a potassium-free fluid such as 0.9% NaCl until the serum potassium status is known. Animals that have complete urinary obstruction frequently have severe dehydration and may experience hypovolemic shock. Adjust the fluid therapy to meet the patient needs.
• If bradyarrthymias and sinoatrial standstill secondary to hyperkalemia are present, use the following measures to drive the potassium back into the cells thereby lowering serum potassium:
• Administer 0.9% NaCl. This will often normalize the serum potassium following relief of the obstruction if the serum potassium is 7 mEq/L or less.
• Sodium bicarbonate given intravenously (IV) over 5 to 10 minutes at a dose of 0.5 to 1 mEq/kg. If necessary, then infuse an additional 1 to 2 mEq/kg slow IV over 30 to 60 minutes. This will rapidly decrease serum potassium and maintain it for several hours.
• Consider 20% dextrose at 1 to 2 ml/kg IV over 30 to 60 minutes. This can be followed with regular insulin at 0.2 to 0.4 U/kg IV and 50% dextrose at 4 ml/unit of insulin slow IV. Dilute the 50% dextrose to a 2.5% to 5% solution.
• Consider 10% calcium gluconate at 0.2 to 0.5 ml/kg IV over 15 minutes while monitoring an ECG to provide cardioprotective effects from the hyperkalemia. This treatment alone does not lower serum potassium; one of the above-listed treatments is additionally required.
Relief of the Urethral Obstruction
• After appropriate medical stabilization, place a urinary catheter to decompress the bladder and relieve the obstruction. If sedation or anesthesia is necessary for this procedure, care should be taken in drug selection as these patients are commonly volume depleted and have cardiovascular compromise.
• Urethral hydropropulsion is generally required to push urethral calculi back into the urinary bladder (see discussion later in this chapter). Rigid polypropylene catheters are most useful in the initial decompression of the urinary bladder, but should be replaced by softer and less reactive catheter material for indwelling use. Red rubber, Silastic, and silicone materials are superior for indwelling use. Place an Elizabethan collar on the animal after the indwelling urethral catheter has been placed and secured.
• Cats with urinary blockage due to urethral plugs or calculi do not commonly have associated urinary tract infection. Therefore, empirical use of antimicrobials in cats with urethral plugs is not warranted. Administer antimicrobial treatment if the urine culture is positive for bacteria. If urine was not obtained for culture at the time the cat was unobstructed, obtain samples for culture at the time the urinary catheter is removed. Use empirical or prophylactic antimicrobials only in cases of urinary obstruction that have clinical signs of urosepsis which are supported by findings on the urinalysis.
• Maintain a closed urinary system and measure urine output every 4 to 6 hours. Handle all connections to the urinary catheter and closed collection system in a sterile manner to prevent nosocomial infection. Measuring urine output is important since post-obstruction diuresis is common. Quantifying urine output will help determine intravenous fluid therapy dosages and alert the clinician if oliguria or anuria is a problem (see Chapter 5).
• To guard against reobstruction, maintain the indwelling urinary catheter until the animal is taken to surgery for surgical removal of the retropulsed calculi. In cases of feline urinary obstruction where a urethral plug is removed, maintain the catheter for 24 to 48 hours. Administer medications to relieve urethral spasm (acepromazine 0.05–0.1 mg/kg IM, IV, or SC q6–8h) and pain (butorphenol 0.2 mg/kg IM, IV, or SC q6–8h). If the cat can produce a good urine stream post obstruction, had not been obstructed for a prolonged period, and had minimal particulate matter flushed out of the urethra and/or bladder, an indwelling urinary catheter is not necessary.
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