Chapter 82 Surgery of the Urethra
Urethral disorders in dogs and cats frequently result in partial or complete obstruction. Emergency care may be required to restore the flow of urine and to treat metabolic imbalances. Calculi within the urethra are often accompanied by urinary tract infection (UTI) and cystic calculi. Aggressive medical and dietary management is required after surgery to prevent recurrence. Be careful during surgical manipulation of the urethra to minimize the potential for postoperative scar tissue formation and subsequent urethral obstruction.
ANATOMY
Male Canine Urethra
• The urethra in the male canine is divided into three parts: the prostatic, membranous, and cavernous or penile portions.
• The urethral sphincter is not a discrete structure in the dog. Urethral pressure profiles demonstrate a zone of increased pressure that extends from the prostatic urethra into the membranous urethra. Of the components of the urethral sphincter closure mechanism (fibroelastic tissue, smooth muscle, striated muscle), smooth muscle is probably primarily responsible for maintaining tone in the resting state. Therefore, alpha-adrenergic agonists may be successful in the treatment of sphincter mechanism incompetence.
• The smooth muscle of the urethra is innervated by autonomic nerves arising from the pelvic plexus. The striated musculature receives innervation from branches of the pudendal nerve.
• The distal portion of the penile urethra lies within the os penis. Dilation of the urethra is limited within the os penis and in the perineal portion of the urethra, as it curves around the ischium. These are common locations for calculi to become lodged within the urethra.
Male Feline Urethra
• The male feline urethra consists of three parts: (1) the preprostatic, which lies between the bladder and the prostate gland and is relatively longer than the corresponding portion of the male canine urethra; (2) the prostatic part, which extends from the prostate to the bulbourethral glands; and (3) the penile urethra. Immediately caudal to the bulbourethral glands, the urethral lumen rapidly narrows from approximately 4 mm in diameter to 1 mm. This diameter is maintained through the remainder of the penile urethra. When the penis is retracted, the prostatic and proximal penile urethra may assume the appearance of a flattened or gentle “s,” which complicates urethral catheterization unless the penis is manually extended.
• An area of increased pressure thought to correspond to the sphincter mechanism is found in the urethra caudal to the prostate. Despite a decrease in intraurethral electromyographic activity after perineal urethrostomy (PU) in male cats, urinary incontinence is an uncommon occurrence. This may be due to the smooth muscle fibers as well as the remaining striated fibers of the urethral sphincter, which results in resting urethral pressure greater than intravesicular pressure during bladder distension.
Female Canine and Feline Urethra
• The urethra in the female dog and cat is relatively short in comparison to the male and corresponds to the portion of the male urethra found cranial to the level of the mid-prostate. The female urethra is also relatively larger in diameter and more distensible than the corresponding male urethra.
• It appears unlikely that a discrete urethral sphincter is present in either dogs or cats. The urethral pressure profile does not demonstrate a discrete increase in pressure, but the major increase in urethral pressure develops in the mid-urethra of the female dog. A localized area of increase in urethral pressure has been observed in female cats associated with striated musculature near the external urethral orifice.
• The female urethra is innervated by autonomic fibers of the hypogastric and pelvic nerves and sensory and motor fibers from the pudendal nerve.
URETHRAL ANASTOMOSIS
Preoperative Considerations
• Perform urethral anastomosis for treatment of urethral disruption, prostatectomy, stricture formation, or removal of granulomatous or neoplastic masses.
• Perform a retrograde positive contrast urethrocystography to identify the location of obstruction or disruption.
• Treat animals that are uremic or have other metabolic disorders as a result of urethral obstruction or leakage of urine into the periurethral tissues prior to inducing anesthesia and performing surgery.
Surgical Procedure
Technique
1. The positioning of the animal (dorsal recumbency or ventral recumbency in a perineal stand) depends upon the portion of the urethra to be operated upon.
3. Pass a sterile urethral catheter from the external urethral orifice in a retrograde direction to facilitate identification of the proximal end of the distal portion of the urethra.
4. If the distal end of the proximal portion of the urethra cannot be identified, perform a cystotomy and pass a urethral catheter in an antegrade direction.
5. Excise the damaged portions of the urethra. Although it is critical that a tension-free anastomosis be performed, do not be reluctant to debride and resect an adequate amount of urethra to properly treat the disease process.
6. With the urethral catheter in place, perform the anastomosis by placing full-thickness sutures in a simple interrupted pattern.
9. Gently rotate the urethra to facilitate placement of subsequent sutures. Placing the first two sutures 180 degrees apart facilitates appropriate apposition of the ends of the urethra and suture placement. Preplacement of sutures may help ensure accurate placement of sutures.
10. Place sutures evenly; six to eight sutures are usually sufficient to perform a satisfactory anastomosis.
11. Maintain a soft, preferably balloon-tipped catheter that approximates the diameter of the urethral lumen connected to a sterile urine collection bag for 7 to 10 days after surgery.
12. If necessary, use an Elizabethan collar to prevent catheter displacement. Alternatively, place a cystostomy catheter to divert the flow of urine from the urethra (see Chapter 80).
Postoperative Care and Complications
• If the urethral catheter is removed prematurely, a decision must be made regarding whether or not to replace the catheter. If resistance is encountered during attempts to pass the urethral catheter, replacement is abandoned.
• Warn the owners of the potential for postoperative stricture (most commonly observed 2–3 weeks after surgery), and advise them to carefully observe the animal during urination for evidence of urethral obstruction.
• Perform a retrograde positive contrast urethrocystogram 2 to 3 months after surgery to evaluate the urethral diameter at the anastomotic site.
URETHROTOMY IN THE MALE DOG
Preoperative Considerations
• Perform this procedure to remove urethral calculi lodged proximal to the os penis or in the perineal urethra and to temporarily divert the flow of urine.
• If the animal is azotemic and depressed, this procedure can be performed without sedation by infiltrating the tissue overlying the urethra with local anesthetic.
• If calculi remain in the kidneys, ureters, bladder, or urethra after urethrotomy, perform definitive surgery to remove the calculi after the animal is stabilized.
Surgical Procedure
Technique
1. Restrain the dog in dorsal (prescrotal urethrotomy) or lateral recumbency (perineal urethrotomy). Prescrotal urethrotomy is the preferred technique.
2. If the procedure is not being performed under general anesthesia, infiltrate the skin and subcutaneous tissues overlying the urethra with local anesthetic.
6. In the prescrotal location, identify the retractor penis muscles and retract them laterally. The urethra appears as a purple structure on the midline flanked on either side by the white penile tunic.
8. Pass a urethral catheter from the urethrotomy site into the bladder. Catheterize the distal urethra (retrograde and/or antegrade) to ensure patency.
9. Maintain the urethral catheter after surgery to monitor urine output and diminish the likelihood of subsequent urethral obstruction prior to surgical removal of cystic calculi.
Postoperative Care and Complications
• Hemorrhage may be observed intermittently, usually associated with urination, for 7 to 14 days after surgery. The flow of urine dislodges clots, and urokinase (a plasminogen activator found in urine) interferes with clot formation. This complication may be minimized by suturing the urethrotomy site.
• On rare occasion, a stricture may form at the urethrotomy site. This is more likely when the urethral mucosa has sustained significant damage.
• Treat UTI and calculi with appropriate antibiotic and dietary therapy and other interventions to prevent reformation of calculi. Inform the owner that surgery will not cure this problem and appropriate medical therapy is critical to a satisfactory outcome.
• If calculi from the bladder pass into the urethra, urethral obstruction may recur despite the urethrotomy.
• If the skin incision is made too close to the scrotum, the testes may prolapse through the skin incision. Treat this prolapse by suturing the caudal aspect of the incision.
• Swelling and edema of the scrotum and testes may be observed because of inflammation associated with the urethrotomy or subcutaneous accumulation of urine. Subcutaneous accumulation of urine occurs infrequently if the urethrotomy incision is made near the proximal end of the os penis.
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