Urethra (Proceedings)

Article

The entire urethra is lined with transitional epithelium with the exception of a small amount near the tip of the penis or urethral tubercle.

Anatomy

The entire urethra is lined with transitional epithelium with the exception of a small amount near the tip of the penis or urethral tubercle. Urethral muscle is composed of an inner longitudinal layer of smooth muscle and an outer transverse layer of skeletal muscle that are separated dorsally by a longitudinal raphe.

Blood supplies are mainly from the urogenital and/or internal pudendal arteries depending on whether the dog is a male or female. Venous drainage is primarily through the internal pudendal vein. Autonomic nerves from the pelvic plexus supply the smooth muscle of the urethra. Voluntary control of muscle is mediated by the pudendal nerve.

Pathophysiology

Urethral reaction to foreign objects is dependent on many variables; e.g., individual patient response, length of time the foreign objects are lodged, the type of foreign object (calculi, catheter, etc.), and absence or presence of secondary infection. In humans, urethras show some reaction after 2-3 days of indwelling catheter. This reaction is superficial and does not clearly indicate that the degree of submucosal reaction is probably important in breaking down body defense mechanisms to infections as well as in causing scarring of the urethra after the foreign body has been removed.

Surgery of the urethra

Urethral prolapse - the cranial prepuce and surrounding abdomen are clipped and scrubbed. The preputial diverticulum and penis are irrigated with an antiseptic solution prior to scrubbing and draping. When the prolapse is small and not grossly engorged with blood, a conservative repair is indicated. The penis is extended from the sheath and grasped between the thumb and forefingers. A well lubricated catheter of the largest diameter that can easily be inserted is passed up the urethra as an attempt is made to reduce the prolapse. If the prolapse easily reduces, the catheter is inserted a short distance into the urethra and a purse-string suture of 3-0 or 4-0 nylon material is placed around the end of the penis The catheter is sutured to the prepuce to maintain its position in the urethra and bladder for 5-7 days. When the prolapse is severe, amputation of the prolapsed segment is preferred. Again, a well-lubricated catheter is placed in the urethra. To prevent the inner mucosa from retracting, four stay sutures are placed equidistant around the tip of the penis and through the urethral mucosa. The prolapse is excised over the catheter as close to the tip of the penis as possible. Simple interrupted sutures of 4-0 or 5-0 PDS are paced around the tip of the penis approximately 0.25 to 0.5 cm apart, uniting the urethral mucosa to the cranial tip of the penis. The catheter is sutured to the prepuce to maintain its position for 3-4 days.

Post-operative considerations - a urinary antibiotic e.g. chloramphenicol or nitrofurantoin is indicated for treatment of any infection. Antispasmodics and/or tranquilizers may be beneficial. Elizabethan collars are useful in preventing catheter removal and licking at the operative site.

Urethrostomies - creation of a new and permanent urethral orifice are performed as one of three types in the male dog, prepubic, scrotal, and perineal. The perineal region is by far the least desirable because of urine scalding of the perineal skin and scrotum. It is also more difficult to suture deep urethra to the skin, if castration is acceptable, scrotal urethrostomy is preferred. If castration cannot be performed, a prepubic urethrostomy is the alternative. The indications for this are recurrent stone formation untreatable or unresponsive to medical management, urethral strictures, and patients where medical management might be harmful.

Prepubic urethrostomy - the caudal ventral abdomen and prepuce are clipped, scrubbed and prepared for surgery. A well lubricated urethral catheter is inserted into the penis to the point of obstruction. A 2-3 cm ventral midline incision is wade in the prepuce over the obstructed site, just caudal to the Os penis, and 1-2 cm cranial to the cranial margin of the scrotum. The penis is grasped between the surgeon's thumb and forefingers to facilitate dissection to the urethra. The subcutaneous tissue is sharply incised to the retractor penis muscle as near the midline as possible. The retractor penis muscle is identified, isolated, and retracted laterally. At this point the ventral portion of the urethra is visible, surrounded completely by corpus cavernous urethra. An incision is made into the ventral urethral lumen over the calculi or catheter and extended 1-1.5 cm in length. The calculi are removed or retrograded into the bladder as the catheter is advanced. After urethral irrigation, the urethral mucosa is sutured in a simple interrupted pattern through the edge of the incised urethral mucosa, corpus cavernous urethra and skin. The urethrostomy opening should be approximately 1.5-2 cm long. One suture should be at the caudal aspect of the incision to create a rounded opening, this will help prevent the skin from growing over the urethrostomy opening.

Scrotal urethrostomy - this surgery relieves strictures of the urethra and allows calculi to pass out and not lodge at the Os penis. The scrotum and surrounding area are clipped, scrubbed and draped. An elliptical skin incision is made around the circumference of the scrotum at its base. The scrotal skin is removed and a routine castration performed. The retractor penis muscle is exposed and dissected from the corpus spongiosum penis and retracted laterally. The ventral portion of the urethra is exposed and appears as a white glistening band of tissue between two bands of cavernus tissue. The urethra is incised for 3-4 cm from its ventral-most portion to the dorsal curve (around the ischial arch). Two stay sutures are placed in the lateral urethral edges. Suturing should begin with the caudal urethral incision to insure an adequate round opening of the urethra. 4 Corner sutures at 45 degree angles are placed. The lateral skin edges are sutured to the urethra with (4-0 or 5-0) PDS suture material in a simple interrupted pattern. Undue tension on the sutures should be avoided and a cosmetic closure obtained.

Postoperative care – (following calculi analysis) culture and sensitivity, prolonged therapy as described above should be instituted.

Perineal urethrostomy - not advocated in the dog due to possible post-operative complications; i.e. urine burns of the skin. A urethral catheter is inserted into the urethra as far as possible; the patient is placed in a perineal position with the tail secured over the back. The perineal area is clipped, scrubbed, and draped after a purse string suture is placed in the anus. A skin incision is made on the midline approximately 2-3 cm dorsal to the scrotum.

The subcutaneous tissue over the urethra, which lies deep on a midline surrounded by the bulbo cavernous muscle, is incised. The urethra can be identified by palpation of the previously incised urethral catheter. The urethra and surrounding cavernous tissue are moved to the incision by gentle manipulation and help with Allis forceps or stay sutures. The fibers of the bulbo cavernous muscle are separated longitudinally over the urethra and the urethra incised over the catheter. Sutures of simple interrupted 4-0 PDS are placed in the urethral mucosa and skin edges to create the urethrostomy opening.

Post-operative considerations - if calculi are flushed into the bladder) a cystotomy is indicated. An Elizabethan collar should be placed on the animal for at least three days. Urinary antibiotics are administered for 30 days post-operative if the procedure is improperly performed, urine may extravate into surrounding tissue and create severe edema and inflammation. Hemorrhage up to 10 days post-surgery is common.

Obstruction of the distal urinary tract in male cats is common. Stabilization of the patient with restoration of normal renal function should be attempted before surgical intervention. Should renal function be severely compromised due to prolonged obstruction, prognosis is guarded at best.

Perineal Urethrostomies in the cat - the hair of the perineum and external genitalia is clipped and the area scrubbed. A purse-string suture is placed in the anus to eliminate fecal contamination of the surgical field. The patient is placed in the ventral recumbent position with the perineum elevated approximately 30 degrees. The tail is extended over the dorsal midline and immobilized. An open-ended tom cat catheter is positioned. An elliptical incision is made to incorporate the scrotum and prepuce. The prepuce and scrotum are removed, exposing the testes in the intact male or fat in the castrated male. If the cat has not been castrated, castration is performed at this time. The penis is dissected from the surrounding tissue to its pelvic attachment on the ischium. It is reflected dorsally and the ventral dissection is begun. The attachments of ischio-cavernosis is severed, thus freeing the crus of the penis. As the dissection continues, the scissors should be kept parallel to the pelvic floor to avoid lacerating the pelvic urethra. With the penis in dorsal reflection, the ligament of the penis is incised. After this procedure, the penis and pelvic urethra can be freed from the pelvic floor by blunt dissection. The penis is reflected ventrally and the loose areolar tissue on the dorsal aspect of the penis is excised to expose the retractor penis muscles, which lie dorsal to the penile urethra. The bulbocavernosis muscle and bulbourethral glands will also be exposed at the distal pelvic urethra. In the castrated male the bulbourethral glands are atrophied, while in the intact male these glands may be quite large. The retractor penis muscle should be carefully removed from the dorsal aspect of the penis over the penile urethra and blunt finger dissection will help to free the pelvic urethra. The penile urethra is incised longitudinally through the glands penis to the pelvic urethra. This should be done carefully with a scalpel over the indwelling catheter. The incision must extend 1 cm into the pelvic urethra (cranial to the bulbourethral glands) which has a larger diameter than the penile urethra. The pelvic and penile urethra mucosa are sutured to the perineal skin with 4-0 PDS. The distal penis is amputated and the remaining penile urethral mucosa is sutured to the skin. The bladder should be expressed to demonstrate patency of the urethrostomy opening and flushed to clear debris that may be present.

Post-operative considerations - remove the purse string suture from the anus; remove sutures in 7-10 days. Do not use litter but rather shredded paper towel or Yesterday's News cat litter so debris does not stick to the surgical incision. Place an Elizabethan collar on the cat.

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