Author

Stephen J. Birchard DVM, MS, Diplomate ACVS

Tuesday, September 23, 2014

Urethral Prolapse in Dogs: Why it happens and how to fix it.


Prolapse of the urethral mucosa is a rare condition that occurs in male dogs.  Young, intact, brachycephalic dogs, such as bulldogs or Boston terriers, are commonly affected.  The cause of the prolapse in most cases is unknown, but may be related to excessive sexual excitement or underlying urogenital disorders such as urethritis or urethral calculi.  Some authors believe that the relationship between brachycephalic breeds and urethral prolapse may be due to abnormal urethral development or increased abdominal pressure secondary to upper airway obstruction that is typical for these breeds.(1)  Increased abdominal pressure could impair venous return and subsequently cause chronic engorgement of the corpus spongiosum tissue surrounding the distal urethra. (1)

Clinical signs
Clinical signs of prolapsed urethra are bleeding from the prepuce, discomfort, and in rare cases, stranguria.  Affected dogs may show excessive licking of the penis.  Examination of the penis by extruding it from the prepuce reveals the protruding mucosa as a characteristic round, donut-shaped mass at the tip of the penis. (Fig. 1a)
Fig. 1a: urethral prolapse in a dog (arrow)
The prolapsed mucosa is bright red to dark purple.  A urethral catheter usually can be passed through the center of the tissue.  Differential diagnosis would include neoplasia such as transmissable venereal tumor, or penile trauma.

Diagnosis
Dogs with urethral prolapse should be thoroughly examined and evaluated for underlying urogenital disease or other disorders. Perform rectal examination to evaluate the pelvic urethra for a mass or calculus. Catheterize the urethra to determine urethral patency and other possible problems such as calculi.  Obtain urine for analysis and culture to rule out bacterial infection of the urinary tract.  Plain film abdominal radiographs and abdominal ultrasonography should be obtained to evaluate the kidneys, urinary bladder, and prostate gland. Positive contrast studies of the urinary tract can be done if indicated.
When urethral prolapse affects in tact male dogs castration should be recommended to decrease sexual excitement, a possible factor in the pathophysiology of urethral prolapse.  Although medical management of urethral prolapse has been described, surgical treatment by either mucosal resection or urethropexy offers the most expeditious option to alleviate clinical signs and prevent recurrence.

Surgical Technique
The animal is anesthetized and placed in dorsal recumbency.  The prepuce and surrrounding area are clipped and aseptically prepared.  The penis and interior of the prepuce are also gently scrubbed and irrigated with antiseptic solution.  After prepping the prepuce for aseptic surgery, the surgical site is draped and the penis extruded using   assistant’s fingers or by placing a Penrose around the caudal aspect of the penis to hold the prepuce caudally. (Fig 1a,b)
Fig. 1b: surgical model of a penis and urethral prolapse
            Urethral mucosal resection
A lubricated, sterile urinary catheter is passed into the urethra.  A 180o incision is made at the base of the prolapsed mucosa, as close to the penile tunic as possible. (Fig 2a,b)
Fig. 2a: incision in urethral mucosa with a scalpel blade
Fig. 2b incising urethral mucosa
The incision can be started with a scalpel (#15 blade), and continued with Metzenbaum or tenotomy scissors. (Fig. 3)
Fig. 3: continuing incision in urethral mucosa with scissors
The mucosa is not initially completely excised all the way around the urethral lumen since this will result in retraction of the mucosa and difficulty in suturing. The incised mucosa is then sutured to the penile tunic with 4-0 or 5-0 Monocryl or PDS in a simple continuous pattern with a small taper needle. (Fig. 4)
Fig. 4: suturing normal mucosa to penile tunic, simple continuous pattern. Note
inside out direction of needle placement (arrow)
Sutures are placed about 2-3 mm apart and the suture bites are made from inside the urethral lumen to the outside.  A recent study found that the simple continuous suture pattern resulted in a decreased incidence of recurrence of urethral prolapse.(2)
Fig. 5: half of the mucosa has been sutured and the pattern ended
Handle the healthy mucosa gently and avoid excessive manipulation with thumb forceps.  After the initial sutures are placed, the remainder of the prolapsed mucosa is resected and then sutured. (Fig. 6) 
Fig. 6: the remainder of the prolapse mucosa is resected and sutured.
Submit the excised tissue for histopathology to definitively rule out neoplasia.

            Urethropexy
An alternative to mucosal resection is urethropexy (3). In this technique, after prepping the site as described above, the prolapsed mucosa is pushed to the inside of the penis using a red rubber catheter. This catheter is modified by removing a portion of the tip lengthwise.  Sutures (4-0 PDS) are placed starting at the outer surface of the penis, then guiding it to the groove in the catheter and then exiting through the mucosa and to the urethral lumen. The suture needle is then redirected to enter the urethral lumen, again within the groove of the catheter, and exits the penis adjacent to the original entry point (mattress pattern). Three or four of these sutures are placed to secure the mucosa to the urethral lumen. 

Postoperative Care
Remove the urinary catheter after the procedure.  Place an Elizabethan collar on the dog to prevent licking of the surgical site.  Intermittent bleeding from the penis may persist postoperatively for a few days.  Tranquilization with acepromazine (0.05 mg/kg subcutaneous or IM, not exceeding a total dose of 3 mg) often is beneficial in reducing bleeding.  Excercise is limited for 7-10 days to leash walking only.  Treatment of underlying urinary problems, such as cystitis or prostatitis, should also be treated appropriately. The absorbable sutures do not need to be removed.

The prognosis for these animals is usually good although recurrence is common; 57% of dogs recurred in one recent study. (2) The treatment of recurrence is to repeat the surgical treatment as described above. Continue to be diligent in looking for an underlying etiology.  Penile amputation combined with scrotal urethrostomy may be necessary in the rare case that does not respond to repeated resection of the prolapsed tissue.

 References

1. Osborne CA, Sanderson SL. Medical management of urethral prolapse in male dogs. In Bonagura and Kirk, eds. Kirk’s Current Veterinary Therapy XII, Philadelphia: WB Saunders, 1995:1027-1029.

       2. Urethral Prolapse in Dogs: A Retrospective Study. Jennifer G. Carr1, DVM, Karen M. Tobias, DVM, MS, Diplomate ACVS, and Laura Smith3, BVMS. Veterinary Surgery 43 (2014) 574–580.

      3. Kirsch JA, Hauptman JG, Walshaw R. A urethropexy technique for surgical treatment of urethral prolapse in the male dog. Journal of the American Animal Hospital Association [2002, 38(4):381-384]