Introduction

In general, the goal of surgical management of either traumatic or obstructive disease of the lower urinary tract is to restore normal lower urinary tract structure, thereby restoring normal function. Occasionally, however, this is not possible, and a temporary or permanent salvage procedure must be employed. The goal of such procedures is to restore normal or near normal function by altering or bypassing irreversibly deranged local anatomy. Temporary and permanent urethrostomies are reserved for cats or instances where canine urethral obstructions cannot be relieved by laser lithotripsy, or for patients that have sustained penile/urethral trauma. Tube cystostomy is the most commonly employed temporary urinary diversion technique used in our practice. Urethral stomas are usually made at the scrotal site for dogs (ventral) and cats (perineal) but are occasionally made in a perineal site for dogs and ventral (pre-pubic, mid-pubic and caudal pubic) sites in cats. Finally, stenting of the prostatic urethra can provide palliation for dogs with obstruction associated with prostatic malignancy.

Urethral Obstruction

Diagnosis

Historically, animals affected may have suffered from oliguria, stranguria, and dysuria for hours to days, with little to no urination. Occasionally (more frequently in cats) the animal is presented because of lethargy, weakness and collapse. Physical examination findings reflect the degree of cardiovascular compromise and the presence of a large, very firm bladder on gentle abdominal palpation. Pathophysiological changes seen in these patients include azotaemia, hyperkalaemia, metabolic acidosis, and hypovolaemia.

Initial Evaluation and Stabilization

This will require initial blood tests: PCV, total protein, electrolytes as a minimum. Ideally, full haematology and serum biochemistry and urinalysis should be done. An ECG strip should be obtained or continuous ECG monitoring performed.

Therapy will require intravenous access and should consist of these main elements:

1.  Intravascular fluid volume replacement

2.  Cardioprotection

3.  Correction of electrolyte abnormalities

4.  Relief of the urinary obstruction

A balanced electrolyte solution may be used at initial doses of 10 ml–60 ml/kg/hr depending on the degree of hypovolaemia. 0.9% saline may help correct the electrolyte abnormalities more rapidly. Life-threatening hyperkalaemic bradycardia can be treated by administering calcium gluconate (50–100 mg/kg) to provide cardioprotection while the potassium falls in response to fluid therapy and urine drainage. Insulin or insulin + glucose therapy (to shift potassium into cells) and bicarbonate administration are alternative or adjunctive strategies to aid in the management of hyperkalaemia. Initial stabilization can be aided by cystocentesis, making the patient a better sedation/anaesthetic candidate. The majority of urethral obstructions can be relieved without surgery (see below). Occasionally, obstructions require surgical relief. Once the obstruction is relieved and urine flow is established, the GFR will increase and a post-obstruction diuresis will commence; any metabolic acidosis and electrolyte abnormalities should gradually return to normal over the following 24 hours.

Specific Techniques - Male

Feline

 After judicious use of sedation/anaesthesia, place cat in dorsal recumbency with hind limbs relaxed in a neutral position or held slightly cranially by an assistant.

 Palpate the penile tip. Occasionally, obstructive plugs can be palpated in the tip of the penis and may be "milked" out.

 Extrude the penis, grasp it ventrally at the level of the preputial fornix, and gently pull caudally so as to straighten the urethra.

 Choose a device to catheterise the urethra.

 A 20- to 60-ml syringe of sterile isotonic saline solution should be nearby for retropulsion, preferably with an assistant and an IV extension set attached to it.

 Pass the lubricated catheter as far as it will go without resistance, then continue retropulsion as the syringe is being depressed; immediately discontinue flushing solution once you enter the bladder.

 Some additional retropulsive force may be obtained if distal urethra is pinched around the catheter.

 Remove all urine with the catheter in place, using a syringe (the bladder may be weak or necrotic and may rupture with external manual pressure).

 Lavage bladder with isotonic saline solution until fluid retrieved is relatively clear; further lavage of urethra is indicated unless concerned about being unable to recatheterise urethra.

 Suture and indwelling catheter in place to maintain patency for the immediate short term.

Canine

Principles same as for cat, except:

 Penis is grasped distally (near the tip) and traction is applied cranially (toward the dog's head).

 Urethra is catheterised with appropriate catheter.

 Additional retropulsive force can be generated as follows: assistant occludes pelvic urethra per rectum, distal urethra is distended with isotonic solution as tip of penis is occluded, then assistant releases occlusion in pelvis, creating retropulsive wave.

 Medical dissolution is not often employed in the male canine because of concern that calculi will shrink to size perfect to obstruct urethra; however, others are strongly in favor of medical dissolution of struvite calculi.

Surgical Relief of Urethral Obstruction

Canine Urethrotomy/Urethrostomy

1.  Indications

a.  Urethrotomy is most often employed with obstruction at the base of the os penis, and the urethra is assessed to be fully patent after calculus removal.

i.  Urethrotomy within the os penis frequently results in stricture formation and is not recommended.

ii.  Urethrotomy incisions can be allowed to heal by second intention, healing in 7–10 days; also can be closed primarily with 4-0 or 5-0 synthetic absorbable suture followed by routine skin closure.

iii.  Haemorrhage may be profuse intermittently, especially after urination or at times of excitement.

b.  Permanent urethrostomy is indicated with calculi lodged within the os penis, strictures 2° to previous trauma, or severe acute penile/urethral injury.

2.  Choosing the appropriate location for urethrostomy

a.  Scrotal urethrostomy is the procedure of choice when a permanent urethral opening is desired. Castration/scrotal ablation must accompany this procedure in the intact male.

i.  The membranous urethra in the region of the scrotum is larger and more distensible than at the base of the os penis, allowing the passage of larger calculi and decreasing the risk of stricture formation.

ii.  The scrotal urethra is more superficial and surrounded by less cavernous tissue than the perineal urethra. Hemorrhage is more easily controlled, and surgical exposure is better than with other regions of the urethra.

b.  Pre-scrotal urethrostomy is advocated by some surgeons, "saving" the scrotal urethra in the event the pre-scrotal urethrostomy develops an occlusive stricture.

c.  Perineal and antepubic urethrostomies are indicated if stricture or irreparable laceration/crushing exists proximal to the scrotal urethra.

i.  Perineal urethrostomy may produce persistent urine scald of the perineal epithelium and increased risk of urine extravasation into the periurethral tissues postoperatively.

ii.  Antepubic urethrostomy is technically difficult because vascular and nervous supply to the bladder neck must be preserved.

3.  Approach, surgical manipulation, closure (for scrotal urethrostomy)

a.  Scrotal ablation and castration (for intact males) performed (urethral catheter passed preoperatively if possible).

b.  Retractor penis muscle retracted ± sutured laterally, and corpus spongiosum penis (= corpus cavernosum urethra) and urethra are incised on caudoventral midline, with a desired stoma 1–2 cm long.

c.  Surgery is completed by suturing urethral mucosa to the surrounding skin edge with 3-0 or 4-0 monofilament material (nylon or polypropylene).

d.  Urethrostomy at other sites requires similar manipulations.

4.  Complications

a.  Increased risk of ascending bacterial infection vs. normal anatomy - not borne out by the information currently available.

b.  Cavernous tissues will hemorrhage for up to 10 days postoperatively, especially after urination or sexual stimulation.

c.  Subcutaneous urine extravasation produces profound cellulitis and systemic illness/sepsis: investigate periurethral trauma or cellulitis thoroughly and without delay.

Feline Perineal Urethrostomy

1.  Indications

a.  Obstruction that cannot be relieved with catheterisation (a surgical emergency)

b.  Stricture 2° to distal urethral obstruction
Perineal urethrostomy is performed less frequently now than it was 10–15 years ago, probably as a result of the improved success of treating feline lower urinary tract disease (FLUTD) with aggressive medical therapeutics (antibiotics when indicated, dietary management, careful relief of urethral obstruction) and the recognition of the complications associated with restructuring the male urogenital tract.

2.  Approach, surgical manipulation, closure

a.  Ventral recumbency, in a rectal stand, with a pursestring suture inserted into the anus.

b.  Elliptical incision from just dorsal to the scrotum to ventral to the prepuce; castration is included in this procedure if not already performed

c.  Penis is mobilized with blunt and sharp dissection close to the shaft, and the sharp incision of ventral ligamentous attachments to the ischiatic symphysis and the crus of the penis; the crus may hemorrhage profusely if not subsequently ligated.

d.  Further dissection is employed until penis is freed approx. 1 cm proximal to the paired bulbourethral glands; avoid damage to the rectum, anus, and anal sacs dorsally.

e.  After application of a tourniquet, the penis is amputated just distal to the crura, the urethral lumen is catheterised, and the urethra is incised dorsally to the cranial aspect of the bulbourethral glands.

f.  Simple interrupted sutures of 4-0 nylon (Ethilon), polypropylene (Prolene), or similar are used to appose the full thickness of the urethra to the perineal skin.

g.  Penis is fully amputated once a triangular stoma has been established and the cut ends of the corpus spongiosum are sewn together.

h.  Skin incision is completed with a Penrose drain ventral to the pelvic urethra.

i.  Petroleum jelly is applied to the urethrostomy site twice daily, Elizabethan collar used as needed, and the sutures are removed in 10–14 days under sedation (usually).

3.  Complications

a.  Aggressive periurethral dissection may produce striated-muscle urethral sphincter dysfunction 2° to pudendal nerve damage.

b.  Asymptomatic bacterial cystitis has been reported in about ¼ of the perineal urethrostomies followed long term.

c.  Stricture and/or urethral obstruction secondary to calculi may occur.

Tube Cystostomy

1.  Indications
Temporary urinary diversion following urethral rupture repair or following temporary urethral obstruction. Permanent urinary diversion for palliation of patients with tumoral or traumatic urethral obstruction.

2.  Equipment

a.  Standard coeliotomy instruments and Balfour or Gossett retractors

b.  DePezzer mushroom-tipped or Foley balloon-tipped urologic catheter of appropriate size

3.  Approach
Caudal ventral midline coeliotomy, from umbilicus to pubis

4.  Manipulations
The urinary bladder is examined to ensure that adequate blood supply remains. A location in the ventrolateral bladder wall is identified midway between the trigone and the apex of the bladder. A pursestring suture of 2-0 (3 Ph Eur) or 3-0 (4 Ph Eur) polydioxanone is placed. If a Foley catheter is used, the catheter is placed through a stab incision in the body wall approximately 2 cm lateral to the ventral midline at a level that will minimally distort bladder position before the catheter tip is placed into the bladder. The catheter is then inserted into the bladder lumen through a stab incision in the centre of the pursestring suture. The balloon of the Foley catheter is then inflated but kept away from the bladder wall to avoid inadvertent catheter balloon puncture. Once the catheter tip is inside the bladder, the other end of the catheter should be occluded using artery forceps or similar. If a mushroom-tipped catheter is being used, once it is placed into the bladder the other end must be fed through the body wall in a similar position as previously described for the Foley catheter. Four cystopexy sutures of polydioxanone are preplaced in a box configuration around the abdominal and bladder wall incisions. Ideally, the pexy sutures should pass through the seromuscular layers of the bladder wall and partial thickness through the body wall. The sutures are then tied and the catheter tip is drawn up to the bladder wall. The tube is secured with either a Chinese finger trap suture or tape tabs sutured to the skin. Abdominal closure is routine.

Prepubic, Transpelvic Urethrostomy, and Urethrovaginoplasty

The goal of therapy is to preserve as much of the urethra as possible and create a new urethral stoma either in front of, in the middle of, or caudal to the pubic bone of the pelvis. Occasionally, the urethra can be anastomosed with the vagina to create a continent urinary diversion.

References

1.  Burrow RD, Gregory SP, Giejda AA, White RN. Penile amputation and scrotal urethrostomy in 18 dogs. Vet Rec. 2011;169(25):657.

2.  Liehmann LM, Doyle RS, Powell RM. Transpelvic urethrostomy in a Staffordshire bull terrier: a new technique in the dog. J Small Anim Pract. 2010;51(6):325–329.

3.  Smeak DD. Urethrotomy and urethrostomy in the dog. Clin Tech Small Anim Pract. 2000;15(1):25–34.

4.  Bernarde A, Viguier E. Transpelvic urethrostomy in 11 cats using an ischial ostectomy. Vet Surg. 2004;33(3):246–252.

5.  Baines SJ, Rennie S, White RS. Prepubic urethrostomy: a long-term study in 16 cats. Vet Surg. 2001;30(2):107–113.

6.  Jordan CJ, Kulendra E, Perry KL, Halfacree ZJ. Management of peristomal tissue necrosis following prepubic urethrostomy in a cat. Vet Comp Orthop Traumatol. 2012:25(5).