Surgical Revision of the Urethral Stoma Following Perineal Urethrostomy in 11 Cats: (1998–2004)

Introduction

Urethral obstruction is a possible complication of feline urologic syndrome, a condition in which urethral crystals, stones, mucous plug formation, inflammation, and hematuria contribute to a mechanical obstruction of the distal urethra, particularly in male cats.¹ Perineal urethrostomy was first reported in 1963 as a treatment for distal urethral obstruction and trauma in male cats. This report described transecting the urethra cranial to the penile portion, exteriorizing the wider pelvic urethra, and suturing it to the perineal skin.² Numerous modifications of the technique have been reported.^2–6 Currently, the most commonly used technique is that reported by Wilson and Harrison.³

Although perineal urethrostomy is usually a successful procedure when performed correctly, numerous serious complications have been reported, including stricture formation and recurrent obstruction, bacterial urinary tract infection, sterile cystitis, urine extravasation at the surgical site, urinary and fecal incontinence, rectal prolapse, rectourethral fistula formation, and perineal hernia.^7–12 Less serious, transient complications are relatively common and may include dysuria, pollakiuria, hematuria, hemorrhage, and skin fold dermatitis at the surgical site.^8,12,13 Although stricture of the surgical site is a reported complication of perineal urethrostomy, no study has evaluated perineal urethrostomy stricture development beyond 12 weeks postoperatively or the long-term results of surgical stricture revision.^{7,8,11,12,14,15}

The purpose of the study reported here is to describe the history, presenting complaints and clinical signs, the pathophysiology, and the prognosis for those cats that developed urethral stricture following perineal urethrostomy. The gross appearance of the surgical site at the time of stoma revision and the long-term clinical outcome following revision are also reviewed.

Materials and Methods

Medical records from the Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania (MJR-VHUP) were retrieved for cats that underwent revision of perineal urethrostomy from 1998 to 2004. Male cats were included in the study if they had a previous perineal urethrostomy, were presented for urethral obstruction after surgery, and had a revision of the perineal urethrostomy site performed at MJR-VHUP. Data retrieved from the records included signalment (i.e., age, breed, gender, body weight); postoperative complications following initial perineal urethrostomy; time between initial perineal urethrostomy and revision of the urethral stoma; presenting complaints, clinical signs, and physical examination findings prior to the second perineal urethrostomy procedure; hematological abnormalities and urinalysis findings on presentation for perineal urethrostomy revision; diagnostic imaging studies performed prior to stoma revision; and the gross appearance of the urethra and surrounding tissues at the time of stoma revision. Stricture following perineal urethrostomy was defined as a stoma so small as to create a functional or mechanical urethral obstruction that prevented normal urination or expression of the urinary bladder.

Revisions of the perineal urethrostomy stoma sites were performed using the technique described by Kusba and Lipowitz.¹⁴ Using this technique, a circumferential incision is made around the stoma. The ischiocavernosus muscles or their remnants are dissected free from their attachments. The penis is then elevated dorsally, and ventral attachments are also freed. A dorsal midline incision is made into the urethra along the penile remnant to the cranial extent of the bulbourethral glands, and the urethral mucosa is sutured in gentle apposition with the perineal skin. The penile and urethral remnants are then transected at the original strictured mucocutaneous junction, and the mucosa-to-skin sutures are continued ventrally to create the drain board of the urethral stoma. The remaining skin is sutured together using monofilament, nonabsorbable suture material [Figure 1].¹⁴ Follow-up information for each case was obtained via a standardized phone interview with each owner.

Results

Eleven cats satisfied the inclusion criteria for the study. All 11 were castrated male, domestic shorthair cats. The median age at presentation for stoma revision was 4.8 years (range 1.3 to 12.2 years). Median weight at presentation was 5.5 kg (range 4.1 to 8.0 kg).

All initial perineal urethrostomy surgeries were performed by the primary care veterinarians. The initial surgical techniques utilized were unknown. Hyperemia of the surgical site was noted immediately after surgery in eight cats. Marked edema and bruising of the perineal area and hind legs were seen in three of these eight cats. One of these three cats was presented to MJR-VHUP for stoma site revision 4 days following initial perineal urethrostomy. Two of the three cats were presented to the primary care veterinarians 5 and 7 days following initial perineal urethrostomy. Signs of dysuria, hind-limb and perineal edema, and bruising were managed conservatively until presentation to MJR-VHUP 34 and 66 days, respectively, following the initial procedure. For all cats, the median time between the initial perineal urethrostomy procedure and stoma site revision procedure was 71 days (range 4 to 1623 days). Six (55%) cats presented for stoma site revision ≥ 10 weeks following the initial perineal urethrostomy.

Presenting complaints prompting surgical evaluation of the stoma site included stranguria (n=5), dribbling of urine (n=3), vocalization on urination (n=3), inappropriate urination (n=3), hematuria (n=1), dyschezia (n=1), bruising of the perineum (n=1), and licking at the urethral stoma (n=1). Other clinical signs included vomiting (n=2) and weight loss (n=1). The urethral stoma (from the initial perineal urethrostomy) was visibly narrowed in eight cats [Figure 2]. No reference was made to urethral stoma size in the records of three cats. These three cats developed marked hyperemia, edema, and bruising of the perineal area and hind legs, and these signs were considered indicative of urine extravasation into the subcutaneous tissues. These three cats were presented for stoma revision a median of 34 days (4, 34, and 66 days) following initial perineal urethrostomy, while the other eight cats were presented a median of 170.5 days postoperatively (range 52 to 1623 days).

Routine hematological analyses via an amperometric autoanalyzer,^a complete blood counts, and biochemical profiles revealed elevations in lactate (n=3, range 2.7 to 3.5 mmol/L, reference range 0.6 to 2.5 mmol/L), aspartate aminotransferase levels (n=6, range 49 to 93 U/L, reference range 1 to 37 U/L), leukocytosis (n=3, range 12,900 to 14,000 cells/μL, reference range 2500 to 12,500 cells/μL), and anemia (n=3, hematocrit range 23% to 28%, reference range 31.7% to 48%). A urinalysis was performed in 10 cats, and urine pH varied from 6.0 to 8.0 (median 6.5). Ten cats exhibited an active urine sediment with varying degrees of pyuria and hematuria, and four cats had bacteruria.

Preoperative imaging studies were performed in three cats. A positive-contrast retrograde urethrocystogram was performed in one cat and revealed a distal urethral stricture with evidence of prestenotic urethral dilatation. In one cat, abdominal radiographs revealed the presence of a 3 mm-diameter calculus in the distal urethra. In another cat, abdominal ultrasonography showed evidence of grit in the bladder lumen.

The gross appearance of the urethra and surrounding tissues at the time of perineal urethrostomy revision surgery was noted in each case. Eight cats had an intact penile urethra, with clear evidence of inadequate dissection to the level of the bulbourethral glands [Figure 3]. Three cats with hind-limb edema and bruising from presumed subcutaneous urine leakage had urethral strictures, granulation tissue around the stoma, and subcutaneous edema and erythema consistent with cellulitis [Figure 4].

Long-term follow-up after stoma revision was obtained in nine of the 11 cases. The median follow-up time was 2.2 years (range 1.4 to 6.1 years). In eight of nine cases, owners reported the cats did well after the revision surgery, with no complications. One cat urinated out of the litter box intermittently and occasionally licked at the stoma site. This behavior commenced in the early postoperative period, despite timely suture removal at 11 days after surgery. The behavior in this cat persisted with the same frequency for 2 years following stoma revision, and no other signs of urethral obstruction were noted on physical examination by the referring veterinarian.

Discussion

Perineal urethrostomy is a surgical option for urethral obstruction in male cats, especially those with life-threatening signs from their urethral obstruction, repeated episodes of urethral obstruction, and those not responsive to conservative, medical management.^3,4,16 Other possible indications include irreversible distal urethral trauma and neoplasia of the penile urethra.^17,18

Perineal urethrostomy is not without potential complications. Life-threatening complications include urine extravasation into surrounding perineal tissues, urinary and fecal incontinence, rectal prolapse, perineal hernia, and urethral stricture.^7–12,19 The distal urethra of the male cat is prone to obstruction and stricture in part because of its anatomy. The urethra is anatomically subdivided into four sections—namely the preprostatic, prostatic, and postprostatic, which comprise the pelvic urethra and the penile urethra. The penile urethra is the narrowest of the four sections, with an average internal diameter of approximately 0.7 mm.²⁰ The average internal diameter of the urethra at the level of the bulbourethral glands is 1.3 mm—nearly twice that of the penile urethra.²⁰ The internal diameter of the preprostatic urethra averages 2.0 mm, and the postprostatic urethra averages 2.3 mm in diameter—over three times that of the penile urethra.²⁰ For this reason, it is imperative that urethral dissection during perineal urethrostomy continues to the cranial extent of the bulbourethral glands.^3,21 Failure to dissect to this level results in marsupialization of a portion of the urethra that has a small internal diameter and creation of a stoma that is prone to stricture after healing.⁷

The findings in this small number of cats with perineal urethrostomy strictures emphasized the importance of a thorough understanding of the surgical anatomy and a need for meticulous surgical technique when performing the procedure. In the cats reported here, urethral stricture was associated with improper technique at the time of the first surgery. In eight of 11 cats, the dissection did not involve the urethra to the level of the bulbourethral glands. Suturing of the narrow penile urethra to the skin presumably resulted in an inadequate stoma that subsequently strictured. Proper wound closure results in primary healing by apposition of viable tissues without tension. Primary healing of mucosa to skin occurs via the intercurrent processes of coagulation, inflammation, angiogenesis, fibroplasia, and minimal epithelialization and contraction.^22,23 In properly sutured wounds under minimal tension, the epidermal cells at the cut edge thicken, and basal cells of the skin margins become mobile and migrate across the wound gap. These epidermal cells bridge the gap generally within 48 hours.²² Finally, a rapid contact inhibition of cells from apposed wound edges minimizes wound contraction and scarring.²⁴ However, inadequate urethral mobilization in feline perineal urethrostomy creates excessive tension at the healing stoma site. Excessive anastomotic tension results in ischemia, inflammation, separation of urethral margins, and increased formation of granulation tissue that contains contractile myofibroblasts.²⁵ In addition, inadequate dissection of the penile urethra creates a stoma from a portion of the urethra with a small diameter. Excessive wound tension may result in wound contraction and stricture formation at the site of an initially small stoma.

In three of 11 cats, adequate mucosa-to-skin apposition was likely not obtained, as evidenced by immediate postoperative development of hind-limb and perineal edema and bruising, which were consistent with leakage of urine into the subcutaneous space. Mucosa-to-skin apposition is critical to the development and maintenance of an adequate stoma and drainboard for the passage of urine. Adequate mucosa-to-skin apposition is assured by pre-placement of sutures that bring the most cranial aspect of the incised urethral mucosa into gentle apposition with the tissue of the dorsal aspect of the skin incision.³ In addition, the urethral mucosa should be carefully identified by its white, glistening, striated appearance. Failure to bring the mucosa and skin into adequate apposition may result in leakage of urine into the subcutaneous spaces surrounding the urethrostomy site, the perineum, and hind legs. Urine is hyperosmolar and irritating to the surrounding tissues and causes profound inflammation in these subcutaneous areas.²⁶ Fluid collection between the surrounding subcutaneous tissues further interferes with apposition and delays healing by interfering with the blood supply to the area.^27–29 When mucosa-to-skin apposition is inadequate, second-intention healing involving fibroplasia, marked contraction, and epithelialization attempts to bridge the larger wound gap.²⁷ Wound contracture refers to the pathological effects of contraction and excessive scar tissue formation, which may lead to stricture of the urethral stoma and subsequent urethral blockage.³⁰ Other possible causes of urine extravasation into the subcutaneous space include traumatic catheterization, resulting in urethral mucosal injury, and inadvertent laceration of the urethra during dissection for perineal urethrostomy; however, no evidence of iatrogenic urethral trauma was found at the time of stoma revision in any of these three cats.⁷

Of interest was the broad range of time over which urethral strictures developed in these cats (i.e., 4 to 1623 days following initial perineal urethrostomy). Previous reports of urethral stricture following perineal urethrostomy described the need for stoma site revision from 9 to 84 days postoperatively.^7,14 Another report described complications following perineal urethrostomies in 103 cats.¹⁵ One of these cats was diagnosed with urethral obstruction 1 year after initial perineal urethrostomy, and scar tissue was excised from the stoma site at that time. However, no conclusions could be drawn regarding the pathogenesis of postoperative urethral obstruction in this cat, because no information was provided on the following: initial postoperative complications; clinical signs at presentation for scar excision; hematological, urinalysis, or radiographic abnormalities; the gross appearance of the urethra and surrounding tissues at the time of the second procedure; and the type of surgical procedure performed.¹⁵ It is unclear why a greater proportion of cats in the study reported here were presented for stoma revision much later after initial perineal urethrostomy than were the cats described in previous studies.^7,14 In the study reported by Smith and Schiller, perineal urethrostomies were performed using one of four techniques (i.e., those described by Wilson, Blake, Carbone, and Christensen).⁷ Strictures developed most commonly following preputial urethrostomy, as described by Christensen. The authors of the study concluded that inexperience with the technique and the early postoperative use of urinary catheters may have led to stricture formation.⁷ In the study reported by Kusba and Lipowitz, the initial surgical techniques performed were unknown, but all six cats had intact ischiocavernosus muscles and inadequate dissection of the penile urethra at the time of revision surgery.¹⁴ It is also possible that cats in previous studies suffered undetected, early postoperative complications (such as urine leakage into the subcutaneous space) that caused more rapid development of the urethral stricture. Other reported causes of strictures (e.g., calculi or catheter-induced urethritis, remodeling of scar tissue in the periurethral tissues, traumatic surgical technique, wound infection or recurrent urinary tract infection, neoplasia) may also have affected the timing of stricture formation in earlier reports.³¹

Limitations of the current study included low case numbers, its retrospective nature that allowed for an inherent bias in case selection, incomplete follow-up on some cats, and the subjective nature of assessments made at the time of revision surgery. However, assessments of the adequacy of the original urethrostomy dissection and accuracy of apposition of tissues were made objectively and indicated that poor surgical technique predisposed to postoperative stricture formation in the cases presented here.

Conclusion

Eleven cats required revision of their urethral stomas because of stricture following perineal urethrostomies. Failure to dissect beyond the level of the bulbourethral glands and inaccurate apposition of urethral mucosa to perineal skin likely resulted in the postoperative strictures reported here. Stricture formation occurred later after surgery than was previously reported. Based on these findings, careful attention should be given to the level of urethral dissection and the meticulous apposition of urethral mucosa to perineal skin when performing a perineal urethrostomy.

Acknowledgment

The authors thank Dorothy Cimino Brown, DVM, Diplomate ACVS, for her assistance in preparing this manuscript.