Management of peristomal tissue necrosis following prepubic urethrostomy in a cat

Summary This report describes the successful management of peristomal tissue necrosis following prepubic urethrostomy in a cat. The novel technique of temporary urethral ligation was used in combination with temporary tube cystostomy and vacuum assisted closure to allow for wound management prior to performing wound closure by utilization of a flank fold skin flap then definitive prepubic urethrostomy. Eleven month follow-up indicated excellent outcome with the cat having returned to normal behaviour apart from having adapted its posture to urinate.


Introduction
Prepubic urethrostomy (PPU) is a salvage procedure for the permanent bypass of urethral lesions of the membranous and penile urethra (1). Complications include On presentation the cat was obtunded. Tachycardia with extensive caudoventral abdominal and perineal inflammation were evident. Abdominal ultrasonography did not reveal any free abdominal fluid. Initial packed cell volume was 29% and total solids were 72 g/l. An emergency blood gas and biochemical panel revealed an elevated creatinine of 552.0 (reference interval [RI] 50.0 -140.0) μmol/L and an elevated urea that was too high to measure (RI 3.0 -10.0, maximum readable concentration 35.7 mmol/L). Urinary catheterisation under sedation was unsuccessful so decompressive cystocentesis was performed yielding 135 ml of urine. Refractometric urine specific gravity was 1.039. Following decompressive cystocentesis and intravenous fluid therapy at 4 ml/kg/hr with compound sodium lactate creatinine reduced to 206.0 (RI 50.0 -140.0) μmol/L but blood urea levels remained too high to measure.

Surgical management
The day following admission, the cat's condition had stabilised and it was anaesthetised for further investigations and surgical management. Methadone a (0.2 mg/kg) pre-medication was administered. Anaesthesia was induced with 0.3 mg/kg midazolam b and alfaxalone c to effect and maintained with isoflurane d in oxygen e . Intra-urinary incontinence, peristomal skin irritation, and tissue necrosis (1,2). In one study, six of 16 cats in which a PPU was performed developed some degree of urinary incontinence (2). Two of these cats were refractory to therapy and were euthanatized (2). In the same study, stoma complications were seen in seven cats, four of which were euthanatized (2). In another study of 37 cases of PPU in cats, one cat died from peristomal urine leakage, two cats were euthanatized due to stricture of the PPU stoma, one for recurrent cystitis, and one for urinary incontinence (1). Peristomal tissue necrosis has a reported incidence rate of 12.5 -25.0% and has been reported to occur from between three days to 84 months postoperatively (1,2).
To the authors' knowledge, successful management of peristomal tissue necrosis following prepubic urethrostomy has not previously been described in the cat. In this report, we used vacuum assisted closure (VAC) and the novel technique of tube cystostomy with temporary urethral ligation followed by urethrostomy via a flank skin fold advancement flap to enable the successful treatment of peristomal tissue necrosis following a pre-pubic urethrostomy in a cat.

Case history
A seven-year-old male neutered Domestic Shorthaired cat was referred for evaluation and management of urethral rupture following a suspected road traffic accident the previous day. Contrast retrograde urethrography performed by the referring veterinarian had revealed intrapelvic extravasation of contrast medium at the level of the proximal membranous urethra. Eleven days following surgery (day 12), a bacteriology swab was taken of the wound as it appeared inflamed. Fourteen days postoperatively (day 15), skin necrosis was observed again (ǠFig. 2). A mini-laparotomy was performed under routine general anaesthesia and a 16 French cystostomy tube k was placed, exiting from the left lateral abdominal wall. The necrotic peristomal tissue was debrided and the urethra was temporarily ligated at its most distal extremity with 2 metric polypropylene l . Stay sutures were placed through the distal aspect of the urethral remnant using 2 metric polypropylene to aid identification postoperatively. The urethral remnant was placed within a Penrose drain m to prevent unwanted adhesions forming. The surgical wound superficial to the abdominal wall was left open, thoroughly lavaged with warm sterile saline, and covered with a large non-adhesive dressing n . A 4 French 6 cm jugular catheter o was also placed. Dressing changes were performed every 24 -48 hours.
Seventeen days postoperatively (day 18) vancomycin resistant Enterococcus faecalis was isolated from the bacteriological culture taken 11 days postoperatively, thus prompting antibacterial therapy to be altered consistent with sensitivity results.
Nineteen days postoperatively (day 20), wound debridement and lavage was performed under general anaesthesia leaving a healthy tissue bed (ǠFig. 3). Due to the extent of the ventral abdominal wound, a vacuum assisted closure (VAC) dressing was placed. Sterile, open-cell polyurethane foam p was roughly contoured and placed within the wound and a recess fashioned to accept the urethral remnant contained within the Penrose drain. A translucent, thin, occlusive, adhesive film dressing p was placed over the wound. The central portion of the dressing was perforated and a second translucent, thin, occlusive, adhesive film dressing with integrated suction tubing p was placed over the perforation. The suction tubing was then connected to a continuous suction pump with a collection canister p . The above described foam, dressings and continuous suction pump were supplied as a negative pressure wound therapy package p . All leaks were sealed until a continuous pressure of 125 mmHg below atmospheric pressure was achieved. This procedure was repeated under general anaesthesia every 48 -72 hours or as required.
Twenty-eight days following the initial surgery (Day 29) tertiary closure of the wound was performed under general anaesthesia. The wound was lavaged with sterile saline and the Penrose drain around pelvic extravasation of contrast f was identified originating from the proximal membranous urethra. Cefuroxime g (20 mg/kg) was administered intravenously perioperatively, continued at two-hour intervals throughout surgery, and subsequently continued every six hours for 48 hours postoperatively. A ventral midline coeliotomy was performed and the proximal urethra was identified and debrided. A routine prepubic urethrostomy was performed (1). Oral cephalexin h (15 mg/kg, twice daily) was continued postoperatively.
Seven days postoperatively (day 9), peristomal tissue necrosis developed and rapidly progressed. Peristomal extravasation was confirmed by retrograde contrast urethrocystography under general anaesthesia (ǠFig. 1). Following standard preparation, a large amount of urine was drained from the subcutaneous tissue using suction. Sterile saline i was instilled into the urinary bladder and when expressed, the saline was identified to be leaking from the cranial aspect of the urethrostomy site. The surgical wound at the cranial aspect of the urethrostomy site was reopened, debrided and lavaged with sterile saline then re-sutured. A closed suction drain j was placed in the subcutaneous dead space. Day nine, seven days post prepubic urethrostomy. Positive contrast retrograde urethrocystography. Positive contrast can be seen extravasating from the urethra into the subcutaneous tissues external to the body wall. Fig. 2  A flank skin fold advancement flap was elevated from the right flank region and the wound was omentalised (3). The elevated skin flap was transilluminated to aid identification of an appropriate location for definitive urethrostomy that would not compromise the vasculature of the flap (ǠFig. 4). Sterile saline was instilled into the urinary bladder and expressed through the urethral remnant aiding identification of the lumen. Stay sutures were placed using 2 metric polypropylene to appose the flank skin fold advancement flap to the wound margins. Urethrostomy was performed by urethral spatulation and the urethral mucosa sutured to the dermis using 1.5 metric nylon q . A six French Foley indwelling urinary catheter r was placed (ǠFig. 5) and the cystostomy tube was removed. Potentiated amoxicillin s (20 mg/kg) was administered intravenously intraoperatively and three times daily postoperatively. Oral antibiotics were administered until day 37. Thirteen days following revision surgery, a small area of tissue necrosis was observed at the flank skin fold advancement flap margin, but it was not associated with the pre-pubic urethrostomy site. This was managed with open wound management and subsequent surgical closure.
Three months following definitive surgery, the cat developed mild moist superficial dermatitis of the peristomal and inguinal regions and medial thighs. This resolved following clipping of hair by the referring veterinarian and application of a barrier spray t .
Twelve months following presentation the cat was not having any problems. There had not been any episodes of urinary tract infections, urinary incontinence, or further moist superficial dermatitis. The cat had learned to posture appropriately to urinate and to clean the urethrostomy site.

Postoperative Care
Following each surgical procedure, postoperative analgesia was initially provided with methadone (0.2 mg/kg) every four hours for 24 hours followed by buprenorphine u (0.01 -0.02 mg/kg) every six hours.

Discussion
Prepubic urethrostomy is indicated when there is an insufficient length of normal urethra to perform a perineal urethrostomy or transpelvic urethrostomy (4,5).
Peristomal tissue necrosis due to urine extravasation following PPU has a reported incidence rate of up to 25% (2,4,5   A flank skin fold advancement flap has been elevated. Note that the surgical theatre light is being used to transilluminate the skin flap to identify a site for the definitive urethrostomy. Note also the Foley catheter entering the urethral remnant and that the wound has been omentalised through a paracostal laparotomy.  (4,6). However, the ventral abdominal tissue necrosis observed in the case reported here could potentially have been caused by urine extravasation immediately following trauma rather than post-PPU (2). Regardless of cause, urine induced tissue necrosis is challenging to manage due to the potential extent of infiltration of healthy tissue by noxious urine.
Successful management of urine induced proximal pelvic limb skin and muscle necrosis in a cat using VAC has been reported (7). Vacuum assisted closure was first described in 1993 by Fleischmann et al. and the first clinical trials of a commercially available device were reported by Argenta and Morykwas in 1997 (8)(9)(10). Vacuum assisted closure has had a major impact on management of complex wounds in human medicine and was first reported as a management option for complex wounds in veterinary medicine in 2007 (11). Proposed primary mechanisms of action include drawing of wound edges together, stabilisation of the wound environment, microdeformation of the wound surface, decrease in wound oedema and removal of exudate (12). Secondary effects may result in increased angiogenesis, earlier granulation tissue formation and a decrease in bacterial burden (12). Earlier granulation tissue provides an earlier barrier to infection and protection of the wound bed (13). Application of VAC also decreases frequency of dressing changes with an associated decrease in costs (14).
In the above case, we describe a salvage procedure following peristomal tissue necrosis after PPU. Due to the extent of necrosis, conventional wound management whilst retaining a urethrostomy was not possible. At this stage, salvage of the urinary tract by permanent urinary diversion via a tube cystostomy was a long-term option. However, up to 49% of animals with tube cystostomy develop complications (15). Major complications of tube cystostomy include patient removal of tube or tube displacement from the bladder, patient damaging the tube, uroperitoneum and urinary tract infection (15). As a result, we performed the novel technique of tube cystostomy and temporary ligation of the urethra in conjunction with VAC. The benefit of this was to remove the source of necrotising urine whilst also allowing for a definitive reconstruction and urethrostomy procedure at a later date. The use of VAC probably accelerated the progression of the wound environment to a stage where definitive surgical intervention was appropriate.
We ligated the urethral remnant as distally as possible and placed it within a Penrose drain in an attempt to prevent incorporation of the urethra into the bed of granulation tissue on the body wall. This was considered imperative to preserve sufficient urethral length for a tension free definitive urethrostomy. To the author's knowledge, this had not been described previously. While we did not experience any complications associated with this, it is acknowledged that leaving this in place for a protracted period could lead to development of a foreign body reaction.
The utilisation of the flank skin fold advancement flap in this case provided the most reliable closure option for the large 10 cm by 10 cm ventral abdominal mid-line granulation bed. The risk of compromising the flap's vasculature by creating the urethrostomy via an incision within the flap was decreased by transillumination of the flap to identify a site for urethrostomy.
In any case where a multitude of both novel and accepted treatments are utilised, it can be difficult to ascertain the contributions of each to the successful outcome, and it is so in this case. While urine induced subcutaneous tissue and skin necrosis frequently responds to more conventional methods of wound management, the use of VAC was felt to be beneficial in terms of reducing the frequency of dressing changes. The frequency of sedations or anaesthesia episodes required was also reduced, thus facilitating general management of the cat. Vacuum assisted closure has also been shown to promote the healing process and reduce the number of courses of antibiotics required, thus probably reducing the period of hospitalisation and the cost to the clients (16)(17)(18). Use of the flank skin fold advancement flap provided an adequate source of skin to cover the healthy granulation bed following VAC. The recipient wound bed was omentalised prior to closure in the expectation that omentalisation would provide a source of drainage and in-crease the likelihood of the advancement flap healing (19). Temporary urethral ligation and urinary diversion by tube cystostomy allowed adequate management of urinary output whilst retaining the ability for delayed definitive urethrostomy following successful wound management.
Temporary tube cystostomy in combination with temporary urethral ligation prior to performing delayed urethrostomy through a flank skin fold advancement flap presents a viable management option for patients with extensive ventral abdominal tissue necrosis.