Iatrogenic proximal urethral obstruction after inadvertent prostatectomy during bilateral perineal herniorrhaphy in a dog

Abstract

Proximal urethral obstruction was diagnosed 2 days after bilateral perineal herniorrhaphy in a 12-year-old male Pomeranian-cross dog. The obstruction was caused by ligation of the proximal urethra during resection of a presumed paraprostatic cyst. Surgical repair involved reconstruction of the urethra and bladder wall, but urinary incontinence persisted.

A 4.4 kg, 12-year-old, castrated male Pomeranian-cross was referred to the Veterinary Teaching Hospital, Western College of Veterinary Medicine (WCVM-VTH), for dysuria after bilateral perineal herniorrhaphy. The dog had been presented to the referring veterinarian 3 wk earlier with a complaint of dyschezia, at which time a diagnosis of bilateral perineal hernia was made. Castration and bilateral perineal herniorrhaphy were performed by the referring veterinarian on the following day, using a standard internal obturator transposition technique (1). In the left hernia, small intestine, periprostatic fat, and a suspected paraprostatic cyst were found. The small intestine was repositioned and the periprostatic fat partially amputated. The cyst was ligated and resected.

The dog was discharged 24 h after surgery (day 3), but was returned 2 d later (day 5) with a complaint of restlessness, straining, vomiting, anorexia, and failure to pass urine or feces. The bladder was distended and could not be expressed. Substantial resistance was noted at the level of the prostate during retrograde urinary catheterization. Catheterization appeared to be successful, as approximately 100 mL of dark brown urine and blood clots were removed through the catheter once in place. Urinalysis showed a specific gravity of 1.020, red blood cells too numerous to count, 3 to 4 cellular casts, and 10 to 15 leukocytes per high-powered field (at 400X magnification). Hematologic study and biochemical analysis showed a severe leukocytosis (42.0 × 10⁹/L; reference range, 6.0 to 16.9 × 10⁹/L), elevated urea (> 46.41 mmol/L; reference range, 2.50 to 9.64 mmol/L), and elevated creatinine (502 μmol/L; reference range, 44 to 159 μmol/L). Potassium was within normal limits (4.77 mmol/L; reference range, 3.50 to 5.80 mmol/L).

Intravenous fluids, cefazolin (Cefazolin Sodium; Novopharm, Toronto, Ontario), 25 mg/kg bodyweight (BW), IV, q8h, and enrofloxacin (Baytril; Bayer, Etobicoke, Ontario), 2.5 mg/kg BW, SC, q12h, were administered and the urinary catheter was maintained. On day 10, the dog ate a small amount of canned food, but was depressed and still vomited occasionally. On reanalysis, urea, creatinine, and the leukogram were within normal limits. On day 11, the urethral catheter was removed. Small amounts of dribbling urine were noted and treatment with phenoxybenzamine was initiated (Dibenzylen; SmithKline Beecham Pharmaceuticals, Philadelphia, Pennsylvania, USA), 5 mg, PO, q12h.

Dysuria and stranguria continued, and on day 17 an exploratory laparotomy was performed by the referring veterinarian. A stricture was noted at the level of the bladder trigone, and a Y-V plasty was attempted. Biopsy of the bladder wall and trigone demonstrated inflammation and scarring associated with suture material, and extensive tearing and scarring of muscle fibers in the bladder wall. Because clinical signs recurred after surgery, an indwelling urinary catheter was placed, and the dog was referred to the WCVM for further evaluation.

Physical examination upon presentation to the WCVM revealed an intact herniorrhaphy, poor anal tone, intact perineal sensation, and absence of a perineal reflex. At this time, the dog was noted to be fecally incontinent. Laboratory analysis revealed a normal hemogram, slight elevations of urea (11.3 mmol/L; reference range, 3.0 to 10.5 mmol/L) and alkaline phosphatase (178 U/L; reference range, 12 to 106 U/L), and a mild decrease in albumin (28 g/L; reference range, 29 to 38 g/L). Urine specific gravity was 1.019, suggesting possible renal compromise in the face of elevated urea. Complete urethral obstruction at the level of the cranial pubis was confirmed on retrograde urethrography (Figure 1), and surgical reconstruction was planned. Although the results of urine culture were negative, the dog was maintained on prophylactic cephalexin (Novolexin 125; Novopharm), 30 mg/kg BW, PO, q12h, in preparation for surgical exploration.

Figure 1. Contrast cystourethrogram demonstrating obstruction of the urethra just cranial to the pubis (Arrow).

The dog was premedicated with hydromorphone (Hydromorphone; Sabex, Boucherville, Quebec), 0.1 mg/kg BW, IM, and midazolam (Midazolam; Sabex), 0.2 mg/kg BW, IM, induced with thiopental (Pentothal; Abbot Laboratories, Montreal, Quebec), 10 mg/kg BW, IV, to effect, and maintained on isoflurane (Isoflurane; Technilab, Mirabel, Quebec) and oxygen. Epidural morphine (Morphine Sulfate; Sabex), 0.01 mg/kg BW in 1.0 mL of saline was administered before surgery. Surgical findings included thickening of the bladder and proximal urethra and inflammation of the bladder serosa. A 1-cm bridge of mature scar tissue was found interposed between the proximal urethra and bladder neck, where the prostate would normally reside. The prostate and prostatic urethra were not present at this location. At this time, an incision was made into the ventral bladder wall and continued distally into the proximal urethra. The previously placed urinary catheter was noted to have been iatrogenically placed through a tear in the proximal urethra and into the bladder neck. Interposing scar tissue was resected, avoiding full thickness resection dorsally in an attempt to spare neurovascular structures. Urethrotrigonal anastamosis was accomplished by using 4-0 polydioxanone suture material (PDS II; Ethicon, Somerville, New Jersey, USA) in a simple interrupted pattern. The bladder was closed using 4-0 polydioxanone (PDS II; Ethicon) in a simple continuous pattern. An 8-French Foley prepubic cystostomy catheter was placed through a window in the abdominal wall and into the ventral bladder (2), prior to routine abdominal closure.

Closed urine collection through the prepubic catheter was continued following surgery. A contrast cystourethrogram, performed 4 d after surgery by infusing renografin (Renografin 76; Bracco Diagnostics, Mississauga, Ontario) through the prepubic catheter, showed patency of the anastamosis and no evidence of leakage. At this time, the prepubic catheter was capped to assess urinary function. Urine flowed well, but the dog had no control of micturition. Six days after surgery at the WCVM, the prepubic urinary catheter was removed. Intermittent conscious micturition was subsequently noted, although continuous urinary incontinence remained. Antibiotic therapy was discontinued and the dog was discharged from the WCVM, 8 d after surgery.

Five months after surgery, the dog was doing well, had urinalysis and biochemical results within normal limits, had gained 0.7 kg BW, and was fecally continent. Conscious micturition was noted intermittently, although continuous urinary incontinence persisted in the form of dribbling urine.

Perineal hernias may contain a variety of anatomic structures. In one study, the prostate gland was within the hernial contents in 4 of 32 dogs (3). In the same study, a paraprostatic cyst was noted in 1 of 14 prostates examined (3). The prostate is susceptible to a variety of diseases, many of which require surgical treatment (4). Prostatic cysts, categorized as prostatic retention cysts or paraprostatic cysts (5), are uncommon as a proportion of prostatic disease (approximately 2.6% to 5.3%) (6). Total prostatectomy, marsupialization and drainage, and drainage accompanied by surgical resection have all been described with varying success for the management of prostatic cysts (4,6). Partial resection of prostatic cysts followed by omentalization has recently been shown to be an effective method of surgical repair that may be associated with fewer complications (5).

Numerous surgical complications have been reported after perineal herniorrhaphy, including recurrence, dehiscence, infection, urinary and fecal incontinence, sciatic nerve damage, and rectal prolapse (1,3,7). Urinary incontinence is relatively rare and is usually a transient problem following retroflexion of the bladder into the hernia (3,7,8,9).

Complete prostatectomy and ligation of the proximal urethra was inadvertently performed while attempting resection of a presumed paraprostatic cyst in this dog. Discontinuity of the prostatic urethra necessitated surgical reconstruction of the trigonal-urethral anatomy. Trigonal anatomy was severely disrupted in this case, effectively damaging neurovascular pathways to a point at which they could not be repaired. Postoperative urinary diversion via prepubic urinary catheterization lowers the risk of urine leakage and minimizes the inflammatory effects of urine at the site of anastamosis (2). Capping the catheter allows the surgeon to evaluate urethral patency and control of micturition during the healing process.

Urinary incontinence in this dog likely resulted from iatrogenic sympathetic injury, as well as loss of normal trigonal muscle anatomy. The pudendal (somatic), hypogastric (sympathetic), and pelvic (parasympathetic) nerves innervate the bladder, prostate, and urethra, respectively (10). Perineal sensation and purposeful posturing by this dog to urinate suggest that somatic innervation was intact in this dog. Also, the presence of urinary bladder tone supports preserved parasympathetic innervation. Fecal incontinence following herniorrhaphy, as seen in this case, may result from damage to the pudendal or caudal rectal nerves, or to the external anal sphincter (1).

Perineal herniorrhaphy is challenging in that the perineal musculature, pelvic innervation, and blood supply are all at risk of iatrogenic damage. Additionally, organs located within the hernia can be injured, if careful dissection and proper tissue handling techniques are not used. In this dog, failure to identify the prostate gland and urethra prior to resection of the presumed paraprostatic cyst resulted in inadvertent urethral resection, urinary obstruction, and eventual urinary incontinence. It is prudent to catheterize the urethra prior to surgery to assist in its identification (7). Accurate identification of anatomical structures and meticulous dissection are required to avoid iatrogenic complications, as seen in this dog. CVJ