Prognostic Factors for Successful Outcome Following Urethral Rupture in Dogs and Cats
Twenty dogs and 29 cats were identified with urethral rupture. Males predominated in both groups. The most common cause of urethral rupture in dogs was vehicular trauma, and in cats it was trauma associated with urethral obstruction and catheterization. Clinicopathological findings, type of surgical correction, time to surgery, type of urinary diversion, and duration of urinary diversion were not statistically associated with the outcome. In this study, the presence of multiple traumatic injuries was associated with a poor outcome.
Introduction
Urethral injuries occur in dogs and cats as a result of vehicular trauma, kicks, gunshot wounds, penetrating injuries, urinary calculi, or following iatrogenic trauma from catheterization or surgery.1–5 Urethral injuries are uncommon in both humans and small animals, and they require a high index of suspicion for diagnosis.6–9 The diagnostic test of choice is contrast radiography.9–12 Cystourethroscopy can also be used to visualize full or partial defects in the urinary bladder and urethra.13 Cystourethroscopy may be a viable technique for female dogs, but it is not viable for male dogs because of the long length of the male urethra and the need for a urethrostomy to be performed to facilitate the examination.14 Abdominocentesis is useful to diagnose uroperitoneum, which suggests a urethral rupture and may then be followed by contrast radiography, exploratory surgery, or necropsy to confirm the diagnosis.9
The most common complications of urethral rupture in humans and small animals are metabolic disturbances secondary to urine retention, tissue damage from urine extravasation into intrapelvic or subcutaneous tissues, urethral stricture formation, and urethrocutaneous fistula formation.1,15–18 A number of studies have been performed in small animals to determine the most effective method of urethral repair and which one results in the fewest complications.19,20 In general, urethral rupture by itself is not life threatening if treated appropriately, but it may be associated with other life-threatening injuries.16 The purpose of this retrospective study was to describe the signalment, clinical parameters, surgical repair procedures, urinary diversion techniques, outcomes, and factors associated with outcome in dogs and cats with urethral rupture.
Materials and Methods
A computer search of the medical records of all animals admitted to the Matthew J. Ryan Veterinary Hospital at the University of Pennsylvania from January 1986 to December 2003 was performed. Those animals with urethral disruption confirmed by either contrast radiography or direct visualization were included in the study. Medical records were reviewed, and the following information was recorded: signalment, cause of trauma, anatomical location of the urethral rupture, presence of multiple injuries, clinicopathological findings at time of admission (e.g., packed cell volume, total solids, serum creatinine, blood urea nitrogen [BUN], serum potassium, blood pH, serum bicarbonate concentrationa), time from presentation to surgery, method of surgical correction used (if applicable), method and duration of urinary diversion (i.e., insertion of a urethral catheter and/or cystostomy tube), and outcome. Follow-up information was obtained from the medical record or by telephone conversation with the owner. Survivors were defined as animals that survived to discharge, while animals that died or were euthanized in the hospital were considered nonsurvivors. Outcome was considered good if the animal survived and was free of complications associated with the urethral injury.
Statistical Analysis
Continuous variables (i.e., all clinicopathological data, age, time from admission to surgery, and duration of urinary diversion) were evaluated for normality by visual inspection of scatterplots and the Shapiro-Wilk test. Normally distributed continuous variables are described as a mean ± standard deviation, and comparisons between groups were made using the unpaired t-test. Nonparametric continuous variables are described using medians and ranges (minimum to maximum), and comparisons between two groups were done with the Mann-Whitney test. Comparisons among multiple groups (e.g., comparing time to surgery for the different types of surgery) were done using the Kruskal-Wallis test. The continuous variables presented in Tables 1 and 2 are described with medians and ranges, because some of the outcome groups were too small to fulfill the presumption of normality. Proportions, actual counts, and/or percentages were used to describe categorical data (i.e., sex/neuter status, types of trauma, location of urethral trauma, concurrent injuries, proportions of animals that had elevated BUN or creatinine, types of surgical correction, types of urinary diversion, and outcome), and the Fisher’s exact test was used to compare these types of data among groups. A P value <0.05 was considered significant. All statistical analyses were performed using a statistical software program.b
Results
Signalment
Twenty dogs and 29 cats were included in the study. Dog breeds included mixed-breed dogs (n=4), beagles (n=2), and one each of a miniature schnauzer, Jack Russell terrier, Chihuahua, Labrador retriever, English pointer, shih tzu, Weimaraner, German shepherd dog, Lhasa apso, miniature poodle, toy poodle, basset hound, Yorkshire terrier, and American cocker spaniel. Feline breeds included domestic shorthair cats (n=26), one Himalayan, and one Siamese. Breed was not recorded for one cat. The median age of dogs was 5.0 years (range 2 to 12 years). The median age of cats was 3.5 years (range 1 to 11 years). Males predominated in both groups, with 14 intact males, three neutered males, and three spayed females comprising the dogs. All of the cats were males. Twenty-six were neutered, and three were intact.
Clinical Findings
The most common cause of urethral trauma in dogs was vehicular trauma (n=14), followed by trauma from catheterization and/or urethral calculi (n=6). Trauma from urethral obstruction and catheterization was the most common cause of rupture in the cats (n=23), followed by unknown trauma (n=3), vehicular trauma (n=2), and trauma from a gunshot wound (n=1). Location of the urethral rupture was available for 12 male dogs and included the prostatic urethra (n=4), junction of the prostatic and membranous portions (n=5), membranous urethra (n=1) [see Figure], and the penile urethra (n=2). Location of the urethral rupture was not available for the other animals in this study. Concurrent injuries in dogs included multiple pelvic fractures (n=12), sacroiliac luxations (n=5), prostatic trauma (n=4), body wall herniation (n=3), prepubic tendon avulsion (n=2), femoral fracture (n=1), severe ligamentous damage to the stifle (n=1), coxofemoral luxation (n=1), neurological deficits in the hind limbs (n=1), splenic laceration (n=1), pulmonary contusions (n=1), and head trauma (n=1). Concurrent injuries in cats included perineal wounds (n=2), multiple pelvic fractures (n=1), sacroiliac luxation (n=1), as well as femoral (n=1), tibial (n=1), and sacral (n=1) fractures.
Tables 1 and 2 summarize the clinicopathological findings at the time of admission in the dogs and cats, respectively. Nine dogs in the study had elevated BUN (29 to 143 mg/dL; median 55 mg/dL; reference range 8 to 28 mg/dL), and seven dogs had increased creatinine levels (2.1 to 5.5 mg/dL; median 2.7 mg/dL; reference range 0.5 to 1.7 mg/dL). Sixteen cats had increased BUN (39 to 201 mg/dL; median 80 mg/dL; reference range 14 to 34 mg/dL) and increased creatinine (2.6 to 11.9 mg/dL; median 5.5 mg/dL; reference range 0.9 to 2.2 mg/dL). There were no statistically significant differences between survivors and nonsurvivors with respect to any of the clinicopathological findings [Tables 1, 2].
Surgical Correction
Time from admission to surgery for dogs ranged from 0 to 7 days (median 1.5 days), and for cats it ranged from 0 to 8 days (median 0.5 days). Time from admission to surgery was not significantly different between those that survived and those that died or were euthanized in the canine group (P=0.33) or feline group (P=0.34).
Surgical correction was performed in 15 dogs and 21 cats. Surgical correction consisted of primary urethral repair plus insertion of a urethral catheter (eight dogs, two cats); primary urethral repair plus insertion of a urethral catheter and cystostomy tube (one dog); primary urethral repair alone (one dog); cystostomy tube placement (one dog, five cats); cystostomy tube placement plus insertion of a urethral catheter (one dog, four cats); permanent urethrostomy (one cat); permanent urethrostomy plus insertion of a cystostomy tube (six cats); permanent urethrostomy plus placement of a urethral catheter (one dog, two cats); and permanent urethrostomy plus insertion of both a cystostomy tube and a urethral catheter (one cat). Four dogs had surgery that did not involve repair of the urethra, but they were included in the analysis of time to surgery since they were submitted to anesthesia. This may have affected the outcome results. The surgeries in these latter four dogs included cystotomy (n=2), cystotomy plus abdominal herniorrhaphy (n=1), and prostatic omentalization (n=1). Two dogs and four cats were euthanized without treatment. The type of surgical correction used was not significant with regard to survival for either dogs (P=0.71) or cats (P=0.11).
Urethral catheter placement alone (without surgical repair of the urethra) for urinary diversion was performed in three dogs and four cats. Urethral catheter insertion in conjunction with surgical repair was done in eight dogs and five cats. Cystostomy tube placement was done for urinary diversion in conjunction with surgical repair in two dogs and 15 cats. Both urethral catheter and cystostomy tube placement in conjunction with surgical repair were done in one dog. Combined urethral catheter and cystostomy tube placement alone (without surgical repair) were used in three dogs and one cat. The type of urinary diversion used was not significant between survivors and nonsurvivors in the dogs (P=0.053). Durations of urinary diversion ranged from 0 to 14 days (median 2.5 days) in dogs and 0 to 16 days (median 4 days) in cats. The duration of urinary diversion was not significant with regard to survival for dogs (P=0.68). Statistical analysis could not be performed for cats regarding the type or duration of urinary diversion, as only one cat in the nonsurvivor group had urinary diversion performed.
Outcomes
Thirteen dogs had good outcomes following surgery, with follow-up times ranging from 4 to 3650 days (median 36 days). Outcome was considered good if the animal survived to discharge and was free from complications associated with the urethral injury. One dog presented 35 days after surgery with stranguria secondary to a urethral stricture, and it was treated successfully with balloon dilatation of the stricture. Six of the dogs died or were euthanized within 14 days of presentation. Four of these dogs had surgical corrections, and two were not treated [Table 3]. All six dogs that succumbed had sustained multiple traumatic injuries. Twenty-four cats had good results, with follow-up times ranging from 3 days to 2738 days (median 48 days). Five cats were euthanized within the first 24 hours. Of these cats, four were euthanized without treatment, and three had sustained multiple injuries [Table 4]. Eleven of 49 animals in this study did not survive (eight were euthanized, three died). Of these 11 animals, eight (72%) experienced multiple traumatic injuries. Only 10 (27%) of the animals that survived had multiple traumatic injuries, which was statistically significant (P=0.011).
Discussion
Urethral trauma occurs rarely in dogs and cats.7,15 In a previous retrospective report of 600 animals involved in motor vehicle accidents, only two had urethral injuries, and both were associated with pubic fractures.7 In a second retrospective study of 281 cases of urinary tract trauma, 11% of the injuries were to the urethra, and most of these were associated with motor vehicle accidents.15 In a prospective study by Selcer, 100 animals with pelvic trauma were evaluated, of which five dogs had urethral ruptures with associated pubic fractures.8
In the retrospective study reported here, the most common cause of urethral injury in dogs was vehicular trauma; in cats, the most common cause was trauma from urethral calculi or attempts at urethral catheterization. It has been reported that urethral injury is more common in males but is possible in any animal with severe pelvic fractures or trauma to the other areas of the urethra.21 Most affected dogs and cats in the present study were males. Both the anatomy and temperament of males may contribute to their predominance in this study. The female urethra is less prone to injury, because the urethra is short and mobile and has no significant attachments to bone.16 Injuries to the female urethra are usually caused by sharp bone fragments from pelvic fractures.16 In cats, males may be affected more often, because they are more prone to urinary obstruction from calculi or mucous plugs owing to the small diameter of their urethra.18 With regard to temperament, intact male dogs predominated (14/20) in the study reported here. Intact male dogs may have more roaming behavior and subsequently have a higher risk for vehicular trauma.22 Of the 14 dogs with urethral injury secondary to vehicular trauma, 12 were intact males.
The canine male urethra is divided into prostatic, membranous, and cavernous portions. With pelvic fractures, most injuries are to the prostatic or membranous portions of the urethra, consistent with the locations of injuries identified in the study reported here.4 Urinary calculi as well as attempts to dislodge obstructive calculi can cause damage to any portion of the urethra, but injuries are more common in the penile portion and at the level of the ischial arch.21 This is consistent with the results of the current study, as the two urethral defects located in the penile portion of the urethra were in dogs that had urethral obstruction with subsequent urethral catheterization.
Clinicopathological findings were also evaluated in this study to determine if any parameters could be used as prognostic indicators for a successful outcome. Although there are no reported clinicopathological changes specific to animals with urethral injury, animals with urine retention secondary to urinary tract trauma are expected to be azotemic.9,10 Electrolyte disturbances including hyperkalemia, hyponatremia, and hypochloremia along with metabolic acidosis have also been reported in small animals.9,10 Similarly, animals that sustain a urethral injury that subsequently results in a urethral obstruction might also be presented with azotemia, metabolic acidosis, and hyperkalemia.23 While a number of animals in the current study were azotemic, a significant difference was not seen between the animals that survived and those that did not when their clinicopathological parameters were compared. One explanation for the animals that were not azotemic may be that they were evaluated before clinicopathological changes developed, or they had their urinary obstruction relieved by the referring veterinarian prior to presentation.
Surgical repair of the urethra in this study consisted of primary anastomosis of the urethra or permanent urethrostomy. These procedures were performed with and without urinary diversion. A previous study by Layton et al. examined three techniques used for urethral anastomosis, namely sutured anastomosis with no urethral catheter, sutured anastomosis with a urethral catheter, and a urethral catheter with no sutures. Results of that study showed that the sutured anastomosis over a urethral catheter resulted in fewer strictures.19 In the study reported here, permanent urethrostomy was performed in one dog and nine cats, and it appeared to be a viable option for dealing with urethral injury.18
Urinary diversion was a component of therapy for the animals in this study. Previous studies have shown that the uroepithelium can bridge a defect within 3 to 21 days when urine is diverted away from the surgical site or site of injury.1–4,17 All dogs that survived but one (case no. 16) had urinary diversion from insertion of a cystostomy tube, urethral catheter, or both. In the dog that did not have urinary diversion, a primary repair of the urethra was performed. Two dogs (case nos. 8, 13) that did not have urinary diversion were euthanized without any form of treatment.
One of the most important factors affecting urethral healing is urine extravasation.4,18 Urine in contact with the periurethral tissues causes delayed wound healing and periurethral fibrosis.4,18 In a study by Cooley, et al., 15 dogs were placed in one of three treatment groups. All dogs had a primary urethral anastomosis and either a cystostomy tube, urethral catheter, or both for seven days, and no differences were found in outcomes among any of the groups.20 In the study reported here, all animals (except one dog and one cat) that survived had some form of urinary diversion, and this may have contributed to the successful outcomes of these animals.
Complications of urethral injury include stricture formation, incontinence, urethrocutaneous fistula formation, and urine leakage with resultant tissue damage.1,15 Long-term complications were minimal in the current study, with only one dog (case no. 4) developing stranguria secondary to stricture formation. In this dog, the stricture may have been more likely to form because the urine was contaminated from a prostatic abscess. Previous studies have shown that infected urine can promote inflammation at the site of injury and cause increased fibrosis and stricture formation.19 This dog responded favorably to balloon dilatation of the stricture. It is possible that a number of animals in the study had some luminal narrowing secondary to stricture formation, but they did not demonstrate clinical signs of stranguria or tenesmus. It has been shown that a decrease in lumen size >60% is necessary before animals may show tenesmus or stranguria.20 Unfortunately, repeat contrast studies were not performed on any of the study animals that remained clinically normal.
In this study, multiple traumatic injuries were associated with a poor outcome. Animals with urethral injuries have often been hit by cars and may suffer severe injuries, including pulmonary contusions, fractures, or diaphragmatic or body wall hernias.24 Animals with multiple severe injuries may be more likely to be euthanized because of a poor prognosis or the expense of treatment. In the authors’ experience, these animals may also be more likely to die in the perioperative period from their concurrent injuries.
In the present study, an attempt was made to determine prognostic indicators for successful outcomes in dogs and cats with urethral rupture, but the only prognostic indicator found was the presence of multiple injuries. Animals that survived the perioperative period had a favorable prognosis. It is possible that with a larger number of study animals, other prognostic factors could be elucidated. Other limitations of this study were the retrospective nature of the study, which limited the information gathered from each case, and the short follow-up time available for some of the animals. Other limitations were the variables introduced by having multiple clinicians involved in the diagnosis, stabilization, and surgical repair of the animals in the study.
Conclusion
Twenty dogs and 29 cats with urethral ruptures were retrospectively evaluated. Males predominated in both species. Urethral rupture was most commonly caused by vehicular trauma in dogs and by urethral obstruction and catheterization in cats. The presence of multiple traumatic injuries was associated with a poor outcome for both dogs and cats. A future prospective study with a larger number of animals, standardized diagnostics and treatment protocols, and longer follow-up times may help to elucidate other prognostic factors. Results of the current study may be used to counsel owners that dogs and cats with urethral rupture have a favorable prognosis in the absence of concurrent multiple injuries.
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Citation: Journal of the American Animal Hospital Association 42, 2; 10.5326/0420136
Lateral abdominal radiograph of a retrograde positive-contrast cystourethrogram of a 3-year-old, male beagle (case no. 1), demonstrating a defect in the membranous portion of the urethra and leakage of contrast material (arrows) into the periurethral tissues that developed from urethral transection following motor vehicle trauma.
