Perineal Hernia

Perineal hernia (PH) results from weakness of muscles of the pelvic diaphragm. It occurs most likely in older male dogs, where its prevalence ranges from 0.1 to 0.4% from different hospital admissions [1,2]. It has also been described in cats, but one study describes only 40 cases in 12 years in three major American referral centers [3]. Some cases have also been mentioned in the female dog.

Clinical signs include straining to defecate and, less frequently, straining to urinate. Some other signs such as fecal incontinence, urinary incontinence, and flatulence have also been mentioned [1-17].

The clinical diagnosis is based on appearance of a perineal swelling, most often right-sided or bilateral. A rectal examination demonstrates the presence of accumulated feces in an abnormally enlarged rectum. When the rectum is empty, the hernia may be difficult to diagnose. In these cases, the ability to push the finger through an enlarged rectum toward the sacrotuberous ligament demonstrates the loss of muscular support to the rectum wall and thus is diagnostic for perineal hernia |1,4,5] Occasionally, an acute soft-tissue swelling increases the perineal deformation unilaterally. In these cases, a perineal cystocentesis usually confirms the diagnosis of an associated retroflexed bladder [1,15]. In most cases, besides the rectal wall deformity, periprostatic fat, omentum, digestive loops, or prostate may fill the perineal cavity [1,2,18].

Causal Factors for Perineal Hernia

Predisposition

Breeds

Although breed over-representation has been mentioned for the Boston terrier, Pekingese, Boxer, Collies, and Old English sheepdogs [1,2,12], this predisposition was not found in two other retrospective studies [16,17] where Yorkshire terriers, Cotons, Bichons, German Shepherds, and Mixed-breeds have been the most common breeds encountered.

Male/Female

Perineal hernia occurs almost exclusively in male dogs. Some authors have shown that the levator ani muscle is larger and stronger in the female compared with the male dog to support parturition, thus explaining the low number of perineal hernias in the female [19]. However, when the weight of the pelvic diaphragm muscles was compared in some predisposed breeds (Corgie, Boxer) [1,2] to the weight of the same muscles in the Greyhound, no significant difference was found [19]. Therefore, based solely on the muscle weight, it is difficult to understand why perineal hernia occurs rarely in female dogs [2].

Age

Perineal hernia occurs most commonly in dogs from 7 to 9 years of age [1,5,12]. Whether the age is associated with muscle weakness, prostatic disease, or any other underlying disease remains unknown [15,20,21].

Side of the Hernias

Among different studies, 60% of perineal hernias were unilateral and 40% bilateral [5,10-17]. Among the unilateral hernias, almost 70% were right-sided. Studies have failed to demonstrate a relative weakness of the pelvic diaphragm muscles of the right side. On rectal examination of unilateral hernias, a contralateral weakness is often encountered. Failure to recognize this weakness and to reconstruct adequately this contralateral side makes it prone to future hernia [17].

Increased Abdominal and Perineal Pressure

Chronic constipation resulting from bad feeding habits is usually associated with increased defecating efforts, which in turn, can increase abdominal and perineal pressure [17,18,22,23]. In cats, most cases were bilateral and associated with chronic constipation, megacolon, stranguria, or perineal urethrostomy surgery [3]. Increased abdominal pressure during coughing could be one predisposing factor in female dogs and in older male dogs prone to cardiac insufficiency.

Muscular Weakness and Atrophy

Perineal herniation commonly occurs between the external anal sphincter and the levator ani muscle and, more rarely, between the levator ani muscle and the coccygeal muscles. Frequently, the cranial remnants of the levator ani can be found close to the external anal sphincter or to the external coccygeal muscle. In severe cases, muscle atrophy will involve not only the levator ani muscle but also the external coccygeus, the internal obturator muscle, and the external anal sphincter [1,2,18,24]. Biopsy specimens of the levator ani muscle fibers of dogs suffering from perineal hernia have shown atrophy of neurologic origin [24], but it remains unclear whether this atrophy is an expression of aging, neurologic disease, or excessive pressure.

Hormonal Imbalance

Androgen

Perineal hernias have frequently been associated with testicular tumors (2% of sertolinomas, 15% of interstitial tumors, 19% of seminomas, and 11% of mixed tumors) [25], which suggested an association between hormonal imbalance and pelvic diaphragm muscle atrophy. Currently, no influence of the androgen concentration has been demonstrated, although, in the rat, androgen receptors have been found in the levator ani muscle. Similar studies in the canine have failed to demonstrate any relation between testosterone levels and muscular fiber size [19,26,27]. In one study, the recurrence rate in castrated animals was 2.7 times less than in intact animals [2]. This is one of the reasons why castration is recommended as an adjunct therapy for perineal hernia.

Role of Prostate

The presence of relaxin in the canine prostate was evidenced and the hypothesis of relaxin being involved in perineal hernia formation in male dogs was tested. Based on preliminary results, relaxin of prostatic origin leaking from periprostatic cysts, usually seen in the perineum of affected dogs, is a possible factor in local connective tissue weakening and subsequently in perineal hernia formation [28].

Different studies confirm that dogs with perineal hernia are prone to concurrent prostatic disease (range 10 to 51%) [12,14-17,29,30]. In one study where ultrasonographic prostatic assessment was performed before any perineal hernia surgery, prostatic lesions were present in 17 dogs (41%); in 8 dogs (19.5%), prostatic disease had to be specifically treated surgically [15]. In another study on 41 bilateral or complicated hernias, 9 prostatic surgeries (omentalization or perineal cyst resection) were performed [17]. Given the high frequency of prostatic disease associated with perineal hernia, an ultrasound evaluation of the prostate is recommended prior to surgery. It remains unclear whether both diseases occur in the same type of patients (breed, age, and sex) or if a significant correlation does exist [15-17,21].

Pathogenesis

Deterioration of the levator ani muscle results in a progressive loss of rectal wall support. The fissure between the external anal sphincter muscle and the pubocaudal part of the levator ani muscle progressively enlarges. Retroperitoneal fat naturally progresses through this fissure. The loss of muscular support and the progression of defecating efforts increase the chances of the rectum to progressively fill this new space into the perineal cavity. Then, because of lack of continuity of the rectum with the anus, feces cannot be expelled and defecating efforts even increase. Secondary rectal dilation occurs [1,12,15,17,21]. During this process, continual straining to defecate progressively enlarges the rectal dilatation and further weakens the pelvic diaphragm muscles [17]. Finally, persistent straining associated with a huge rectal dilatation and hernia can even promote secondary herniation of the prostate and retroflexion of the bladder into the perineal cavity.

Rectal Diseases

Rectal lesions associated with perineal hernia have previously been characterized as deviation (a change in rectal orientation from the midline), sacculation (enlargement not associated with tearing of the muscular wall), or diverticulum (protrusion of rectal mucosa through the muscular layers of the rectal wall) [12,14,17,21]. Because differentiation between rectal deviation, sacculation, and diverticulum appears difficult clinically or radiographically [12,13,21] a grading for the rectal dilatation was proposed [17]. In this study, a simple deviation with no dilatation was a grade 1, a mild rectal dilatation (asymmetric dilatation with fecal accumulation without visible perineal deformation) was a grade 2, and a severe rectal dilatation (asymmetric dilatation with a visible bulge of the perineum and a large amount of fecal accumulation and impaction) was a grade 3.

Bladder Retroflexion

Bladder retroflexion occurred in 12 to 29% of dogs [6,8,10,12,15-17,29,31]. In cases of retroflexion, the bladder rotates at least 180° around its neck. Although this finding was not statistically significant in all studies [17], perineal hernias with bladder retroflexion carried a higher mortality rate (30%) and a worse prognosis than those without [6,10,12]. Following retroflexion, several complications can be encountered. Acute renal failure can occur secondary to complete urethral occlusion, bladder necrosis owing to occlusion of the urogenital arteries [12], and overall, partial, total, temporary, or definitive loss of urinary continence can occur [12,17].

Perineal Hernia Grading

In order to propose guidelines for surgical treatment, some authors have graded perineal hernias as unilateral, bilateral, and complicated. A perineal hernia was defined as complicated if it met the following criteria: recurrence of PH, unilateral PH with a severe (grade 3) rectal dilatation, PH with a concurrent surgical prostatic disease, and PH with retroflexed bladder [15,16,17].

Considerations for Treatment

Closure of the Pelvic Diaphragm

Current approaches to treatment of perineal hernia rely on closure of the pelvic diaphragm. Because muscle appositional techniques resulted in excessive tension on the external anal sphincter, muscle transposition techniques were developed using the superficial gluteal muscle [7,8], internal obturator muscle [8-12], semitendinosus muscle flap [32], or a combination of internal obturator muscle with superficial gluteal muscle flap [13]. Filling the defect with stainless steel, polypropylene mesh [33,34], porcine intestinal submucosa [35,36], and with fascia lata have been suggested [37]. Presently, the internal obturator flap with tenotomy is the most popular and seemingly the most appropriate technique for most cases of herniorraphy. In cases of severe muscle loss, we have successfully used the superficial gluteal muscle flap or the fascia lata free flaps.

Laparotomy in the Treatment of Perineal Hernia

Besides rupture of the pelvic diaphragm, rectal disease, bladder retroflexion, and prostatic disease often occur concurrently [6,12,14-17,21,29-31]. They contribute to the severity of perineal hernia, and may even discourage further treatment. After a report by Bilbrey et al in 1990 [29], some authors studied the incidence of rectal, prostatic, and bladder diseases associated with perineal hernia [14-17,20]. Since 1993 they have developed a "2-step protocol", where laparotomy was performed as the initial stage of repair in bilateral or complicated perineal hernia (recurrence of perineal hernia, unilateral perineal hernia with a grade 3 rectal dilatation, perineal hernia with a concurrent surgical prostatic disease, and perineal hernia with retroflexed bladder). During laparotomy, colopexy and cysto- or vas deferens-pexy and, if needed, prostatic surgery, are performed, and a perineal herniorraphy using an internal obturator muscle flap transposition [15-17] is performed 2 to 7 days later. Results compare favorably with those of previous studies [6,9-13]. Satisfactory results using colopexy and cysto- or vas deferens-pexy as sole or adjunctive treatment for perineal hernia have also been reported by others [14,29,31].

Rationale For A Two-Step Protocol

Colopexy resolves rectal dilatation or deviation, vas deferens-pexy stabilizes the prostate, and cystopexy prevents abnormal motion of the bladder so that the perineal space becomes free of viscera after the abdominal surgery. At subsequent herniorraphy, perineal inflammation has resolved and the hernia is empty, which allows improved observation of important local anatomic structures such as the pelvic diaphragm muscles, pudendal and caudal rectal nerves and artery, internal obturator muscle and tendon, and rectal wall. This facilitates hernia repair (Fig. 13-1) [15,17]. Then guidelines for perineal repair can be proposed (Table 13-1).

Figure 13-1. A 7-year-old mixed-breed dog with left perineal hernia and grade 3 rectal disease. Note the appearance of the perineum before (A) and after (B) colo- and cystopexy.

Prognosis, Complication Rates and Causes

Prognosis and complication rates have been published. They depend on the severity of the hernia, associated disease, surgeon's experience, and surgical techniques (Table 13-2).

Colo-Recto-Anal Abnormalities

Preoperatively, external anal sphincter mechanism incompetence is rare. However, chronic distension of the rectal wall and chronic straining may weaken the external sphincter fibers. Whenever incompetence is suspected, electromyography of the external sphincter should be recommended prior to surgery. Although postoperative fecal incontinence and rectal prolapse have been described respectively in 3 to 15% [10,12,30] and 7 to 42% [10,12] of dogs with PH, none of the dogs sustaining a laparotomy as a first-step procedure experienced this complication [17]. When recorded, persistent postoperative tenesmus has been reported to occur in to 2 to 50% of dogs [10,12,17]. Causes of persistent postoperative tenesmus have not been determined, although rectal deformation associated with persistent rectocolitis has been suggested [12]. Colonic or rectal motility disorders can also be associated with long-term straining [22,23]. This could explain poor rectal emptying in some patients with good perineal reconstruction [17].

Urinary Dribbling

Postoperative urinary incontinence has been described in 4 to 8% of dogs with perineal hernia [6,10,12,14,17]. Suggested mechanisms involve acute traction on the hypogastric and pelvic nerves or secondary deterioration of the detrusor muscle owing to retroflexion [6,10,12,30]. In one study [17] 15 dogs (36%) presented with urine dribbling after surgery; 8 resolved within the first 6 months, but 7 (17%) had permanent dribbling. Possible associations between prostatic disease, bladder malposition as well as vas deferens- or cystopexy and urine dribbling remain to be determined.

Perineal Wound Infection

Perineal wound infection is the most common complication described after perineal hernia repair, ranging from 5 to 45% [9-13,17,30]. Absorbable monofilament suture material, perioperative antibiotics, and anal closure are used to decrease the risks of postoperative infection [10,12,30,38]. Although laparoscopic colo- and vas deferens-pexy have been suggested [39], these have been discouraged by some authors because of the high rate of septic complications at the colopexy site [16,17].