The pelvic diaphragm provides support to the pelvic outlet. It is comprised of the levator ani muscles, coccygeus muscles, external anal sphincter and fascia. Perineal herniation occurs when the components of the pelvic diaphragm weaken and separate, allowing caudal dilatation and deviation of the rectum and in some cases caudal protrusion of abdominal organs including the prostate, urinary bladder and intestine. This leads to accumulation of feces in the dilated/deviated rectum and typically constipation and straining to defecate. Uni- or bilateral swelling of the perineal region often also occurs. If the urinary bladder retroflexes into the hernia, stranguria may occur.
Perineal hernias have a reported prevalence of 0.1-0.4% in dogs and are uncommon in cats. Older, intact male dogs are most commonly affected, accounting for 83-93% of cases. Perineal herniation has been reported in dogs between the ages of 7-13 years with most falling between 7-9 years of age. Predisposition to perineal herniation has been reported in Pekingese, Boston Terriers, Corgis, Boxers, Poodles, Bouvier des Flandres and Old English Sheepdog breeds, but the disease is also commonly seen in mixed breed dogs.
The underlying etiology of perineal hernias is unknown and is likely multifactorial. Congenital predisposition, rectal abnormalities such as deviation or diverticulum, hormonal influences, prostatic disease and/or enlargement, and neurogenic muscle atrophy have all been implicated as potential causative factors. Conditions that lead to chronic straining, such as chronic constipation, anal sacculitis, cystitis or prostatic disease, could place stress on the pelvic diaphragm, leading to weakness and herniation. 25-59% of dogs with perineal herniation have concurrent prostatic disease. The higher prevalence in intact male dogs suggests hormones may have a role in this disease process.
Perineal hernias may be unilateral (47-66%) or bilateral. Right-sided herniation is most common if the condition is unilateral (59-84%). In unilateral cases, rectal examination often reveals weakness of the contralateral side and progression to bilateral herniation may occur. Bladder retroflexion has been reported in 20-29% of cases. If the bladder becomes entrapped and obstructed, azotemia and metabolic changes may occur, and the obstruction must be corrected immediately.
Diagnosis is made via digital rectal examination. On rectal exam, when perineal herniation is present, the examiner's finger can be easily extended to the side of herniation and palpated just below the perineal skin. Abdominal radiographs, contrast cystography and abdominal ultrasound may also be performed to determine the contents of the hernia, position of the urinary bladder and condition of the prostate.
Conservative management consisting of a diet high in fiber and moisture content, stool softeners and intermittent evacuation of feces from the dilated/deviated rectum, may be tried but is not successful long-term. Surgical repair of the hernia is the treatment of choice. A number of herniorrhaphy techniques exist including traditional apposition of pelvic diaphragm structures, internal obturator muscle transposition, superficial gluteal muscle transposition, and the use of prosthetic or biomaterial implants such as polypropylene mesh or Porcine Small-Intestinal Submucosa. Currently internal obturator muscle transposition is the technique of choice of most surgeons in most cases. Prior to surgery, CBC, chemistry panel and urinalysis should be performed to assess the patient's anesthetic status and look for concurrent illnesses. If the urinary bladder is involved, azotemia and metabolic changes may be noted. Urine culture should be considered in cases with concurrent cystitis. Enemas are not recommended within 24 hours of surgery as these increases the risk of contamination of the surgical site with liquid feces.
For internal obturator muscle transposition, an incision is made over the hernia swelling a few centimeters lateral to the anus. The internal obturator muscle is elevated from the dorsal surface of the ischium and used to fortify the hernia defect. The transposed internal obturator muscle is sutured to surrounding structures including the levator ani, coccygeus, external anal sphincter and in some cases the sacrotuberous ligament, thereby recreating the pelvic diaphragm. Severe or complicated perineal hernias are those in which rectal dilatation is severe, concurrent prostatic disease exists, the urinary bladder is retroflexed or previous repair of the hernia has been attempted and failed. In severe or complicated perineal hernias, colopexy, cystopexy and vas deferens pexy with castration should be considered. These procedures are performed through a ventral midline abdominal approach and may be performed under the same anesthetic event as the primary hernia repair or may be performed 2-7 days prior to primary repair. With colopexy, cranial tension is applied to the colon and the colon is pexied to the body wall in the cranial position in order to decrease dilatation and deviation of the rectum within the perineal hernia. Similarly cystopexy or vas deferens pexy allows for repositioning of the urinary bladder and prostate eliminating pressure on the hernia repair by these organs.
Most surgeons advocate castration at the time of hernia repair to decrease risk of postoperative hernia recurrence. Studies have shown that intact dogs have 2.7 times greater risk of recurrence than castrated dogs and that castration at the time of hernia repair decreases the risk of recurrence from 43% to 23%.
Post-operative treatment includes perioperative antibiotics, a low residue diet, and stool softeners as needed to decrease straining when defecating. Dogs should wear an e-collar to prevent licking of the incision and scooting should be discouraged.
The overall complication rate with internal obturator muscle transposition has been reported as 19-45%. Complications seen with perineal hernia repair include:
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- incision infection (6.4-45%)
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- urinary dysfunction
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- seroma
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- rectal prolapse (2-13%, less common with colopexy)
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- dyschezia
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- rectocutaneous or anal sac fistulation
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- tenesmus
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- sciatic nerve paralysis
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- fecal incontinence
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- recurrence
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If fecal incontinence occurs, it may be temporary from injury to the pudendal nerve or stretching of the external anal sphincter muscle. Permanent fecal incontinence has been reported in less than 15% of cases. Bladder atony has been reported in 18-29% of cases with bladder retroflexion and may be permanent or temporary. Postoperative urine dribbling was reported in 37% of complicated perineal hernia cases and was permanent in 17%. Tenesmus occurs commonly but is typically temporary. Tenesmus may increase the risk of recurrence.
Recurrence has been reported in 0-70% of cases overall. Recurrence of 0-36% has been reported following internal obturator muscle transposition. Surgeon experience has been shown to have a significant impact on recurrence rates with 10% recurrence reported when an experienced surgeon performed the repair and 70% recurrence reported for inexperienced surgeons. Recurrence is greater if a previous repair has been performed and failed (83%) than if no previous repair has been performed (43%).
References:
1.
AronsonLR: Rectum, Anus, and Perineum. In Tobias KM, Johnston SA, editors: Veterinary Surgery Small Animal, St Louis, 2012, Elsevier, pp1564-1600.
2.
Shaughnessy M, Monnet E: Internal obturator muscle transposition for treatment of perineal hernia in dogs: 34 cases (1998-2012). JAVMA 2015 Feb 1; 246(3):321-6.
Miriam Talaat, DVM, DACVS