Perineal hernias or ruptures are mostly seen in the middle aged to older entire male dog, though they are also reported in bitches and in the cat. The aetiology remains unclear but is associated with degenerative changes in the muscles of the pelvic diaphragm. Many factors have been implicated in the aetiopathogenesis but none has been fully substantiated. They include prostatomegaly, reduced numbers of androgen receptors in the levator ani and coccygeus muscles, rectal sacculation (most likely to be secondary to herniation), colitis and docking.

Four types of perineal hernia have been reported in dogs, but the hernia is usually caudal and located between the levator ani and coccygeus muscles and the external anal sphincter muscle.

With the loss of lateral support, there is progressive rectal deviation, which leads to enlargement. Unilaterally, this is termed sacculation, whilst the bilateral disease is termed dilatation. True rectal diverticula with rectal mucosa protruding through the rectal musculature are extremely rare. Hernias may be complicated by inclusion of pelvic and peritoneal fat, loops of small intestine, prostate gland, paraprostatic or prostatic cysts and, in severe cases, by retroflexion of the bladder.

Diagnosis of perineal hernias is confirmed by rectal examination, where sacculation and lack of lateral rectal wall support are noted. Contrast radiography or ultrasonography is of use to confirm a retroflexed bladder and aid in the diagnosis of concurrent prostatic disease.

Due to the risk of bladder involvement, all perineal hernias should be managed surgically by reconstruction of the pelvic diaphragm. In those cases that have bladder retroflexion, renal and electrolyte status should be assessed and corrected by fluid therapy before undertaking surgery. If urinary catheterization is not possible, relief can be gained by perineal cystocentesis. Where there is preoperative bladder retroflexion, replacement into the abdomen whilst carrying out a perineal approach together with herniorrhaphy can be performed and is, in the opinion of the authors, usually adequate; precluding the need for cystopexy or vas deferensopexy. Alternatively, cystopexy or vas deferensopexy can be performed via an abdominal approach prior to definitive herniorrhaphy.

Surgery

Castration is carried out routinely in the management of perineal hernia, as there is evidence of a reduced incidence of recurrence. The authors prefer to carry out castration in the dorsally recumbent patient prior to undertaking herniorrhaphy. There is no indication for multiple anaesthetic episodes in these cases; castration and bilateral herniorrhaphy (where indicated) should be performed at the same time.

A number of techniques have been described for the repair of perineal hernias, but the technique with the highest success rate (80–90%) is a combination of the 'conventional' or dorsal repair with transposition of the internal obturator muscle.

Perineal Hernias in Cats

Conditions reported in association with perineal hernias in cats are megacolon, perineal masses, trauma, fibrosing colitis and previously performed perineal urethrostomy. Signs include tenesmus and constipation, but unlike dogs, perineal swelling is uncommon. Cats with mild clinical signs may be able to be managed medically. Those with more severe clinical sings require surgical repair using internal obturator transposition.

Ventral Herniation and/or Sacculation of Rectum

The presence of significant ventral herniation and/or sacculation presents a considerable challenge to the surgeon. If the degree of sacculation is small, suturing the elevated obturator flaps as far medially as possible is often satisfactory, taking care to identify and avoid the urethra.

Practical tip: Place a urethral catheter preoperatively to help identify the urethra.

With larger defects, the surgeon should consider either a colopexy procedure (or transposition of the semitendinosus muscle). There are a number of case reports indicating that colopexy with cystopexy can be successful when combined with perineal hernia repair. Whether these additional procedures are performed at the time of perineal herniorrhaphy or not is based on the surgeon's preference; however, in dogs with retroflexed bladders or large rectal dilatations, performing the abdominal procedures a few days before the perineal approach often facilitates the herniorrhaphy. One report of 32 cases suggested successful treatment of perineal hernias by colopexy, cystopexy and vasopexy without definitive herniorrhaphy (Maute et al., 2001). The reported recurrence rate was 22%, which compares favourably with other reports.

Use of Prosthetic Materials

Prosthetic materials that may be used include porcine dermal collagen sheets, polyester mesh and porcine-derived small intestinal submucosa (porcine SIS). It must be remembered that biomaterials increase the risk of infection. In one series of 59 dogs in which polypropylene mesh was used, the reported infection rate was 5.6% and the recurrence rate was 12.5% (Szabo et al., 2007). In a study where porcine dermal collagen was used to treat perineal hernias in 21 dogs, the success was only 59.3% and 33% of dogs developed a serosanguineous discharge from the wound (Frankland, 1986). Porcine SIS may offer advantages over polypropylene mesh in that it promotes vascular ingrowth, is more resistant to infection and induces a regenerative response from the tissues in which it is implanted. Overall, there is a paucity of long-term follow-up in cases where prosthetic materials have been used, and thus their routine use is not currently advocated. Autogenous fascia lata grafts and the use of tunica vaginalis have also recently been reported in very small numbers of dogs.

Complications and Prognosis

The most common complication is wound dehiscence or infection at the surgical site, with a reported incidence of 6–26%. Drainage, lavage and appropriate antimicrobial therapy are usually curative.

 Faecal incontinence due to loss of external anal sphincter function may occur if the caudal rectal or internal pudendal nerves are damaged during herniorrhaphy. Function may return in cases of unilateral nerve damage due to reinnervation from the contralateral side. Bilateral nerve damage can result in permanent faecal incontinence.

 Rectal eversion/prolapse may occur immediately after surgery. Lubrication with local anaesthetic gel and gentle reduction, combined with a temporary purse-string suture (24–96 hours), are usually all that is necessary. In cases where there is prolonged tenesmus, epidural anaesthesia should be considered. Where rectal prolapse recurs, incisional colopexy should be performed to prevent further prolapse. It is also necessary to establish a cause for the tenesmus and to treat it.

 Sciatic paralysis is very rare but may occur where sutures are inadvertently placed lateral to the sacrotuberous ligament. Its presence is characterized by pain and lameness on the affected side. If noted, the sutures must be removed immediately, and this can be achieved either by revision of the original repair or via a caudolateral approach to the sciatic nerve.

 Rectocutaneous fistulae are a rare complication but may occur if the suture material inadvertently penetrates the rectal mucosa. Digital rectal examination should be carried out immediately after removing the purse-string suture. Any offending suture material should be cut per rectum.

Recurrence is uncommon when internal obturator transposition has been properly performed and is reported at between 10% and 20%. Studies have shown a significantly higher recurrence rate when herniorrhaphy is performed by an inexperienced surgeon. The most common reason for recurrence is a failure to accurately identify the anatomy of the pelvic diaphragm.

Rectocutaneous Fistulae

Rectocutaneous fistulae are a rare but potentially serious complication of any perianal surgery where there may be inadvertent penetration of the rectal lumen with a scalpel or suture materials. The clinical signs are those of dyschezia, initially with a perineal swelling. Ultimately, faeces will be seen to leak from a cutaneous wound.

The options for management include primary repair, a rectal 'pull-through' procedure, anoplasty or primary repair with omental reinforcement. The author has had some success in using the latter technique.

1.  The patient initially undergoes a laparotomy, and the omentum is lengthened as described by Ross and Pardo (1993).

2.  The omentum is placed within the pelvic canal lateral to the rectum.

3.  The laparotomy wound is closed routinely and the patient is placed in the perineal stand position.

4.  The perineal area is cleaned and the edges of the rectum are debrided as necessary.

5.  Closure of the rectal defect is achieved with simple interrupted sutures of 2 or 3 metric (3/0 or 2/0) monofilament absorbable suture material.

6.  If the pelvic diaphragm is intact, it is necessary to break down the attachment between the levator ani and the coccygeus muscles to allow access to the omentum. This is then drawn caudally into the perineal space and sutured over the rectal closure.

It is essential to close the perineal diaphragm as described above, taking care not to damage the omental vasculature.

References

1.  Frankland AL. Use of porcine dermal collagen in the repair of perineal hernia in dogs - a preliminary report. Vet Rec. 1986;119:13–14.

2.  Maute AM, Kock DA, Montovon PM. Perineal hernia in dogs - colopexy, vasopexy, cystopexy and castration as elective therapies in 32 dogs. Schweiz Arch Tierheilkd. 2001;143:360–367.

3.  Ross WE, Pardo AD. Evaluation of an omental pedicle extension technique in a dog. Vet Surg. 1993;22:37–43.

4.  Szabo S, Wilkens B, Radasch RM. Use of polypropylene mesh in addition to internal obturator transposition: a review of 59 cases (2000–2004). J Am Anim Hosp Assoc. 2007;43:136–142.