Perineal Hernia

Description

Perineal hernia is the protrusion of pelvic or abdominal viscera through the structures of the weakened or ruptured pelvic diaphragm, causing displacement of the perineal skin. The pelvic diaphragm is composed of the coccygeus, levator ani and external anal sphincter muscles and, due to its proximity to these structures, the rectum is the organ most commonly involved in perineal hernias. Perineal hernias can be unilateral or bilateral and, depending of their location, they can be further classified as dorsal, ventral, sciatic or caudal hernias. The herniated content is contained by the perineal fascia and, since the parietal peritoneum is usually intact, this constitutes a true hernial sac. The sac may contain pelvic or retroperitoneal fat, peritoneal fluid, a deviation, dilation or sacculation of the rectum, a rectal diverticulum, the prostate gland, the urinary bladder (which may be retroflexed) or the small intestine and any of these organs may become incarcerated or stangulated. In cats, the sac frequently only contains the rectum.

The cause of perineal hernia is not know but several factors have been discussed, all of which are thought to contribute to progressive weakness and atrophy of the muscles of the pelvic diaphragm. These include:

• Breed predisposition, with Welsh Corgis, Boston terriers, Boxers and Collies at particular risk.
• Sex, with females at decreased risk of developing the condition as they have stronger pelvic diaphragm muscles. In dogs, 93% cases occur in intact males but the condition is more common in neutered male cats than entire males.
• Structural weakness of the pelvic diaphragm due to prolonged tenesmus which stretches the caudal rectal nerve and produces neurogenic atrophy of the muscles of the pelvic diaphragm.
• Tail docking may reduce the size and tone of the pelvic diaphragm muscles, increasing the risk of perineal hernia. Short-tailed Corgis have a greater risk of developing the condition than those with long tails.
• Congenital or acquired myopathies, such as muscular dystrophy and myositis.
• Hormonal imbalances, particularly increases in androgens (or in androgen receptors on the pelvic diaphragm muscles) and relaxin receptors which most commonly occur in male entire dogs.
• Prostatic enlargement is not thought to be a cause of perineal hernia per se but it may contribute to the latter condition as it often produces faecal and urinary tenesmus.

Signalment

The condition is much more common in dogs than cats and, in dogs, almost all cases are described in intact males. Most cases occur in animals older than 5 years and the median age in cats and dogs is 10 years. Welsh Corgis, Boston terriers, Boxers, Pekingese and Collies are at particular risk. Females are at decreased risk of developing the condition as they have stronger pelvic diaphragm muscles. In dogs, 93% cases occur in intact males but the condition is more common in neutered male cats than entire males.

Diagnosis

There may be a history of chronic tenesmus or of another disease causing generalised muscle weakness.

Clinical Signs

Signs can be divided into physical signs related to the presence of the hernia and signs which occur when herniated organs become strangulated or obstructed. Clinical signs may therefore include:

Physical signs

• Swelling of the perineal area, either unilaterally or bilaterally.
• Caudal projection of the anus (if the hernia is bilateral).
• The rectum loses lateral support on the affected side(s) and, on digital rectal examination, the skin over the hernia can be elevated because the rectum is no longer contained within the pelvic cavity.
• Constipation/obstipation, dyschezia and tenesmus result from alterations to the normal contours of the rectum, including deviations or flexures, sacculations (unilateral dilations), bilateral dilations and pulsion diverticula. Continued tenesmus may worsen the extent of the hernia.
• Chronic tenesmus and bilateral loss of rectal support may result in rectal prolapse.

Signs due to incarceration or strangulation of organs and necessitating emergency treatment

• Stranguria or anuria due to retroflexion of the urinary bladder into the hernia.
• Vomiting due to small intestinal obstruction

Faecal incontinence occurs commonly after correction of the hernia due to disruption of the caudal rectal nerves supplying the external anal sphincter.

Laboratory Tests

Biochemistry

Parameters indicating urinary tract obstruction (as occurs with retroflexion of the bladder) may be detected, including:

• Raised serum urea, creatinine and phosphate concentrations
• Raised serum potassium concentration (not usually clinically significant until 24 hours after obstruction occurs).

Diagnostic Imaging

This is not necessarily required but radiography or ultrasonography may be useful to determine whether or not the bladder, prostate or small intestine are within the hernial sac. A positive contrast cystogram can be performed to better define the location of the bladder.

Treatment

Perineal hernias may be treated conservatively by altering the animal's diet but they are often corrected surgically.

Conservative Management

This involves the following aspects of treatment:

A diet with a high fibre content to increase the bulk and moisture content of the faeces and reduce the likelihood of constipation and faecal tenesmus.

Laxatives to increase the moisture content of the faeces. Various products are used, including lactulose, psyllium mucilloid and dioctyl sodium sulphosuccinate, a cathartic which increases the rate of secretion of fluid from the intestinal mucosa.

Actual or 'chemical' castration using delmadinone acetate, which reduces the concentration of circulating androgen hormones. Androgens and their receptors are involved in the aetiopathogenesis of perineal hernia and castration will also prevent most prostatic diseases (with the exception of prostatic neoplasia).

Occasional enemas or manual evacuation of faeces can be performed to relieve any constipation and to remove any faeces that have become impacted in rectal sacculations or diverticula.

Surgical Management

Surgical Techniques

Surgical intervention is indicated if medical treatment has failed or if herniated organs become incarcerated or strangulated. Two major techniques have been described to achieve herniorraphy:

An internal obturator transposition herniorraphy is most commonly performed with the animal positioned in sternal recumbency with extended hips (as for surgery of the anus, anal sacs or vulva). An incision is made dorsoventrally, parallel to the median plane on the affected side and the hernial sac is identified and entered. The herniated organs are identified and their viability is assessed before they are returned to the abdominal or pelvic cavity. The incision is extended to reveal the internal obturator muscle which originates on the dorsal surface of the ischiatic table and runs over the lesser sciatic notch to insert on the greater trochanter of the femur. The muscle is mobilised from the ischium using a periosteal elevator, moved dorsally and sutures are then passed between it, the coccygeus and levator ani muscles and the external anal sphincter. The sutures should be pre-placed before they are tied and care should be taken to ensure that they do not penetrate through to the rectal lumen. The tendon of the internal obturator may be sectioned to enable the muscle to be transposed but care should be taken not to damage the sciatic nerve which runs beside it over the sciatic notch. The procedure can be performed bilaterally but, since it increases the degree of faecal tenesmus, an interval of 4-6 weeks is often intermitted before the contralateral repair is completed.

The traditional herniorraphy is a simpler version of the above technique, in which sutures are placed between the external anal sphincter, coccygeus and levator ani without elevating the internal obturator muscle. Since the internal obturator is not used to fill space created by the hernia, the sutures placed in this technique are usually under greater tension and they may cause deformity of the anus.

Castration should be undertaken at the same time as this reduces the risk of recurrence of 2.7 times.

Other procedures may be performed to prevent abdominal organs from moving into the hernia, including a ductus deferopexy where the bladder is tethered to the ventral abdominal wall by the transected ducta deferentia and a colopexy where the descending colon is attached to the left body wall, preventing rectal prolapses and severe rectal dilations.

Post-operative complications

The following phenomena may be observed post-operatively:

• Tenesmus may worsen in the immediate post-operative period, especially if the anus has been deformed by the herniorraphy and this may even lead to rectal prolapse. The condition can be managed by softening the faeces (as described above) and placing an anal purse-string suture in the event of rectal prolapse.
• Neuropraxia of the sciatic or caudal rectal nerves may occur. The caudal rectal nerves are most often damaged as they run along the dorsal surface of the internal obturator muscles, lateral to the coccygeus and levator ani. Damage to the nerves results in temporary or permanent faecal incontinence. If there are signs of sciatic nerve paralysis, the offending sutures must be removed immediately.
• Urinary incontinence may occur if the bladder is retroflexed and its nervous supply damaged.
• Surgical wound infections may occur, especially if any sutures have penetrated the rectal lumen.

Prognosis

The rate of recurrence is around 15% one year after surgical herniorraphy. Cases involving bladder retroflexion have the poorest prognosis and, although cases managed medically may have an acceptable quality of life, there is always a danger that the bladder or another organ will be incarcerated and strangulated in the hernial sac.

References

• Fossum TW (1997) Small Animal Surgery Mosby
• Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company.
• Hall, E.J, Simpson, J.W. and Williams, D.A. (2005) BSAVA Manual of Canine and Feline Gastroenterology (2nd Edition) BSAVA
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.