THE MERCK VETERINARY MANUAL
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Perineal Hernia

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Perineal hernia is a lateral protrusion of a peritoneally lined hernial sac between the levator ani and either the external anal sphincter muscle or the coccygeus muscle. Incidence in intact 6- to 8-yr-old male dogs is disproportionately high, and Welsh Corgis, Boston Terriers, Boxers, Collies, Kelpies and Kelpie crosses, Dachshunds and Dachshund crosses, Old English Sheepdogs, and Pekingese are at higher risk.

Many factors are involved, including breed predisposition, hormonal imbalance, prostatic disease, chronic constipation, and weakness of the pelvic diaphragm due to chronic straining. The higher incidence among sexually intact males is evidence that hormonal influences probably play a primary role. Prostatic hypertrophy attributed to sex-hormone imbalance has been strongly implicated. Both estrogens and androgens have been cited as causative agents.

Common signs include constipation and obstipation, tenesmus, and dyschezia. Stranguria and urinary obstruction may develop secondary to retroflexion of the bladder and prostate. Visceral strangulation may be seen. A perineal swelling ventrolateral to the anus is evident. Herniation may be bilateral, but two-thirds are unilateral and >80% of these are on the right side.

The mass is soft and fluctuant and may be reduced digitally. A firm, painful swelling may be compatible with retropulsion of the bladder and prostate. Determination of contents is often made by rectal examination and perineal centesis (to determine whether urine is present). More than 90% of perineal hernias contain a rectal deviation, which is a sacculation of the rectum into the hernial sac, where the layers of the rectal wall remain intact.

Perineal hernia is rarely an emergency, except when the bladder has strangulated and the animal is unable to urinate. If catheterization cannot be done, the urine should be removed by cystocentesis and an attempt made to reduce the hernia. An indwelling urinary catheter may be necessary to ensure urethral patency and prevent recurrence of obstruction.

Surgical correction is always indicated, and concurrent castration to reduce recurrence is recommended. The prognosis is guarded because of the high incidence of recurrence (10%–46%) and postoperative complications such as infection, rectocutaneous fistula, anal sac fistula, ischiatic and pudendal nerve entrapment, and rectal prolapse.

Last full review/revision December 2013 by Stanley I. Rubin, DVM, MS, DACVIM

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