Perineal hernias result from weakening or complete failure of the muscular diaphragm of the pelvis. Although the development of hernias may be multifactorial - the predominance of intact males suggests a hormonal balance contributes to the weakening of the pelvic diaphragm. Female dogs are less frequently afflicted but, in these cases, additional measures (such as abdominal ultrasound) should be taken to rule out concurrent predisposing diseases. Successful long-term management of hernias relies upon eliminating the underlying cause (concurrent castration in most cases).
Presentation typically includes swelling adjacent to the rectum, signs of constipation, tenesmus, lethargy, stranguria (if bladder or prostate are involved) and altered tail carriage. Differential diagnoses include perianal/pelvic canal/subcutaneous masses.
Rectal examination should be performed with both left and right fingers as it is difficult to palpate on the right with the right and on the left with the left hand. Even if one side of the perianal region appears normal it should be thoroughly palpated as bilateral herniation is common. Attempts should be made to localize the bladder and prostate either within the abdomen, pelvic canal or within the hernia itself. Hydration should be carefully assessed. Diagnostic workup includes blood work and a positive contrast cystourethrogram as indicated.
Preoperative medical management can include: a low residue diet, lactulose to effect, and intermittent deobstipation. However, continued medical management will often result in worsening of the condition risking bladder entrapment and rupture or fistula development. Furthermore, chronic hernias are typically more inflamed and have a greater number of adhesions risking inaccurate tissue apposition or neurovascular damage during repair.
Surgical procedures often include castration, cystopexy and/or colopexy in addition to the definitive hernia repair. Surgery involves careful identification of the following structures; external anal sphincter, levator ani (if still present), coccygeus, internal obturator, pudendal bundle, and sacrotuberous ligament. Care should be taken to identify the exact location of the hernia (i.e., between which tissues) as this will affect how the repair is performed.
Most cases of hernia can be managed with direct apposition of the external anal sphincter to the levator ani/coccygeus dorsally and elevation of an internal obturator flap ventrally. However, additional reconstruction options include the use of the superficial gluteal, semitendinosus muscle or prosthetic implants. Repairs can be carried out with relatively large gauge monofilament sutures, either absorbable or nonabsorbable suture materials are appropriate.
Following surgical management of the hernia, a diet higher in insoluble fiber (such as diets for canine diabetes, feline hairball control or weight management) can be used to allow passage of softer bulked faeces.
Complications include potential recurrence, faecal incontinence, infection and/or contralateral herniation.