Perineal hernia occurs when pelvic diaphragm muscles fail to support the rectal wall, allowing persistent rectal distention and impaired defecation. Pelvic and or abdominal contents herniate into the deviation.
The cause of pelvic diaphragm weakening is poorly understood, but is believed to be associated with male hormones, straining, and congenital or acquired muscle weakness or atrophy. The pelvic diaphragm is stronger in female dogs than in males. Atrophy of the pelvic diaphragm muscles, possibly of neurologic origin, has been identified in some animals with hernias.
Conditions That Cause Straining and May Predispose to Perineal Herniation
Herniation may be unilateral or bilateral. Most herniations occur between the levatorani, external anal sphincter, and internal obturator muscles (caudal hernia); however, some occur between the sacrotuberous ligament and coccygeus muscle (sciatic hernia), levatorani and coccygeus muscles (dorsal hernia), or ischiourethralis, bulbocavernosus, and ischiocavernosus muscles (ventral hernia).
Hernial contents are surrounded by a thin layer of perineal fascia (hernial sac), subcutaneous tissue, and skin. The hernial sac may contain pelvic or retroperitoneal fat, serous fluid, a deviated or dilated rectum, a rectal diverticulum, prostate, urinary bladder, or small intestine.
Cats usually have only rectum within the hernial sac.
Organs displaced into the hernia may become obstructed and strangulated. Visceral obstruction or strangulation is associated with rapid deterioration unless the obstruction or entrapment is corrected
Clinical signs may include perineal swelling, constipation, obstipation, dyschezia, tenesmus, rectal prolapse, stranguria, anuria, vomiting, flatulence, and/or fecal incontinence.
Physical Examination Findings
Differential diagnoses for perianal swelling include perineal hernia, perianal neoplasia, perianal gland hyperplasia, anal sacculitis, anal sac neoplasia, atresia ani, and vaginal tumors.
Differential diagnoses for dyschezia include rectal foreign body, perineal hernia, perianal fistula, anal stricture, rectal stricture, anal sac abscess, rectal neoplasia, anal neoplasia, anal trauma, anal dermatitis, rectal pythiosis, and anorectal prolapse.
The goal of treatment is to relieve and prevent constipation, dysuria, and organ strangulation. Causative factors (i.e., urinary tract obstruction or infection, megacolon, and prostatitis) should be corrected. Normal defecation sometimes can be maintained using laxatives, stool softeners, dietary changes, periodic enemas, and/or manual rectal evacuation. The urinary bladder can be decompressed by centesis or catheterization.
However, long-term use of these treatments is contraindicated because life-threatening visceral entrapment and strangulation may occur.
Herniorrhaphy should always be recommended. Retroflexion of the urinary bladder and visceral entrapment require emergency surgery. Castration is recommended during herniorrhaphy because it has been reported to reduce recurrence. Non-castrated dogs have a recurrence rate 2.7 times greater than castrated dogs.
The two most commonly used surgical techniques:
1. The traditional, or anatomic re-apposition
2. The internal obturator roll-up, or transposition technique. It is more difficult to close the ventral aspect of the hernia using the traditional technique.
Bilateral herniorrhaphy is possible, but postoperative discomfort and tenesmus may be greater than after unilateral procedures.
Colopexy may help prevent recurrent rectal prolapse after herniorrhaphy.
Fixation of the ductus deferens may help prevent recurrence when the bladder or prostate has been displaced into perineal hernias.
Cystopexy has also been performed, but is not routinely recommended as retention cystitis may occur.
Postoperative tenesmus and rectal prolapse may be more common in these cases. The internal obturator transposition technique is more difficult, especially if internal obturator muscle atrophy is severe. However, it causes less tension on sutures and less deformity of the anus, and creates a ventral patch or sling for the defect.
Stool softeners should be given 2 to 3 days before surgery. The large intestine should be evacuated with laxatives, cathartics, enemas, and manual extraction. Prophylactic antibiotics effective against gram-negative and anaerobic organisms should be given intravenously after induction of anesthesia. If the urinary bladder is retroflexed into the hernia, a urinary catheter should be placed or cystocentesis performed via the perineum to relieve distress and prevent further physiologic deterioration.
Clip and aseptically prepare the perineum for surgery. The prepared area should extend 10 to 15 cm cranial to the tail base, laterally beyond the ischial tuberosity, and ventrally to include the scrotum.
The animal should be positioned in ventral recumbency with the tail fixed over the back, the pelvis elevated, and the hind legs padded.
Make a curvilinear incision beginning cranial to the coccygeus muscles, curving over the hernial bulge 1 to 2 cm lateral to the anus, and extending 2 to 3 cm ventral to the pelvic floor). Incise the subcutaneous tissue and hernial sac. Identify and reduce the hernial contents by dissecting subcutaneous and fibrous attachments. Biopsy any abnormal structures within the hernia (e.g., prostate and masses). Maintain hernial reduction by packing the defect with a moistened, tagged sponge. Identify the muscles involved in the hernia, the internal pudendal artery and vein, the pudendal nerve, the caudal rectal vessels and nerve, and the sacrotuberous ligament. Repair the hernia with one of the described techniques. After herniorrhaphy, perform a caudal castration through a median perineal incision
1. Traditional (Anatomic) Herniorrhaphy
Preplace simple interrupted 0 or 2-0 monofilament sutures using a large, curved needle Begin suture placement between the external anal sphincter and the levatorani, coccygeus, or both muscles. Space sutures less than 1 cm apart. As placement progresses ventrally and laterally, incorporate the
sacrotuberous ligament for a secure repair if necessary.
Figure-1: Perineal hernia repair using the traditional technique
2. Internal Obturator Transposition Herniorrhaphy
Incise the fascia and periosteum along the caudal border of the ischium and origin of the internal obturator muscle. Using a periosteal elevator, elevate the periosteum and internal obturator muscle from the ischium Transpose dorsomedially or roll up the muscle into the defect to allow apposition between the coccygeus, levatorani, and external anal sphincter. Transect the internal obturator tendon of insertion, if necessary, to get adequate coverage of the defect. The internal obturator tendon often is difficult to visualize, making transection difficult. Take care to prevent transection of the caudal gluteal vessels and perineal nerve. Preplace simple interrupted sutures the same as with the traditional technique. Begin by apposing the combined levatorani and coccygeus muscles with the external anal sphincter muscle dorsally. Then place sutures between the internal obturator and external anal sphincter medially and the levatorani and coccygeus muscles laterally.
Fig 2: Internal Obturator transposition technique
POSTOPERATIVE CARE AND ASSESSMENT
Post-Operative Perineal Hernia Repair
Possible Complications of Perineal Herniorrhaphy
Most postoperative complications can be prevented by meticulous surgical technique. Hernia recurrence or contralateral herniation is believed to be reduced by castration during herniorrhaphy
Recurrence is related to the expertise of the surgeon; inexperienced surgeons have higher recurrence rates. Infection and dehiscence usually can be prevented by appropriate antibiotic prophylaxis & surgical technique.