The definition of hernia says it must contain a peritoneal lining to be a valid one, and there is no apparent serosal lining in the hernia we are going to discuss. According to the definition, we suggest to change this wrongly named Perineal "hernia" to Rupture of the Pelvic Diaphragm (RPD). Goals of performing a RPD repair include achieving adequate exposure, accurate knowledge of the anatomy of the perineal region, avoiding injury to vital structures, primarily use the patients own tissues for repair and minimizing postoperative complications. The underlying cause of this surgical pathology is poorly understood. RPD develops when a weakness and/or separation of the muscles and fascia of the pelvic diaphragm allow a caudal displacement of some of the abdominal and/or pelvic organs and fat. This might be accompanied by deviation, sacculation or diverticulum's formation of the rectum. The herniation typically occurs between the external anal sphincter medially, the levator ani and coccigeus muscles dorsolaterally, the sacrotuberous ligament laterally and the obturator muscle ventrally.

Clinical presentation

The condition predominates among middle aged to older (7-9 years), non castrated (95%) male dogs (97%). Very rarely in female dogs and cats, even though there is description of 40 cases in cats (Welches et al, 1992)plus five other descriptions. Two thirds are unilateral and the right side is the most commonly affected. Among the breeds frequently affected in Argentina we can mention German shepherd, Boxer, Doberman, Pekingese, Dachshund and Mongrel dogs.

Along with the causes mentioned are hormonal imbalance, prostatic disease, constipation and tenesmus, and muscular atrophy. Retroflexion of the bladder constitutes an emergency situation and prompt catheterization and decompression are indicated. If catheterization is not possible cystocentesis is mandatory followed by reposition of the bladder. In cats more frequently megacolon, perineal urethrostomy and perineal masses (generally adenocarcinoma of the anal sacs) are the identified causes of RPD. Female cats are more prone to suffer the pathology compared to dogs. As another contrast the domestic shorthair is the breed most commonly affected. History, clinical signs and physical examination including rectal palpation of the pelvic diaphragm make definitive diagnosis. Radiographs and ultrasound can be indicated for academic purposes and to finally assess what kind of abnormality is presented by the rectum due to impaction of fecal material against the debilitated rectal walls and which are the organs "luxated" at the time of herniation. The RPD can be classified as dorsal when the luxated viscera passes between the coccigeal and levator ani muscles. Most commonly caudal or medial when the presentation is between the external anal sphincter, levator ani and internal obturator muscles. Ventral between the ischiocavernosus, ischiourethralis and bulbocavernosus muscles and sciatic or lateral involving the sacrotuberous ligament and the coccigeal muscle. Dietary management, associated with laxatives or enemas can be instaurated to prepare the patient for surgery. The latter should not be used beyond 12-18 hours before surgery in order to avoid a soiled surgical field.

Before initiating the surgical procedure a final rectal examination must be done, to reassess the pathology and to evacuate any fecal remnants within the rectum. Anal sacs should be emptied and a purse-string suture placed around the anus. If enemas have been used short before surgery a gauze tampon can be placed to prevent any soiling of the surgical field from the watery feces. After anesthesia induction, clipping and prepping the perineal region or the proximal and caudo-lateral aspect of the proximal hindquarters is carried out, The patient is placed in sternal or lateral recumbency according to the approach chosen.

Caudal approach: With the patient in sternal recumbency on a padded surface and with the surgery table slightly in Trendelemburg position, a lateral incision is made from the base of the tail to just distal the medial aspect of the ischial tuberosity. The incision is carried out through the subcutaneous layer. The perineal fascia is bluntly dissected and is reflected laterally and medially to be anchored with towel clamps to the barrier drapes. The hernial sac is opened and the content inspected. Uneven amounts of straw like fluid can be aspirated from the sac. Many times necrosed fat can be found as well as an entrapped prostate gland or bladder or intestine. Prostate biopsy can be performed before reducing the herniated organ. Accurately recognize the muscular and neuro vascular structures in the area. Internal pudendal vessels and nerve running over, and slightly medial to the dorsal aspect of the internal obturator muscle are thoroughly identified. Muscles and ligaments to be used in the RPD repair are also identified. It is important to remember that cats do not have sacrotuberous ligament and both anal sphincters are striated. Suture material selection will depend on the surgeon's choice and expertise. We like to use monofilament nylon or polypropylene or PDS^®, Maxon^® or Monocryl^® depending on how severe the rupture was. Sizes will vary with the size of the patient. Generally speaking sizes between 3/0 and 2/0 are the most frequently used. Sutures must be preplaced to assess their position and to improve visualization of the defect while repairing it.

Lateral approach: With the patient in lateral recumbency and the affected side upward, the upper hindquarter is displaced cranially and tied in extension. The lower leg is displaced caudally until a 90-degree angle is formed between both legs. The patients tail is displaced dorsally. Surgical landmarks are tuber coxae, greater trochanter, ischial tuberosity, base of the tail, anus and ischial arch. An incision, slightly curved, from the tuber coxae to a midpoint between the anus and the ischial tuberosity is made with the scalpel. The subcutaneous layer is bluntly dissected and the superficial perineal fascia is sectioned over the hernial sac. The prolapsed organs are returned to the pelvic cavity. The ischial arch is palpated and the adipose tissue is bluntly separated from the caudal edge of the internal obturator muscle clearing it out. Once the dissection is finished the pudendal vessels and nerve as well as the caudal rectal nerve and artery must be identified and assessed for any damage. The dissection is continued from the ischial tuberosity up to the sacrotuberous ligament, over the coccigeal muscle, ventrally to the base of the tail. Finally the external anal sphincter is located and his upper surface cleared. A new perpendicular skin incision can be added to reach the insertion of the superficial gluteal muscle starting half way from the previous one and extending distally 1-2 cm. beyond the greater trochanter. When the levator ani can not be used for the repair muscular flaps from the internal obturator and superficial gluteal muscles can be created. Insertion tendons from both muscles are severed and the muscle flaps are displaced and anchored to the remaining muscles to close the perineal defect. Always catheterize the urethra to help identify its location when sutures are preplaced.

The classical technique for closure of the RPD can be obtained in detail from most surgery textbooks. After all stitches are tied, the perineal fascia is sutured on top of the underlying layer in a single continuous pattern. This will add extra strength to the muscular stratum and act as a relief layer, allowing for a better healing under no excessive tension on the area. Subcutaneous and skin layers are sutured in a routine fashion. Redundant skin can be trimmed away and if dead space remains Penrose drains are indicated. The generalized use of the internal obturator muscle flap technique has reduced recurrence problems, although potential urethral damage must be taken under consideration. Other techniques include semitendinous muscle transposition, use of Marlex® mesh, and colopexy and cystopexy by deferent duct fixation as adjuvant techniques to prevent recurrences. It must be remembered to take biopsies of the tissues that look abnormal in the ruptured place (prostate, masses). Most textbooks recommend not "touching" a flexure, sacculation or diverticulum present in place since they tend to solve once the RPD has been repaired. Sutures must be placed through, not around, the sacrotuberous ligament. This may demand a glove change since they can be pierced during palpation of the needle passing through the ligament. This is the strongest point for anchoring and can slightly distort the appearance of the perineal area.

Castrated dogs do not tend to develop RPD and non-castrated dogs have a recurrence rate 2.7 times higher. Castration will also reduce the development of other prostatic diseases and is the generalized surgical treatment of choice for benign prostatic hypertrophy. It will be the surgeons' choice to do a scrotal or a prescrotal castration. Perioperative antibiotics are indicated. After surgery is finished, do not forget to remove the purse string suture around the anus and palpate rectally the repair to have a primary assessment of the job done.

Complications can occur and will depend on the surgeon's skills, experience and understanding of the "disease." This is the reason why recurrence rate varies between 10 to 46 %.

Sciatic nerve entrapment occurs when sutures are placed around the sacrotuberous ligament. A caudolateral hip approach must be used to correct the problem. Any other approach can be time consuming and will add extra damage to the nerve because of the delay to release it as soon as possible. Other nerve injuries include pudendal nerve or rectal caudal nerve incorporation into the repair when sutures are preplaced through the muscles used in the RPD repair. This may result in temporary or permanent fecal incontinence (less than 10%). Erroneous suture placement through the rectum or anal sacs can lead to infection or abscessation of the area (6.4-26%). A rectal prolapse (2-6%) can be a minor postop problem when doing a bilateral repair. This condition usually improves in a couple of days after placing a not to tight purse string suture around the anus. Otherwise a resection of the redundant prolapsed mucosa must be performed.

Discussion

It is important to remark that the lateral approach does not replace the perineal approach because it is more effective. Both approaches handled with a stand out technique have a similar level of therapeutic success. The election of the lateral approach must not be made in order to obtain a greater success rate but rather for a simple matter of convenience to the surgeon while reconstructing the pelvic diaphragm. For older patients with increased surgical risk the lateral approach can be more suitable because this position will avoid the potential anesthetic complications that may occur in sternal recumbency with the head in a lower position. The increased weight of the abdominal viscera over the diaphragm may reduce the pulmonary ventilation, cardiac output and arterial pressure. Many times older patients must be on positive pressure ventilation to protect their respiration. Small unilateral ruptures, with little or no content are a good indication for the perineal approach. Minimal tissue damage, no muscular flap transposition and fewer complications in the postop. Large, older ruptures are a good indication for the lateral approach because two muscle flaps can be created to attain a strong repair of the defect. The lateral approach allows for a better visualization of the regional anatomy thus avoiding a sometimes-blindfolded suture placement. The surgeon can get a good approach and transposition of the muscles reducing suture tension. Transposition of the semitendinous muscle can be considered for the repair of bilateral ruptures where the ventral aspect of then perineum is severely affected.

Postoperative management

Analgesia and pain control are provided intra and postoperatively to manage a smooth recovery from surgery. Low residue diet and stool softeners are indicated to minimize stress on the repaired perineum and allow for a better healing. E collars or neck braces will be added as needed to prevent auto mutilation of the patient.