Key Points

 Knowledge of anatomy of pelvic diaphragm is essential

 Clearly identify anatomic structures to be sutured

 Examine hernia closure carefully for defects

 After surgery remove pursestring, palpate rectum, watch patient walk back to cage

Applied Anatomy

Perineal hernia is defined as a defect in the anatomic structures making up the pelvic diaphragm. The pelvic diaphragm is made up of levator ani muscle, coccygeus muscle, external anal sphincter muscle, and perineal fascia. Other important anatomic structures that aid in surgical repair of perineal hernia include the sacrotuberous ligament and internal obturator muscle.

Perineal hernia occurs when protrusion of pelvic viscera (i.e., prostate, paraprostatic fat, rectum) or abdominal viscera (i.e., bladder, small intestine) occurs through supporting structures making up the pelvic diaphragm.

Etiology

The cause of perineal hernia is unknown. Many factors have been incriminated in its etiopathogenesis including:

1.  hormonal imbalance

2.  congenital predisposition

3.  structural weakness of the pelvic diaphragm

4.  prostatic disease

5.  chronic constipation

It was shown in one study of 771 dogs that 93% of affected dogs were intact males. It has also been shown that females have a larger, heavier, stronger levator ani muscle with a longer rectal attachment than the male, and that the sacrotuberous ligament in the female is larger. These findings may help support a hormonal influence to the etiology.

Certain breeds such as Boston terrier, Pekinese, and boxers have a predisposition for perineal hernia, suggesting a familial risk. However, many mixed breed dogs also are commonly affected.

Structural weakness of the pelvic diaphragm, especially in breeds with rudimentary tails (e.g., Boston terrier, Old English sheepdog, boxer) may imply a conformational predisposition. However, breeds with normal tails (e.g., German shepherd dog, collie, mixed breeds) have an equally high incidence.

Prostatic disease is commonly seen in older (> 6 yrs of age) intact males. This may cause severe straining and predispose the patient to perineal hernia formation. However, many dogs that present with perineal hernia do not have significant prostatic disease.

Any disorder resulting in chronic straining to defecate may have an influence on the incidence of perineal hernia in the dog.

Diagnosis

A diagnosis of perineal hernia can be made on history, clinical signs, and visual and digital rectal examination. Dogs often present with a history of constipation and tenesmus. Visual perineal examination reveals perineal swelling that may be reducible. Digital rectal examination reveals loss of the normal pelvic diaphragm and either abdominal viscera or pelvic viscera within the hernial sac.

Occasionally patients present with urinary obstruction due to retroflexion of the urinary bladder into the hernial sac. A presumptive diagnosis is based on history of urinary obstruction, perineal swelling that is firm and turgid on palpation, and presence of a fluctuant mass in the perineum on rectal palpation. Definitive diagnosis is accomplished by either urethral catheterization resulting in reduction of the size of the mass or centesis of urine from the perineal mass. These patients may be quite sick depending on the duration of urinary obstruction. An indwelling urinary catheter and sterile collection device should be placed while the patient's renal function and other metabolic derangements are stabilized.

Rarely, a patient will present with incarcerated small intestine. Emergency reduction via abdominal exploratory is indicated. Resection and anastomosis is performed based on bowel viability after reduction and enteropexy considered. Repair of the perineal hernia should be staged depending upon patient status.

Surgical Treatment

Treatment of perineal hernia by surgical correction is generally accepted by most clinicians as the most successful means of management. Medical management with stool softeners and periodic digital evacuation may be attempted but may only temporarily control the problem.

Preoperative preparation of the patient includes fasting the day before surgery, preoperative antibiotics and proper laboratory evaluation (i.e., BUN, CBC, UA). Enemas have been suggested the day before surgery. This author does not recommend enemas due to the liquid feces presented to the anal orifice at the time of surgery. Instead, digital evacuation of the rectum on the day of surgery after the patient has been anesthetized is recommended. After complete rectal evacuation, the patient is placed in dorsal recumbency and castrated. The patient is then placed in perineal position, a tampon placed in the rectum, and a pursestring suture placed in the anal orifice. Alternatively, the patient may be castrated from a perineal approach, eliminating the need for repositioning.

A curved incision over the perineal mass is made from the tail base to a point midway between the pubis and ischial tuberosity then returning to the midline proximal to the scrotum.

The hernial sac is entered and the contents either reduced (i.e., prostate, small intestine, bladder) or removed (i.e., paraprostatic fat, prostatic cysts).

The following anatomic structures are located:

 External anal sphincter muscle

 Levator ani muscle (often difficult to see and sometimes nonexistent)

 Coccygeus muscle

 Pudendal artery and vein perineal nerve

 Sacrotuberous ligament internal obturator muscle

After proper orientation and location of the above anatomic structures, the caudal lateral aspect of the internal obturator muscle is incised and elevated from the ischium. It is elevated to the caudal aspect of the obturator foramen and reflected dorsally. Its tendon of insertion may be left intact (small dogs) or incised (large dogs) depending upon how much dorsal elevation is necessary to close the defect.

Interrupted sutures are preplaced from dorsal to ventral beginning with the coccygeus muscle and suturing it to the external anal sphincter. As suturing progresses ventrally, the internal obturator m. is sutured to the coccygeus m. The ventral aspect of the hernia is closed by suturing the internal obturator muscle to the external anal sphincter m. After all sutures have been properly placed, each is tied separately from dorsal to ventral.

Absorbable or nonabsorbable suture material has been used successfully in perineal hernia repair. This author recommends synthetic absorbable monofilament suture (i.e., PDS, Maxon).

Rarely, a prostatic abscess is found in the hernial sac. If this occurs, the surgeon can reduce the abscess into the abdominal cavity, repair the hernia, then explore the abdomen via ventral midline celiotomy and manage the abscess (i.e., drainage, omentalization, marsupialization, or excision). Another option is to provide tube drainage via the perineal approach. The advantage of using the perineal approach is only one major procedure needs to be done; the disadvantage is the difficulty in obtaining proper ventral drainage.

If a rectal diverticulum or sacculation is present in the hernial sac, the option for reduction or excision of the diverticulum or sacculation and hernial repair exists.

It has been recommended by several authors that because of the straining caused by the presence of sacculations or diverticula, that they be excised by cross-clamping, excision and suturing with a double layer, continuous inverting suture technique. The hernia is then repaired as described.

It is the authors' opinion that most rectal abnormalities involve rectal deviation (not diverticula or sacculation); reduction of the rectal deviation and perineal hernia repair is the treatment of choice.

After properly placing and securing all sutures used to repair the hernial defect, subcutaneous tissues and skin are closed with simple interrupted sutures. The subcutaneous tissues are generally closed with an absorbable suture and the skin with a nonabsorbable suture of the surgeon's choice.

Immediately postoperatively, the pursestring suture is removed, the rectum palpated for sutures that may have inadvertently been placed through the rectal wall, and the patient watched until it can ambulate to its cage.

If a strand of suture material can be palpated in the rectal lumen, it is cut via a rectal approach. If the suture is left in place, a rectocutaneous fistula may develop. If more than one suture has penetrated into the rectal lumen, the hernial repair should be redone.

If the patient cannot ambulate on its hind leg or exhibits severe hind leg pain (i.e., ipsilateral to the side of hernial repair) and the sacrotuberous ligament was utilized in the closure, it is likely one of the sutures placed around the sacrotuberous ligament has entrapped the sciatic nerve. When using the sacrotuberous ligament in hernial repair, care should be taken to use its leading edge instead of encircling it as the close proximity of the sacrotuberous ligament and sciatic nerve may result in sciatic nerve entrapment. If the surgeon suspects sciatic nerve entrapment the patient should be immediately anesthetized, the hernial repair re-explored, sutures placed around the sacrotuberous removed, and the hernia re-repaired using the leading edge of the sacrotuberous ligament. Alternatively, the sciatic nerve can be explored and the entrapping sutures identified and cut.

Postoperative management includes systemic antibiotics for seven days, low residue diet, an Elizabethan collar and suture removal in 10-14 days.

Postoperative complications include:

1.  wound infection

2.  fecal incontinence

3.  sciatic nerve entrapment

4.  excessive straining due to postsurgical pain

5.  bladder atony producing anuria

6.  rectal prolapse

7.  rectocutaneous fistula

Cystopexy/Colopexy

Surgical management of perineal hernia typically involves reconstruction of the pelvic diaphragm by anatomic muscle apposition of transposition of regional muscle flaps. Cystopexy, fixation of the deferent ducts, and colopexy have been described as adjuncts to herniorrhaphy when urinary bladder retroflexion or rectal prolapse accompany herniation. The reported rate of recurrence of hernias or clinical signs after herniorrhaphy is 10 to 46%; the overall complication rate is 28-61%. Repairing large, chronic, or recurrent hernias can be especially challenging. For these cases, cystopexy and colopexy may provide a simpler technique with lower morbidity as an alternative to herniorrhaphy.

Materials and methods: Dogs were identified in which large or recurrent perineal hernias had been managed with cystopexy and colopexy (CC), Patient evaluations were performed by phone interview with owners and /or examination at the hospital where surgery was performed.

Results: Nine male dogs were evaluated (median age 9 years; range 5.5 to 11.2). All were neutered (previously or at the time of CC). Five dogs had 1 to 4 prior failed herniorrhaphies and 4 had no prior hernia surgery. Median follow up was 9 months (range 2 to 24). All dogs had tenesmus as a complaint; signs improved or resolved in 4 of 9 dogs after CC. Stranguria was a complaint in 6 of 7 dogs with urinary bladder retroflexion;' signs improved or resolved in 5 of these 6 dogs after CC. Rectal prolapse was a problem in 2 dogs: it resolved in both dogs after CC. One dog had fecal and urinary incontinence prior to CC; signs were unchanged postoperatively. Complications encountered in 1 dog (persistent tenesmus and partial avulsion of the cystopexy resulting in uroabdomen) were attributed to technical error. Surgical complications were not observed in the other 8 dogs.

Conclusion: Cystopexy and colopexy may be of limited value as a sole surgical treatment for dogs with large of recurrent perineal hernias. Though CC may effectively resolve rectal prolapse and reduce signs of stranguria secondary to bladder retroflexion, tenesmus was unimproved in 5 of 9 patients evaluated.