Hernias

Definition and Etiology

An incisional hernia results from disruption of an abdominal wall closure. Acute incisional hernias generally develop within the first 5-7 days after surgery, whereas chronic hernias are seen weeks to years postoperatively.¹ Incisional hernia incidence is reported to be between 0.2 and 5% in humans and up to 16% in large animals depending on the surgical approach to the abdomen, certain predisposing factors, and overall patient status.^2,3,4 Incisional herniation in small animals is uncommon averaging less than 1% of abdominal closures in two large retrospective studies.^5,6

Predisposing causes for acute and chronic incisional hernia vary and are interrelated. Reported risk factors for acute incisional hernia include increased intra-abdominal pressure from pain, entrapped fat between hernia edges, inappropriate suture material use, infection, long-term steroid treatment, and poor postoperative care.⁷ Technical error in surgery, however, is felt to be the most common cause of acute wound disruption.^8,9 Factors associated with chronic incisional hernia in humans include: obesity, hypoproteinemia, cardiopulmonary complications, abdominal distention, skin wound dehiscence, and deep fascial infection. Local wound complications, especially deep infection, appear to be the most important predisposing cause of chronic incisional hernias.^10,11

Incisional hernias result from either excessive forces acting on the abdominal incision or poor holding strength of the sutured wound. Forces acting to disrupt the abdominal incision are mainly derived from excessive intraabdominal pressure or muscle tension. Increased intra-abdominal pressure is observed in such conditions as obesity, abdominal effusions, pregnancy, or organ distension from ileus or obstruction; all these problems dramatically increase incisional hernia risk.^10,11 Poor control of postoperative pain, or uncontrolled exercise early in the postoperative period, increases the risk of wound breakdown due to excess force on abdominal wound edges.

The choice of suture material used for abdominal closure is rarely the sole cause of incisional hernia, provided the appropriate size is used.^8,12 However, choice of suture type may be critical in patients that have prolonged wound healing or are severely catabolic and when wound infection is present, particularly when an unpredictable, rapidly absorbable suture such as chromic gut is used.⁸ Inappropriate knot tying technique or inadequate number of throws for suture knots in an abdominal wall closure increases the risk of herniation.¹³ If a continuous pattern is selected for closure it is critical that the suture strand not be kinked, clamped, or knotted, all of which drastically reduce suture strength.⁵ The only hernia found in one retrospective study of incisional hernias was due to a broken suture strand in a continuous abdominal wall closure.⁵ Consequently, many surgeons choose one size larger suture when closing the abdominal wall with continuous patterns since the entire wall closure could disrupt from breakage of the single suture line.⁶

Whether suture is placed in an interrupted or continuous pattern, or the abdomen is closed in a single or double layer has little significance in incisional hernia formation provided the strength holding layer is incorporated.^5,6,12,13 Knotted interrupted sutures have a lower breaking strength than when unknotted. More shear forces are activated in the simple interrupted pattern than in the continuous pattern when tension is applied to the wound. Tension along the entire suture line becomes equally distributed when using a continuous pattern particularly when appropriate suture spacing is utilized.⁵ A suture length to wound length ratio of 4:1 for laparotomy closure has proven in human clinical studies to reduce hernia incidence.¹⁴ However, interrupted suture patterns in abdominal wall closure may be safer to use if wound edges have questionable viability or strength.¹ Excess intrinsic or extrinsic suture tension leads to significantly weaker abdominal closures, so sutures should be placed to appose, not crush, fascia.¹⁴

The most common cause of incisional hernia in small animals is failure to place sutures in the strength holding layer of the abdomen, with appropriately sized tissue bites.^1,6,8 Successful lasting abdominal wall closures must include the external rectus fascia (the main strength holding layer of the abdominal wall).⁵ Sometimes the subcutaneous tissue or suspensory fascia of the prepuce overlying the external rectus fascia is mistakenly incorporated in the abdominal closure, causing incisional hernia. In other instances, sutures do not include at least 0.5 cm of fascia rendering the wound susceptible to breakdown with even minor wound tension.¹ Closure of the internal rectus fascia (including peritoneum) with the external fascia not only prolongs the procedure time and increases trauma from tissue manipulation, but may also increase postoperative pain.^5,15,16 In addition, suture material penetrating the peritoneum is a known potent stimulus for adhesion formation.^5,16 Even without suturing, the peritoneum rapidly covers and seals exposed muscle within several days. Furthermore, the peritoneum is a rather delicate membrane, so it does not offer appreciable strength when included in the abdominal closure. Thus, inclusion of internal rectus fascia or peritoneum in abdominal closure is not required or recommended to ensure successful abdominal repair.^5,15

Clinical Signs and Diagnosis

Signs of acute incisional herniation usually develop within the first three to five days after surgery.⁸ Wound edema and inflammation are signals of altered wound healing from any cause, and these signs may be seen early in the sequence of events leading to herniation. Serosanguineous drainage from the incision and swelling are important and consistent signs of impending acute abdominal wound dehiscence across animal species.^4,17 Swelling is usually soft and painless unless infection or organ compromise is present. Incisional drainage often occurs from a benign problem after surgery such as a seroma, however, this condition must be differentiated from those patients with acute incisional hernia. Early diagnosis and treatment of incisional hernias are vital to reduce the possibility of complete wound dehiscence and evisceration (organ protrusion).¹

Any wound exhibiting signs of altered wound healing (edema, swelling, inflammation) should be examined carefully for incisional herniation.¹ Seroma, hematoma, cellulitis, or excessive foreign body response to buried suture material are differential diagnoses for acute incisional hernias. The skin incision line should be manipulated laterally during deep palpation over the muscle wall closure to aid in definition of the abdominal suture line. Further diagnostic testing (radiography, ultrasound, and fine needle aspiration) may be required for definitive diagnosis if displaced viscera or a hernial ring cannot be identified. Small amounts of omentum herniated through a small defect cause persistent wound swelling and is rarely diagnosed without wound exploration.

Treatment

Acute Incisional Hernias

Most incisional hernias should be repaired without delay unless they are chronic and freely reducible. Prognosis dramatically worsens if evisceration occurs. Immediate hospitalization and support of the hernia with bandages should be performed as the patient is prepared for surgery. Early surgical intervention is recommended for those patients with eviscerated hernias, or those with overlying skin incision breakdown or devitalization because exogenous contamination could result in fatal septic peritonitis.¹ 

The approach is made over the original incision unless organ damage is present; otherwise, a ventral midline approach may be used. When technical failure is suspected (knot, suture, or tissue failure) the entire wound is reopened and repaired. If one significant technical error is present in the hernial ring area, other adjacent areas are also at risk of impending breakdown. The surgeon should pay particular attention to identification of the strength-holding layer and include appropriately sized tissue bites (at least 5 mm) during suturing of this layer. Acute incisional hernias are repaired with primary musculofascial reconstruction if adequate tissue is present to close the hernia without undue tension. The surgeon should remove fat completely between edges to be approximated. Knots are carefully tied with the appropriate number of snug square throws and attention is paid to intrinsic suture tension to avoid crushing tissue. Debridement is contraindicated during repair of acute incisional hernias unless wound edges are nonviable or necrotizing fascial tissue is present. Removing healthy wound edges creates excessive and unnecessary tissue trauma and spreads contamination into sterile areas. Debridement of this actively healing tissue sets the wound back to the substrate phase and delays the onset of rapid wound strength gain.

Chronic Incisional Hernias

Chronic incisional hernias that are not incarcerated have enough strength in the overlying hernia sac and skin to prevent evisceration, so these hernias may be repaired on an elective basis or conservatively managed.¹ Palpable adhesions to protruding organs are, however, indications for early surgical intervention because adhesions may cause obstruction, torsion and vascular compromise of entrapped tissue.

Conservative management of asymptomatic patients with small hernias should be considered only if the patient’s owners can be trusted with wound monitoring. Affected patients require daily hernia palpation. Pain, discoloration, incarceration, and rapid increase in hernia size are indications for immediate examination of the animal by the veterinarian. Chronic hernias usually do not cause significant patient discomfort, however, they may be of concern when the animal is used for breeding.⁴ Large hernias may prevent delivery (causing dystocia) because of uterine incarceration or lack of adequate abdominal contraction during labor.

Chronic incisional hernias are usually approached surgically over the original incision area. Muscle edges may retract some distance away from the defect, producing a functional loss of abdominal wall. This results in excessive tension during primary hernia repair and thus increases recurrence risk.^7,18

A major technical difficulty in repair of chronic incisional hernias is accurate identification of normal tissue layers. Surgical dissection and accurate identification of primary strength-holding tissue at hernia margins are critical for lasting repair. Simple imbrication of the hernial sac without extensive scar excision from the hernial ring usually results in recurrence of the hernia because of attenuation of the relatively weak scar tissue. In chronic hernias, muscle and subcutaneous tissues are usually scarred together in one layer. Conservative excision of surrounding scar tissue is recommended until identification of the strength-holding layer is possible.

A condition termed “loss of domain” occurs when the abdominal cavity has become accustomed to a smaller intra-abdominal volume than normal. A functional loss of abdominal wall occurs in this instance. As a result, reduction of the hernial contents and primary closure of the (usually large) defect may be impossible. Closure of the abdominal wall by forcing herniated contents back into the abdomen results not only in excessive tension on the repair, but also in acute pulmonary compromise from restriction of diaphragm function.⁷ In most veterinary patients with large chronic defects or areas of abdominal tissue loss, surgical repair is performed with prosthetic materials such as polypropylene mesh.^7,19

Evisceration

Patients presenting with evisceration require early aggressive supportive therapy. Control hemorrhage and cover exposed organs with sterile bandages to reduce further contamination and tissue damage until vital diagnostic tests are performed and stabilization is attempted. In addition, an Elizabethan collar is placed on the patient if constant monitoring is not possible. Exposed organs are quickly mutilated by animals, and the result is shock from fluid and blood loss. Sepsis may occur from severe wound contamination, particularly when intestines have been violated. Therefore, appropriate crystalloid and colloidal fluid and antibiotic therapy are critical for patient stabilization.

Wound preparation is performed in a clean area after anesthetic induction. The surgeon should avoid contact between potentially irritating and toxic antiseptics and cleansing agents, and the patient’s exposed organs during skin preparation. Exposed tissue is covered with saline soaked laparotomy sponges and a larger area of the abdomen is clipped, if necessary. The skin surrounding the wound is prepared routinely. In an aseptic area, the original abdominal wound is extended, if necessary, to explore abdominal viscera completely. The surgeon copiously lavages exposed but viable organs outside the abdominal cavity before further exploration. After isolating damaged areas from the rest of the viscera with laparotomy sponges, the surgeon resects nonviable and irreversibly damaged areas, and repairs organs when necessary. Appropriate specimens are submitted for culture and susceptibility testing. The abdomen is copiously lavaged to help remove particulate foreign material and gross contamination. The decision whether to close the abdominal wall and superficial tissues depends on the amount and location of tissue damage and wound contamination observed at surgery. Primary repair is appropriate for acute herniation with little tissue damage or contamination. Patients with minimal intra-peritoneal but significant superficial tissue damage or contamination should have routine abdominal wall closure with closed suction drainage.²⁰ Superficial tissue layers are best left open for necessary drainage and tangential debridement. Deep, severely contaminated wounds may be managed by an open peritoneal drainage technique.²¹

Aftercare and Prognosis

Postoperative management of patients after repair of acute, closed, incisional hernias is similar to postoperative care of patients that have undergone elective abdominal surgery. Exercise is strictly limited for at least 2 weeks. Extended exercise restriction should be considered if the wound developed complications such as seroma or infection, or if synthetic mesh was used in the repair. Careful observation of the wound is critical for detection of early signs of infection. If infection occurs, the skin and subcutaneous tissue sutures are removed and the wound is left open for second intention healing. A superficial infection is not necessarily fatal to the success of the repair but the longer the infection is present before treatment the more likely the wound will disrupt.¹⁹

When evisceration has occurred, the nature of the organ damage and repair, and patient status dictate postoperative treatment and monitoring. Intense monitoring and treatment are needed if shock and septic peritonitis are present. Fluid deficits are replenished and infection is treated with antibiotics and appropriate wound drainage. Nutritional management in these critical patients often is the major factor influencing prognosis.

Most patients with incisional hernias have a good prognosis after repair provided initiating causal factors were eliminated and minimal damage occurred to deep structures. Consequently, since most incisional hernias are usually closed and a result of technical failure, most patients have an excellent prognosis as long as appropriate repair was performed. Septic patients with severe peritoneal contamination and organ damage warrant a poor prognosis.²¹

References

1. Smeak DD: Abdominal hernias. In Slatter DH, ed.: Textbook of Small Animal Surgery. Philadelphia: W B Saunders Co., 2003, p 449.
2. Akman PC: A study of five hundred incisional hernias. J Int Coll Surg 37:125, 1962.
3. George CD, Ellis H: The results of incisional hernia repair: A twelve year review. Ann R Coll Surg Engl 68:185, 1986.
4. Gibson KT, et al: Incisional hernias in the horse. Incidence and predisposing factors. Vet Surg 18:360, 1989.
5. Rosin E: Single layer, simple continuous suture pattern for closure of abdominal incisions. J Am Anim Hosp Assoc 21:751, 1985.
6. Crowe DT: Closure of abdominal incisions using a continuous polypropylene suture: Clinical experience in 550 dogs and cats. Vet Surg 7:74, 1978.
7. Larson GM, Vandertoll DJ: Approaches to repair of ventral hernia and full thickness losses of the abdominal wall. Symposium of hernias. Surg Clin North Am 64:335, 1984.
8. Alexander HC, Prudden JF: The causes of abdominal wound disruption. Surg Gynecol Obstet 122:1223, 1966.
9. Ponka JK: Herniation of the Abdominal Wall. W.B. Saunders, Philadelphia, 1980.
10. Fisher GD, Turner FW: Abdominal incisional hernias: A ten year review. Can J Surg 17:202, 1974.
11. George CD, Ellis H: The results of incisional hernia repair: A twelve year review. Ann R Coll Surg Engl 68:185, 1986.
12. Nilsson T: Abdominal wound repair: An experimental study of the wound healing mechanism in the rabbit. Dan Med Bull 30:394, 1983.
13. Rosin E, Robinson GM: Knot security of suture materials. Vet Surg 18:269, 1989.
14. Hoer J, Klinge U, Schachtrupp A, et al.: Influence of suture technique on laparotomy wound healing: an experimental study in the rat. Langenbecks Arch Surg 386:218, 2001.
15. Smedberg SG, Broome AE, Gullmo A: Ligation of the hernia sac? Surg Clin North Am 64:299, 1984.
16. Ellis H: The cause and prevention of postoperative intraperitoneal adhesions. Surg Gynecol Obstet 133:497, 1971.
17. Ingle-Fehr JE, Baxter GM, Howard RD, et al.: Bacterial culturing of ventral midline celiotomies for predication of postoperative incisional complications in horses. Vet Surg 26:7, 1997.
18. Boyd JB: Tissue expansion in reconstruction. South Med J 80:430, 1987.
19. Smeak DD: Management and prevention of surgical complications associated with small animal abdominal herniorrhaphy. Gastrointestinal surgical complications. Probl Vet Med 1:254, 1989.
20. Mueller MG, Ludwig LL, Barton LJ: Use of closed-suction drains to treat generalized peritonitis in dogs and cats: 40 Cases (1997-1999). J Am Vet Med Assoc 219:789, 2001.
21. Woolfson JM, Dulisch ML: Open abdominal drainage in the treatment of generalized peritonitis in 25 dogs and cats. Vet Surg 15:27, 1986.
     

A hernia is an abnormal protrusion of an organ or tissue through a normal body opening. True hernias have a hernial ring and a sac formed of peritoneum surrounding the hernia contents; false hernias lack the peritoneal sac. Hernias are either reducible or irreducible. Irreducible hernias can become strangulated if the circulation to the contents becomes interrupted.

Inguinal hernias are formed when an organ or tissue protrudes through the inguinal canal. Indirect inguinal hernias, the most common type, occur when tissue protrudes through the normal evagination of the vaginal process in females or the vaginal tunica in males. A direct inguinal hernia occurs when the peritoneal evagination occurs separate from, and lies alongside the vaginal process or vaginal tunica as a separate outpouching of tissue.

Surgical Anatomy

The inguinal canal is a passage through the abdominal wall. During development, it is occupied by the gubernaculum of the testis, the vaginal tunic that will ensheathe the descended testis, the descending testis, and the spermatic cord, which consists of the vessels, nerves, and ductus deferens. In the bitch, the gubernaculum persists within the broad ligament of the uterus as the round ligament that traverses the inguinal canal.¹ In the female cat the vaginal process is absent.² In veterinary anatomy, it is customary to consider the inguinal canal as the passage between the internal inguinal ring and the external inguinal ring.¹ The cranial boundary of the internal inguinal ring is formed by the caudal edge of the insertion of the internal abdominal oblique muscle. It is bordered ventromedially by the rectus abdominis muscle and the prepubic tendon and caudally and laterally by the edge of the pelvis and the arcus inguinalis.³ The external inguinal ring is formed as a slitlike orifice in the insertion of the external abdominal oblique muscle and overlies the internal inguinal ring. The anatomy of the inguinal canal varies among species, depending on the caudal extent of the internal abdominal oblique muscle.¹

Etiopathogenesis

The exact etiopathogenesis of inguinal hernias is unknown. Congenital inguinal hernias have been noted in certain breeds. Inguinal hernias have been shown to be hereditary in the basenji, regressing spontaneously by 12 weeks of age.² Other breeds exhibiting a greater risk of inguinal hernias include the basset hound, cairn terrier, Pekingese, and West Highland white terrier. The Pekingese also exhibits a greater incidence of concurrent umbilical hernia.³ The cause of congenital inguinal hernias is unknown, but the disorder has been attributed to normal anatomic variations, polygenic inheritance, and infectious diseases.³

Acquired inguinal hernias are noted most often in the middle-aged intact bitch.^4-6 Most cases of herniation occur in the estral or pregnant bitch, suggesting hormonal involvement. Inguinal hernia has not been reported in the neutered bitch.⁶ Other factors that may be involved include weakening of the abdominal wall, trauma, obesity, and the accumulation of fat in the vaginal process.^1,5

Clinical Signs and Diagnosis

Most dogs with inguinal hernias have a soft, doughy mass in the inguinal region that is usually not painful on palpation. The mass can have been present for up to a year and may or may not be reducible on palpation. Elevation of the patient’s hindquarters may aid the examiner in reducing the hernia and allows palpation of the defect in the abdominal wall. The hernia can contain a gravid or infected uterus that is unable to be reduced. Other tissues and organs that can be contained within the hernia include omentum, intestine, bladder, prostatic fat, and spleen. Diagnosis of inguinal herniation is aided by radiography demonstrating gas-filled loops of intestine or the appearance of the ossifying fetal skeleton after 43 to 45 days of gestation. The bladder can be identified by contrast radiography after catheterization and aspiration of bladder contents. Inguinal hernia must be differentiated from subcutaneous fatty tissue accumulation, abscess, hematoma formation, and mammary gland neoplasia. The hernia can appear as a swelling lateral to the vulva and must be differentiated from a perineal hernia.⁷

Surgical Techniques

A ventral midline incision can be used for all inguinal hernias. This approach allows visualization of both inguinal rings and repair of bilateral herniation through a single incision. It also permits extension of the incision cranially, when necessary, without invasion of mammary tissue or its blood supply.^5,8

The surgical incision extends from the cranial brim of the pelvis as far cranially as necessary to allow exposure of the hernial sac. This incision is continued through the subcutaneous tissue down to the ventral rectus sheath. Dissection proceeds bluntly under the mammary tissue, and the mammary tissue is undermined and retracted laterally to expose the superficial inguinal ring and hernial sac (Figure 38-1). After the hernial sac is dissected from the subcutaneous tissue, the hernial sac is opened, and the contents are inspected (Figure 38-2). Any adhesions between the sac and the viscera are broken down, and the contents are returned to the abdominal cavity.

In some cases, it may be necessary to enlarge the hernial ring cranially to facilitate reduction of the hernia. If the urinary bladder is included in the hernia, aspiration of urine facilitates reduction. When one or both horns of the uterus are included and ovariohysterectomy is performed, extending the incision in a cranial and medial direction may be necessary to complete the procedure.^4,5
 

Should the hernia contain a gravid uterus, up to the seventh week of pregnancy the hernia can be replaced into the abdomen and the pregnancy can be allowed to continue to completion. After the seventh week of pregnancy, ovariohysterectomy is recommended, depending on the age and value of the bitch as a breeding animal.⁵

After replacement of viscera into the abdomen, the redundant sac is trimmed at the margins of the superficial inguinal ring. Twisting the redundant sac may help to maintain reduction of the contents within the abdomen (Figure 38-3). The hernial ring is sutured with simple interrupted sutures of 2-0 nonabsorbable suture material (Figure 38-4).⁹ Care must be taken during closure to avoid the external pudendal vessels and genitofemoral nerve, which exit from the caudomedial aspect of the ring. In males, the inguinal ring must be closed without compromising the spermatic cord as it traverses the inguinal canal.

The inguinal ring on the other side is inspected, the vaginal process in female dogs or the vaginal tunic in males is removed, and the ring is sutured closed. The mammary tissue is then drawn back to the midline, and the subcutaneous tissues are closed using absorbable sutures, with care taken to eliminate potential dead space. If necessary, a Penrose drain can be placed before closure and made to exit from a separate stab incision ventrally if a large amount of dead space in which fluid could accumulate is present. The skin is closed routinely.
 

Postoperative Care

The caudal abdomen is bandaged immediately after the procedure. Bandaging helps to eliminate dead space and increases the comfort of the patient. If used, drains should be covered with an absorbent dressing and bandage and can be removed 3 to 5 days postsurgicaly, before the patient’s discharge from the hospital. Broad-spectrum antibiotic treatment is used if a drain is in place and for 3 days after drain removal.

References

1. Ashdown RR. The anatomy of the inguinal canal in the domesticated mammals. Vet Rec 1983;75:1345-1351.
2. Fox MW. Inherited inguinal hernia and midline defects in the dog. J Am Vet Med Assoc 1963,143:602-604.
3. Hayes HM Jr. Congenital umbilical and inguinal hernias in cattle, horses, swine, dogs, and cats: risk by breed and sex among hospital patients. Am J Vet Res 1974;35:839-842.
4. Archibald J, Sumner-Smith G. Hernia. In: Archibald J, ed. Canine surgery. 2nd ed. Santa Barbara, CA: American Veterinary Publications, 1974.
5. North AF Jr. A new surgical approach to inguinal hernias in the dog. Cornell Vet 1959;49:379-383.
6. Smeak DD. Caudal abdominal hernias. In: Slatter DH, ed. Textbook of small animal surgery. 2nd ed. Vol. 1. Philadelphia: WB Saunders, 1985.
7. Blakely CL. Perineal hernia. In: Mayer K, LaCroix JV, Hoskins HP, eds. Canine surgery. 4th ed. Evanston, IL: American Veterinary Publishers, 1957.
8. Peddie JF. Inguinal hernia repair in the dog. Mod Vet Pract 1980;61:859-861.
9. Bojrab MJ. Inguinal hernias. In: Bojrab MJ, ed. Current techniques in small animal surgery. 2nd ed. Philadelphia: Lea & Feb-iger, 1983.
    

Introduction

The perineum is the region that closes the pelvic outlet, surrounding the anal and urogenital canals.¹ On the surface of the dog, the perineum is limited by the tail dorsally, the scrotum or beginning of the vulva ventrally, and the ischiatic tuberosity on both sides. Deeply, the perineum is bounded by the third caudal vertebra dorsally, the sacrotuberous ligaments on both sides (absent in cats), and the arch of the ischium ventrally. The pelvic diaphragm is the vertical closure of the pelvic canal through which the last segments of the digestive and urogenital viscera pass.²

Perineal hernia is the result of weakness and separation of the muscles and fascia that make up the pelvic diaphragm. The pelvic diaphragm is composed of levator ani and coccygeus muscles, and the internal and external perineal fascia.¹ The exact cause of the muscular weakness is unknown but several factors have been proposed.^3-14 As a result of the muscular weakness, caudal displacement of intra-abdominal organs or deviation or dilation of the rectum into the perineum can occur.^3,4 Retroflexion of the urinary bladder occurs in approximately 20% of the cases.^15,16 Other intra-abdominal contents found within the hernial sac include jejunum, colon, and prostate.¹⁶ The hernial space often contains retroperitoneal fat and fluid with or without abdominal and/or pelvic organs.¹⁷ 

Perineal hernia has been reported in multiple species, but is most problematic in dogs. Some breeds of dogs are over-represented in the occurrence of perineal herniation. Boston terriers, Pekingese, collies, boxers, Welsh corgis, kelpies, miniature poodles, German shepherd dogs, Bouviers de Flandres, old English sheepdogs, dachshunds, and mongrels have all been shown to have an increased incidence.^9,15,17 Perineal hernia occurs commonly in the male dog, particularly in sexually intact males, and rarely in females. Most dogs with perineal hernia are between 7 and 9 years of age.^9,18 

Perineal herniation may be unilateral or bilateral. Some investigators have reported an increased incidence of perineal herniation on the right side, but the criteria used to determine unilateral versus bilateral and left versus right are subjective. In fact, the occurrence of the hernia on one side versus the other may be related to the rate and extent of tissue deterioration rather than one side being affected preferentially.¹⁷

Clinical Signs

Tenesmus, constipation and perineal swelling are the three most consistent clinical features of dogs presented with perineal hernia.^3,17 In as high as 80% of dogs presented for perineal hernia, straining to defecate was the primary complaint. Tenesmus is the result of excessive feces that collect in a rectal dilatation or sacculation in the perineal hernia.⁴ Furthermore, the perineal swelling may be the combination of abdominal contents and/or a feces-filled rectum.

Retroflexion of the urinary bladder into the perineal hernia may result in urinary obstruction. The obstruction results from an abrupt change in direction of the urethra.¹⁶ Clinical signs associated with bladder retroflexion include stranguria, dysuria, and anuria.¹⁶ Although perineal hernia is not considered a surgical emergency, immediate repositioning of the bladder or urine evacuation is required. If the bladder cannot be reduced and urine evacuation cannot be achieved, surgical intervention on an emergency basis may be required.

Other less commonly reported clinical signs have been depression/lethargy, vomiting, anorexia, perineal pain, stringy stool, weight loss, and fecal incontinence.¹⁵

Diagnosis

The diagnosis of a perineal hernia is based on the history, clinical signs, physical examination, and radiography. The diagnosis may be difficult during the early stages when the hernia is forming.³ However, with progression of the clinical signs, the diagnosis usually becomes more obvious. Rectal palpation is the most important part of the physical examination when diagnosing perineal hernia. When performing a rectal examination, the index finger is directed cranially into the middle of the herniated rectum which lies lateral to the anus and medial to the wall of the pelvic canal.¹⁹ Generally, the rectum is filled with feces making identification of the extent (unilateral versus bilateral) of the hernia difficult. Manual removal of the fecoliths from the rectum allows better assessment of the pelvic diaphragm muscles. When evaluating the rectum for abnormalities such as a deviation, sacculation, or diverticulum, a rectal barium enema⁴ may be helpful, but is usually not necessary. Differentiation between rectal sacculation (full-thickness outpouching of the rectal wall) and diverticulum (protrusion of mucosa/submucosa through a muscular defect) requires inspection of the muscular coat of the rectum at surgery.

When there are clinical signs of urinary tract involvement with a perineal hernia, caudal abdominal radiography including the perineum are performed. The contents of the perineal hernia and the location of the urinary bladder is identified. If the urinary bladder cannot be visualized on routine radiography, retrograde urethrography and/or cystography can be done.^3,16 Alternately, ultrasonography can be used to identify the location of the urinary bladder (either within the hernia or abdomen) and can be used to assist decompression via syringe and needle.

Conservative Therapy

Conservative management of perineal hernia includes the use of stool softeners, periodic enemas, and digital evacuation of the feces from the rectum as needed.^3,17 Dogs considered for conservative medical and dietary management include dogs that are poor anesthetic/surgical candidates because of known organ disease and dogs with owners who refuse to have surgery performed.^3,20 Dogs with straining as the primary clinical complaint during the initial presentation are reported to have a poor response to medical management over an extended period of time.²⁰

Hormonal therapy either by castration, low-dose estrogen therapy, or progestins can decrease the size of the prostate and alleviate clinical signs associated with prostatic hyperplasia. However, there are no reported studies that have evaluated the efficacy of hormonal therapy on controlling the long-term clinical signs associated with prostatomegaly and a concomitant perineal hernia.¹⁷ Castration is recommended by the authors because of its beneficial effects regarding prostatic disease prophylaxis despite its questionable role in perineal hernia recurrence prevention. The authors caution against other forms of hormonal therapy for prostatic disease since severe and fatal complications such as bone marrow aplasia may result.

Surgical Anatomy

The structures involved in surgical repair of perineal hernia include the pelvic diaphragm, the perineal fasciae, and the nerves and vessels in the proximity of these structures (Figures 38-5 and 38-6). Additionally, extraperineal muscle flaps can be transposed for perineal herniorrhaphy (i.e., the semitendinosus muscle flap).²¹
 

The levator ani and coccygeus muscles originate from the medial side of the ischial spine and medial side of the body of the ilium/ dorsal surface of the pubis cranial to the obturator foramen, respectively. The levator ani and coccygeus muscles insert on the third through seventh caudal vertebrae, and the first through the fourth caudal vertebrae, respectively. These two muscles form the lateral boundary for the rectum or the medial boundary of the pelvic diaphragm.^2,20

The sacrotuberous ligament and the superficial gluteal muscle form the lateral aspect of the pelvic diaphragm. The sacrotuberous ligament originates from the ischiatic tuberosity and inserts on the sacrum and first caudal vertebra. The superficial gluteal muscle originates on the lateral aspect of the sacrum, first caudal vertebra, and the cranial half of the sacrotuberous ligament. The superficial gluteal muscle forms a tendon lateral to the perineal region and runs over the dorsal aspect of the greater trochanter to insert on the third trochanter.^2,20

The ventral aspect of the perineal region is bounded by the internal obturator muscle, which can be transposed for perineal herniorrhaphy. The internal obturator muscle originates on the cranial and medial border of the obturator foramen and the internal surface of the ischium (ischiatic table), and inserts as a flat tendon embedded in the bellies of the gemelli muscles in the trochanteric fossa of the femur.^2,20

The external anal sphincter muscle is a striated muscle that surrounds the anal canal. This muscle is divided into three parts: the cutaneous part, the superficial part, and the deep part. The cutaneous part lies directly under the skin in the subcutaneous fascia. The superficial part attaches to the third and fourth caudal vertebrae and passes around the lateral aspect of the anus and anal sacs to insert on the bulbocavernosus muscle (male) or the constrictor muscle of the vulva (female). The deep part surrounds the anal canal, passing medial to the anal sacs. The superficial and deep parts can interchange with each other.^2,17

The semitendinosus muscle is a striated muscle that originates from the ischiatic tuberosity and inserts on the tibia and on the tuber calcanei.¹ Although it does not directly bound the perineal region, the semitendinosus muscle has been used to reconstruct perineal hernia defects.²¹

The internal pudendal artery and vein, and the pudendal nerve are bound together by loose connective tissue, and this neurovascular bundle passes ventrolaterally to the coccygeus muscle and continues caudomedially across the dorsal surface of the internal obturator muscle. At the caudal border of the ventral aspect of the external anal sphincter muscle, the pudendal nerve gives off the caudal rectal nerve. This branch of the pudendal nerve provides motor innervation to the external anal sphincter muscle.²

The perineal fascia is the connective tissue covering of the perineal musculature and is divided into deep and superficial layers. The deep perineal fascia is the fascia that tightly covers the musculature. The superficial perineal fascia is the loose connective tissue that makes a thin hernial sac. The superficial perineal fascia is not considered to be of adequate strength to suture as the primary layer for hernia repair.

Patient Preparation

A perineal hernia is not usually considered a surgical emergency unless the urinary bladder is retroflexed.¹⁶ If the urinary bladder is retroflexed into the perineal hernia, the urinary bladder should be manually reduced. If the urinary bladder cannot be reduced, a urinary catheter should be placed or paracentesis must be performed. Removal of urine from the urinary bladder should assist in reduction. Serum biochemistries (serum urea nitrogen and creatinine) should be evaluated. Dogs with azotemia should be treated appropriately and surgery postponed until the patient is stable.¹⁶

If the perineal hernia does not contain the urinary bladder, the surgical repair is a nonmergent procedure. Since the majority of dogs with perineal hernias are geriatric, a minimum data base including a complete blood count, serum biochemistries, thoracic radiographs and a complete urinalysis should be performed.³

Some surgeons prepare the dog for surgery by having the rectum cleaned of all feces with several enemas the day before surgery, and by fasting the dog for 24 hours prior to surgery. Enemas run the risk of rectal trauma and make for fluid fecal material which is difficult to contain during surgery; therefore, the authors prefer to avoid enemas. Instead, gentle digital extraction of feces is performed after the dog is anesthetized immediately prior to surgery.

After the dog is anesthetized, the perineal region is liberally clipped. The anal sacs are evacuated, a lubricated gauze tampon is inserted into the rectum, and a purse-string suture is placed in the anus. A preliminary scrub is performed to remove gross contamination from the perineum. The dog is positioned in sternal recumbence at the end of the surgical table (Figure 38-7A and B). The pelvic limbs are placed off the end of the table and are gently pulled forward. The table can either be tilted forward, or the dog can be placed in a perineal stand. If a perineal stand or tilt table are not available, sand bags or other padding can be used to elevate the dog’s perineum. When pulling the pelvic limbs over the end of the table, the front of the limb should be protected by padding to prevent femoral and fibular (peroneal) nerve injury. If a tilt table is used to help position the dog, excessive tilting of the table should be prevented because of the concern for respiratory compromise. Since the perineal position causes the dog’s head to be placed downward, the abdominal contents encroach on the diaphragm and intermittent positive pressure ventilation is required.

After the patient is positioned, the tail can be wrapped and adhesive tape placed above the base of the tail and then directed towards the dog’s head. This pulls the tail over the dog’s back. After the tail has been positioned, a final scrub can be performed.

Perioperative antibiotics are used by some surgeons; however, the use of antibiotics should not preclude good aseptic surgical technique. If antibiotics are chosen, a broad spectrum antibiotic with activity against gram-negative enteric organisms should be used.
 

Surgical Technique

Draping of the perineal region should be performed so that none of the anus is exposed after the skin incision is made, but accessible to visualization if necessary. Castration is performed on sexually intact male dogs prior to herniorrhaphy. Caudal castration²² may be performed with the dog in the perineal position to decrease the overall length of the surgical procedure by avoiding the repositioning associated with standard prescrotal castration.

We prefer the internal obturator muscle transposition technique for perineal herniorrhapy. If there is questionable integrity of the internal obturator muscle, porcine small intestinal submuscosa (SIS) may be used in place of the obturator muscle.^23,24 Understanding the surgical anatomy and manipulations for the internal obturator and SIS techniques is facilitated by an understanding of the traditional perineal herniorrhaphy procedure. Therefore, the traditional technique is discussed first below.

Traditional Perineal Herniorrhaphy

The incision is made over the hernia from just lateral of the tail base to just below the hernial mass (See Figure 38-7A and B). The incision is curved slightly laterally in a dorsoventral direction. Care must be taken to not incise too deeply and injure the hernial contents.

Blunt dissection is used to enter the hernial sac (superficial perineal fascia) and expose the hernial contents. Once the contents of the hernia are exposed, redundant fat can be excised and hernial fluid removed. If jejunum, prostate, colon, or urinary bladder are encountered, these structures can be reduced by digital manipulation in a cranial direction back to their pelvic or abdominal location and maintained with a gauze sponge. A suture can be tied to the gauze sponge to facilitate its removal prior to tying the herniorrhaphy sutures.

Following reduction of the hernia, the muscular defect and landmarks for surgical closure are identified (Figure 38-8). The medial side of the defect is bounded by the rectum, ending with the anal sphincter muscle caudally. The coccygeus muscle and, if present, the levator ani muscle are dorsolateral to the defect. The sacrotuberous ligament can be palpated as the lateral landmark of the repair. This ligament is a broad fibrous cord that extends from the sacrum and first caudal vertebra to the ischiatic tuberosity. The ventral boundary of the hernia is formed by the internal obturator muscle on the floor of the pelvis. Ventrolateral to the coccygeus and levator ani muscles and dorsal to the internal obturator muscle is the neurovascular bundle (internal pudendal artery and vein, and pudendal nerve) of this region. Identification of the neurovascular bundle is important because the pudendal nerve supplies motor function to the external anal sphincter muscle. Bilateral pudendal nerve injury may result in permanent fecal incontinence.³ Unilateral pudendal nerve injury may lead to temporary incontinence until reinnervation or compensation from the opposite side occurs.

Before pelvic diaphragm repair the presence or absence of rectal disease must be ascertained.^4,8 Rectal deviation occurs as a result of a potential space created by the hernia. Perineal herniorrhaphy should alleviate rectal deviation and small sacculation. Large rectal sacculation and rectal diverticulum may cause straining to expel feces. Therefore, surgical excision of rectal diverticulum or large sacculation, followed by an inverting suture pattern, should be performed to prevent perineal hernia recurrence due to straining caused by impacted feces.⁴
 

All herniorrhaphy sutures should be preplaced before they are tied (Figure 38-9). The authors recommend synthetic nonabsorbable monofilament suture such as polypropylene for the primary closure of the hernial defect. Suture placement is begun from the most ventral aspect of the defect. The first suture is placed from the internal obturator muscle laterally to the external anal sphincter muscle medially, or vice versa, depending on the side of the hernia and the surgeon (right- versus left-handed). Care should be taken when passing sutures through the internal obturator muscle to not incorporate sutures into the neurovascular bundle in this region. Since the recurrence rate is high with the traditional suture technique, placement of an adequate number of sutures ventrally is important to success.³ Additional sutures are placed dorsally to the internal obturator suture(s) incorporating bites from the external anal sphincter into the sacrotuberous ligament, the coccygeus muscle, and, when present, the levator ani muscle.³ When placing sutures through the sacrotuberous ligament, care must be taken to not include the caudal gluteal artery/vein or the sciatic nerve which lie cranial to the ligament. Placing a finger medial and cranial to the sacrotuberous ligament may assist in determining the depth of suture placement by palpation of the caudal gluteal artery’s pulse.³ Furthermore, the suture should be placed through the fibers of the sacrotuberous ligament instead of encircling the entire structure. When placing sutures through the external anal sphincter muscle multiple fibers are gathered onto the needle. Care should be taken to avoid penetration of the rectum or anal sac(s). Once all sutures are preplaced they are tied from dorsal to ventral. As sutures are tied the anus may be visualized to ensure that it has not been grossly distorted.

Following closure of the hernial defect, the superficial perineal fascia is mobilized laterally from the skin. After mobilization, the perineal fascia can be used to reinforce the closure by suturing the fascia caudally to the external anal sphincter muscle using synthetic absorbable suture material. The subcutaneous tissue and skin are closed routinely. Strategic subcutaneous suture placement to minimize dead space eliminates the need for placement of drains. Drains are to be avoided in the perineal region because of postoperative contamination risks.

If bilateral hernia repair is considered, the hernias can be repaired at the same surgery; however, some surgeons will wait 4 to 6 weeks between repairs to decrease the stress and distortion of the external anal sphincter muscle associated with the traditional herniorrhaphy technique.³

We believe that castration should be performed for its benefits relative to treating prostatic disease. It is unlikely that castration prevents pelvic diaphragm muscle weakness.^12,13,25
 

After all procedures have been completed, the anal purse-string suture and rectal gauze tampon are removed. A thorough rectal examination should be performed to evaluate the integrity of the repair.

Internal Obturator Muscle Transposition

With the dog ventrally recumbent in the perineal position a semicircular skin incision similar to the one used for the traditional herniorrhaphy technique is made in the perineal skin from the tail base to the median raphe ventrally. The subcutaneous tissue is carefully incised and the skin edges are retracted to expose the perineal structures (Figure 38-10). After the hernial contents are isolated and reduced, the internal obturator muscle is subperiosteally elevated from the ischiatic table starting caudomedially and proceeding laterally and cranially. The internal obturator tendon is cut just before it disappears beneath the sacrotuberous ligament, and the muscle is lifted dorsally (Figure 38-11). Failure to completely incise the internal obturator tendon may result in inadequate coverage of the hernia by the muscle. The transposed internal obturator muscle is sutured medially to the external anal sphincter and laterally to the sacrotuberous ligament, the coccygeus muscle, and, if present, the levator ani muscle using polypropylene sutures (Figure 38-12). Any residual defect in the dorsal aspect of the repair is closed with additional interrupted sutures from the coccygeus muscle to the external anal sphincter. The perineal fascia, subcutaneous tissue, and skin are closed in similar fashion to the traditional perineal herniorrhaphy technique.

Failure of internal obturator muscle transposition most commonly occurs in the ventromedial aspect of the transposed muscle. To prevent failure care should be exercised during subperiosteal elevation to prevent excessive trauma to the muscle, and the ventromedial sutures from the internal obturator muscle to the external anal sphincter should be secure.
 

Perineal Herniorrhaphy using Porcine Small Intestinal Submucosa (SIS)

The skin incision and surgical approach are similar to the traditional and obturator muscle transposition techniques. Once the hernia is reduced, a 4-ply sheet of SIS is trimmed to dimensions slightly larger than the defect in the pelvic diaphragm. Horizontal mattress sutures (synthetic, absorbable or nonabsorbable, monofilament) are pre-placed from the external anal sphincter, coccygeus muscle, sacrotuberous ligament, and internal obturator muscle to the SIS, leaving a 5 to 10-mm edge on the SIS. After all mattress sutures are placed, they are tied, resulting in closure of the pelvic diaphragm defect (Figure 38-13). Any residual defect in the dorsal aspect of the repair is closed with additional interrupted sutures from the coccygeus muscle to the external anal sphincter. The perineal fascia, subcutaneous tissue, and skin are closed in similar fashion to the traditional perineal herniorrhaphy technique.
 

Postoperative Management

Efforts should be made to ensure a smooth recovery from anesthesia to prevent undo stress on the repaired perineum. To this end, light sedation is occasionally necessary in conjunction with routine analgesics in the early postoperative period.

Prophylactic use of antibiotics to lower the incidence of infection with perineal hernia repair is not straightforward. In a retrospective evaluation of 100 dogs, the authors recommended the use of perioperative antibiotics rather than administering antibiotics after surgery unless an infection has been documented.¹⁵ Good aseptic surgical technique is more important than antibiotics to prevent infection. We select prophylactic antibiotics on an individual case basis.

A low-residue diet can be fed the first few days to help prevent straining during defecation which may lead to disruption of the perineal hernia repair. If straining to defecate does not resolve, digital palpation should be performed to rule out a suture placed in the rectal mucosa. If a suture is not the cause for straining, the pain usually resolves, but analgesics may be necessary in the interim.

If the dog chews or licks excessively at the incision, an Elizabethan collar or similar restraint device should be used to prevent the dog from chewing or licking the incision. Dogs should be returned in 10 to 14 days for skin suture removal.

Complications

Several potential postoperative complications can be associated with repair of perineal hernia. These complications include sciatic nerve injury; fecal incontinence; infection around the incision site; rectal prolapse associated with excessive straining; misplacement of sutures into the anal sac(s) or rectal lumen; urinary bladder necrosis; urinary incontinence; and recurrence of the perineal hernia.²⁵ Recognition, prevention and appropriate management of these postoperative complications are essential to a successful surgical outcome.

Sciatic nerve injury or entrapment can occur if the nerve becomes encircled or is penetrated by a suture passed around the sacrotuberous ligament. Entrapment of the sciatic nerve is identified immediately after recovering from surgery. The dog will show signs of extreme pain over the hip and perineal region. Furthermore, a sciatic nerve palsy may be detected on a neurologic examination. The treatment of sciatic nerve entrapment is removal of the suture through a caudolateral approach to the hip.²⁶ This surgical approach allows good visualization of the sciatic nerve and does not require disruption of the perineal hernia repair. Occasionally, epidural medicant administration is used for postoperative analgesia in patients having pelvic or perianal surgery. Because this analgesic technique can cause transient sciatic palsy, the authors recommend alternate means of controlling postoperative pain after perineal herniorrhaphy to avoid confusion with iatrogenic surgical injury to the sciatic nerve. Potentially, observation of sciatic palsy would subject the dog to unnecessary sciatic nerve exploration if the neurologic deficit was due to the epidural analgesic technique.

Fecal incontinence may be only temporary due to postoperative pain and inflammation associated with the surgery. Unilateral damage to either the pudendal nerve or the caudal rectal nerve may be associated with temporary incontinence that resolves after the contralateral caudal rectal nerve reinnervates the damaged nerve’s side.^17,25 Return of full fecal continence may take several weeks after unilateral caudal rectal nerve damage. Permanent fecal incontinence is likely if bilateral caudal rectal or pudendal nerve damage occurs, or if damage to the external anal sphincter muscle or other pararectal tissue is excessive.²⁵ Permanent fecal incontinence is best avoided because the reported prosthetic implants and muscle transpositions used for treatment have demonstrated inconsistent success in reestablishing fecal continence.^21,27

Incisional complications have been reported as a function of the surgical location.¹⁵ Exposure of the incision to feces either during surgery or before a good fibrin seal has occurred can cause a wound infection. If an infection occurs surgical drainage of the site and administration of antibiotics based on culture and susceptibility is ideal. If antibiotics need to be instituted without knowledge of culture and susceptibility, a broad spectrum antibiotic with activity against Escherichia coli should be used.²⁵

Rectal prolapse can sometimes occur immediately after surgery. Rectal prolapse can occur as a result of excessive straining postoperatively due to placement of suture(s) in the rectal lumen, or because of pain associated with bilateral hernia repair. Rectal disease and external anal sphincter nerve injury have been two other predisposing factors to rectal prolapse. The rectal prolapse should be reduced and a purse-string suture placed in the anus. If straining is excessive and unresponsive to narcotics, an epidural can be administered. The anal purse-string suture should be maintained until the straining has resolved. Generally, this may take several days. If the rectal prolapse recurs after multiple attempts at reduction, a colopexy should be performed.²⁵

Misplaced suture(s) into the rectal mucosa can occur because of difficulty in identifying perineal structures due to excessive tissue inflammation and swelling. Misplaced sutures can lead to excessive straining, or, uncommonly, development of a rectocutaneous fistula. Misplacement of suture(s) into the anal sac can also lead to draining tracts. The treatment of chronic fistulas associated with misplaced sutures is by fistulectomy and anal sacculectomy, depending on the anatomic structure involved.²⁵

Complications relative to retroflexion of the urinary bladder into the perineal hernia are seen infrequently. Retroflexion of the urinary bladder can stretch the nerves that supply the urinary bladder and urethral sphincter, stretch the detrusor muscle resulting in bladder atony, or interfere with the blood supply to the urinary bladder. Usually, clinical signs seen with this complication are temporary. Manual decompression of the urinary bladder or catheterization may be necessary to keep the urinary bladder empty until its muscle tone returns. Urinary bladder necrosis has been associated with long-standing cases secondary to urinary bladder obstruction and distention. The clinical signs secondary to urinary bladder necrosis are rupture and uroperitoneum. Exploratory celiotomy and resection of the necrotic portion of the urinary bladder may be required; however, in some cases, excessive urinary bladder necrosis may prohibit a successful resection.²⁵

Recurrence of a perineal hernia after repair has ranged from 5 to 46%.^8-11,28 Although some surgical procedures offer better results and less chance of recurrence, the accurate identification of all anatomic structures is paramount to the success of any procedure. Furthermore, understanding the limitations of each particular technique is important in the surgical decision-making process and may help in reducing the failure of any technique.

The association between castration and the recurrence of a perineal hernia after surgical repair has been reported to be 2.7 times greater in dogs that were not castrated versus those dogs that were castrated.⁹ However, in a later study, no correlation was found between castration and perineal hernia recurrence. Failure of perineal hernia repair was thought to be more related to lack of experience with the surgical technique than any effect from castration.¹⁵

Salvage Techniques for Failed Perineal Herniorrhaphy

Recurrence of canine perineal herniation following traditional herniorrhaphy has been reported to be as high as 46%.¹⁰ Recurrence rates as low as 5% have been reported for the internal obturator muscle transposition herniorrhaphy technique.¹¹ Nonetheless, until the ultimate cause of canine perineal hernia can be identified and controlled, a certain degree of recurrence can be expected regardless of refinements in surgical technique. When the traditional herniorrhaphy technique fails, the simplest and usually most effective means of salvage is to perform an internal obturator muscle transposition to reconstruct the pelvic diaphragm. Alternately, the SIS technique could be employed. When the internal obturator muscle transposition fails, SIS might be used to close the defect; however, absence of the internal obturator from its normal ischial location may make it difficult or impossible to anchor the SIS ventrally. When the internal obturator muscle transposition and SIS techniques are not options, the authors recommend choosing from one of the following two options: (1) semitendinosus muscle transposition^21,29 for perineal reconstruction or (2) colopexy/cystopexy^30-32 for preventing herniation of important structures. 

Semitendinosus Muscle Transposition

The semitendinosus muscle transposition is particularly useful for reconstructions in which the ventral aspect of the perineum is severely affected as is the case with some bilateral perineal hernias. For unilateral perineal herniation the contralateral semitendinosus muscle is recommended for pelvic diaphragm reconstruction.

With the dog in the perineal position a skin incision is made in the perineal skin from the tail base to the median raphe ventrally just as is done for traditional, internal obturator muscle transposition, and SIS repairs, and the incision is continued across midline toward the ischiatic tuberosity where it curves and progresses distally on the caudal aspect of the pelvic limb to end at the caudomedial aspect of the transition between the stifle and the crus (Figure 38-14). The hernial contents are exposed and reduced in similar fashion to other herniorrhaphy techniques prior to isolation of the semitendinosus muscle. The subcutaneous tissues over the semitendinosus muscle are incised to expose the muscle (Figure 38-15). The semitendinosus muscle is bluntly isolated from surrounding structures taking care not to injure the proximal vascular pedicle (the caudal gluteal artery and vein). The semitendinosus muscle is transected as distally as possible near the stifle and is further isolated for mobilization to the perineal region. Incision of the lateral portion of the semitendinosus tendinous attachment to the ischium may be necessary for maximal mobilization, but care must be taken to avoid proximal vascular pedicle trauma or kinking that may occur with excessive mobilization. Using polypropylene or nylon suture, the transected portion of the semitendinosus muscle is sutured to the sacrotuberous ligament and the coccygeus muscle. The medial aspect of the semitendinosus muscle (now adjacent to the external anal sphincter muscle dorsally) is sutured to the external anal sphincter, and the lateral aspect of the semiten- dinosus muscle (now adjacent to the ventral aspect of the perineum) is sutured to the remnant of the internal obturator muscle, the ischiourethralis muscle, perineal fasciae, and/or the periosteum of the dorsal surface of the ischium (Figure 38-16). Synthetic absorbable sutures are used to obliterate dead space and close the subcutaneous tissues. The skin is closed with the routine closure of the surgeon’s choice.
 

Colopexy/Cystopexy for Failed Perineal Herniorrhaphy Salvage

Colopexy with cystopexy via deferent duct fixation is designed to prevent herniation of the most problematic organs (colon, prostate, urinary bladder) that may become entrapped in the perineal hernia space. This technique is typically reserved for cases where perineal reconstruction using muscle transpositions have failed or when the surgeon anticipates failure of muscle transposition.

The dog is positioned in dorsal recumbence for ventral midline celiotomy (Figure 38-17). If the dog is not castrated, standard prescrotal castration is performed prior to celiotomy. Once the abdomen is open, the colon and urinary bladder are exposed by packing the other abdominal organs cranially with moist laparotomy sponges (Figure 38-18). Cranial traction is applied to the colon to reduce herniated rectum and prevent the rectum from migrating into the perineal space. The colon is secured in this position to the dorsolateral body wall with two staggered rows of mattress sutures (three to four mattress sutures per row) of polypropylene placed in full-thickness fashion through the colon (Figure 38-19).
 

A stay suture is placed in the apex of the urinary bladder to aid in exteriorization and exposure of the deferent ducts. Both deferent ducts are gently pulled into the abdomen from the vaginal canals. A stay suture is placed at the severed end of the left deferent duct to assist manipulation. A 1 to 2 cm belt loop is created dorsolaterally in the left transversus abdominis muscle midway between the left kidney and urinary bladder. The belt loop is created by making two stab incisions parallel to the transversus abdominis muscle fibers and bluntly dissecting beneath the muscle between the stab incisions with hemostatic forceps. The stay suture in the deferent duct is grasped with hemostatic forceps and pulled from caudal to cranial through the belt loop to pull the deferent duct through the loop until it is taught. The deferent duct is then folded back (caudally) over the belt loop and is sutured to itself and to the belt loop with simple interrupted polypropylene sutures (Figure 38-20). The manipulated end of the deferent duct with the stay suture is excised. The right deferent duct is secured to the right body wall in the same fashion. After removal of the laparotomy sponges and urinary bladder stay suture, the celiotomy is closed routinely.
 

Caudal Castration in the Dog

An alternative to standard prescrotal castration is desirable in dogs when castration is indicated in conjunction with perianal or perineal surgery. Although the role of castration in canine perineal hernia is debatable,¹³ many surgeons continue to perform castration in conjunction with perineal herniorrhaphy. Whenever a dog is undergoing castration at the same time as a procedure that requires perineal positioning, caudal castration can decrease operative time by eliminating the need for intraoperative repositioning.²²

Patient preparation: For caudal castration, the dog must be surgically prepared such that the scrotum is in the aseptic surgical field once the surgical drapes are in place. Therefore, gentle clipping of scrotal hair with a cool clipper blade is performed before clipping of the remainder of the surgical field. After clipping and hair removal are complete, the dog is placed in the perineal position (See Figure 38-7) for aseptic surgical preparation. We prefer to use chlorhexidine instead povidone iodine for scrotal disinfection, to minimize the chance of scrotal dermatitis. On completion of skin disinfection, surgical drapes are placed such that the scrotum is within the surgical field (Figure 38-21), and caudal castration is performed before the other scheduled surgical procedure (perineal herniorrhaphy, perianal adenoma excision). The anus and perianal region may be temporarily covered with drapes to minimize contamination of the castration procedure.

Surgical technique: The skin incision begins on the median raphe and extends ventrally onto the scrotum over the left testicle (Figure 38-22). Open castration is then performed. The left testicle is pushed toward the skin incision to allow incision of the internal spermatic fascia and parietal lamina of the vaginal tunic exposing the testicle. The excess internal spermatic fascia and parietal lamina of the vaginal tunic is excised, and the testicle is removed using a three clamp technique (Figure 38-23). The right testicle is approached through the same skin incision through the interdartoic septum and is removed in a fashion similar to that of the left testicle. A few subcutaneous subcuticular sutures of synthetic absorbable suture are used for closure. The perineal position is maintained for the subsequent surgical procedure, and the scrotum may be draped out of the surgical field to minimize contamination of the castration incision.
 

Perineal Herniorrhaphy in the Cat

The etiopathogenesis of perineal hernia in cats differs from that of dogs. In cats, perineal hernia may occur as a long-term complication of perineal urethrostomy or may be associated with megacolon. Feline perineal hernias that are not associated with either of these two situations are considered idiopathic; a hormonal influence has not been seriously considered because both genders are typically represented, most affected cats being spayed or castrated.^33-36 A left-sided perineal hernia in an 8-week-old cougar was thought to be congenital.³⁷ Most perineal hernias in cats are bilateral.³³

The perineal herniorrhapy techniques used in dogs may be applied to cats, but attention should be paid to anatomical differences. Feline perineal muscles are smaller than like muscles in the dog, and the cat does not possess a sacrotuberous ligament (Figure 38-24).^38,39 Because feline perineal hernia is often bilateral, the internal obturator muscle transposition is preferred to the traditional technique to avoid excessive tension on the external anal sphincter. Although not yet reported in cats at the time of this writing, SIS repair could also be performed. The semintendiosus muscle transposition repair has been reported in a cat.⁴⁰

Complications after perineal herniorrhaphy in cats seem to be less common than in dogs, but one should be vigilant for the same possible complications as described for dogs. Additionally, concurrent disease that might contribute to straining, such as megacolon, must be addressed for optimal success.
 

References

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22. Knecht CD. An alternate approach for castration of the dog. Vet Med/Small Anim Clin 1976;71:469-473.
23. Stoll MR, Cook JL, Pope ER, et al. The use of porcine small intestinal submucosa as a biomaterial for perineal herniorrhaphy in the dog. Vet Surg 2002;31:379-390.
24. Desai R. An anatomical study of the canine male and female pelvic diaphragm and effect of testosterone on the status of the levator ani of male dogs. J Am Anim Hosp Assoc 1982;18:195-202.
25. Matthiesen DT. Diagnosis and management of complications occurring after perineal herniorrhaphy in dogs. Comp Cont Ed Vet Pract 1989;11:797-823.
26. Piermattei DL, Johnson KA. Approach to the caudal aspect of the hip joint and body of ischium. In: Piermattei DL, Johnson KA, eds. An Atlas of Surgical Approaches to the Bones and Joints of the Dog and Cat. 4th ed. Philadelphia: Saunders, 2004, pp. 310-314.
27. Dean PW, O’Brien DP, Turk MA, et al. Silicone elastomer sling for fecal incontinence in dogs. Vet Surg 1988;17:304-310.
28. Orsher RJ. Clinical and surgical parameters in dogs with perineal hernia- analysis of results of internal obturator transposition. Vet Surg 1986;15:253-258.
29. Philibert D, Fowler JD. Use of muscle flaps in reconstructive surgery. Compend Cont Ed Pract Vet 1996;18:395-405.
30. Bilbrey SA, Smeak DD, DeHoff W. Fixation of the deferent ducts for retrodisplacement of the urinary bladder and prostate in canine perineal hernia.Vet Surg 1990;19:24-27.
31. Brissot HN, Dupré GP, Bouvy BM. Use of laparotomy in a staged approach for resolution of bilateral or complicated perineal hernia in 41 dogs. Vet Surg 2004;33:412-421.
32. Yoon H, Mann FA, Clinical evaluation of three different colopexy techniques in dogs. Indian Vet J 2009; 86:1129-1131.
33. Welches CD, Scavelli TD, Aronsohn MG, et al. Perineal hernia in the cat: a retrospective study of 40 cases. J Am Anim Hosp Assoc 1992;28:431-438.
34. Johnson MS, Gourley IM. Perineal hernia in a cat. Vet Med 1980;75:241-243.
35. Ashton DG. Perineal hernia in the cat: a description of two cases. J Small Anim Pract 1976;17:473-477.
36. Leighton RL. Perineal hernia in a cat. Feline Pract 1979;9:44.
37. Anderson M, Pope ER, Constantinescu GM. Perineal hernia in a cougar. J Am Vet Med Assoc 1992;201:1771-1772.
38. Martin WD, Fletcher TF, Bradley WE. Perineal musculature in the cat. Anat Rec 1974;180:3-14.
39. Constantinescu GM, Amann JF, Anderson MA, et al. Topography and surgery in the regio perinealis of the cat. Wien Tierarztl Monatsschr 1993;80:208-211.
40. Babic DV, Stejskal M, Capak D, et al. Application of a semitendinosus muscle flap in the treatment of perineal hernia in a cat. Vet Rec 2005;156:182-184.
     

Introduction

Prepubic hernia or cranial pubic ligament (CPL) rupture is the most common abdominal hernia caused by blunt trauma (particularly vehicular trauma) in small animals.^1,2 The lateral paralumbar (flank) region hernia is also seen with some frequency after blunt trauma presumably because it is another area that lacks elasticity, and it is not supported by the rectus abdominis muscle.³ Because of their close anatomic relationship, many patients with prepubic hernias have coexisting inguinal ligament rupture and organs such as the bladder and/or intestines may be found within the hernia. These organs may extend into the inguinal canal or femoral vascular lacunae area causing swelling reaching from the caudal-ventral abdominal wall into the medial thigh and flank (Figure 38-25). One case report described a rare bladder incarceration within a chronic prepubic hernia in a dog with a vesicular-cutaneous fistula.⁴

The CPL attaches to the cranial aspect of the pubis and extends from one iliopectineal eminence and pectineus muscle to the other (See Figure 38-25). It serves as the principal attachment of the rectus abdominis muscle to the pelvis and is under constant tension. Blunt trauma causes avulsion of the cranial pubic ligament from its boney attachment or, less commonly, a tear occurs at the musculotendinous junction. In contrast, CPL rupture is spontaneous in large animals, and most often occurs during the last two months of gestation apparently due to increasing uterine weight.⁵

Blunt trauma severe enough to cause rupture of the abdominal wall may also cause widespread crush, rupture, or avulsion damage to surrounding structures and intra-abdominal organs. As many as 75% of small animals with traumatic abdominal hernias have other serious injuries, most are orthopedic in nature usually involving the pelvis. Other important common injuries are to soft tissues, including respiratory, gastrointestinal, and genitourinary systems.^2,3 Following patient stabilization, a thorough physical examination and diagnostic workup are indicated to evaluate for more insidious, often life-threatening, injuries.
 

The diagnosis of prepubic hernia is often confirmed by palpating a defect in the caudal abdominal wall, by reduction of tissue back into the caudal abdomen, or by palpation of organs in the subcutaneous space near the pubic or thigh areas. Organs such as the intestine may not be confined to the local area and may migrate a considerable distance from the hernia, such as down the medial thigh or along the abdominal wall and thorax. Pain and swelling from trauma or hemorrhage may not allow detection of a hernial ring or herniated tissue during physical examination. In these instances, abdominal radiographs or ultrasound of the local area are indicated. Routine ventral-dorsal and lateral radiographs aid in identifying the abdominal stripe, or lack thereof, any malposition of the abdominal contents, and the presence of fluid in the abdomen. When radiographs or ultrasound are not conclusive, a positive contrast peritoneogram may help to delineate the abdominal wall defect. Patients should be thoroughly evaluated for concurrent injuries such as urinary tract rupture, abdominal hemorrhage, fractures, and thoracic trauma. Survey thoracic and abdominal films (including the pelvic area), and blood workup are usually indicated for all severely traumatized patients. If electrocardiography is available, a rhythm strip should be evaluated, otherwise, detection of an irregular rhythm or dropped beats while examining the pulse may indicate traumatic myocarditis. A complete blood count and serum chemistries should be evaluated to determine if significant blood loss or organ compromise has occurred.

Stabilization of the patient’s condition takes precedence over hernia repair. Because these hernias are usually large, the risk of incarceration or strangulation of viscera is low. Therefore, if the patient is stable and serious intra-abdominal trauma has been ruled out, the hernia can be repaired several days later, after swelling and hemorrhage begins to subside and tissues reestablish their blood supply. If the patient does not stabilize with resuscitative measures, serious intra-abdominal injury or contamination should be suspected and further diagnostic tests and/or emergency exploratory laparotomy may be indicated.

Surgical Technique

Surgical correction is usually performed through a ventral midline approach. When an exploratory laparotomy is indicated, the entire abdomen should be prepared aseptically, and if the hernial sac extends to adjacent areas, these areas should be liberally prepared also. The way in which the patient is positioned on the operating table may be critical for successful closure of a prepubic hernia. Closure may be virtually impossible if the patient is placed in a routine dorsal recumbent position (limbs pulled caudally and abducted and trunk in slight dorsal flexion (Figure 38-26A). The rear limbs should be pulled cranially and the body ventroflexed to relieve tension during hernia repair (Figure 38-26B). If transposition of the cranial sartorius muscle is planned to augment the primary hernia repair, the adjacent hind limb is also prepared for aseptic surgery (Figure 38-27). Prophylactic antibiotics are administered during preparation of the surgical site.
 

Due to serious concurrent soft tissue injuries related to acute traumatic abdominal hernias, the abdomen should be aseptically prepared for thorough exploration before efforts are made at hernia repair.³ In dogs surviving the acute insult that develop a chronic prepubic hernia, the defect can be safely approached locally without abdominal exploration. When prepubic hernias become chronic, significant muscle contraction and loss of tissue elasticity occurs, exerting excessive tension on the repair. In some cases, it is impossible to appose tissues. If tension is difficult to overcome, muscle or tendon has been lost, or the defect is very large, the use of a mesh prosthesis is recommended.⁶ Besides hernia recurrence, wound infection, seroma, and skin slough are the most common complications after repair.⁶ Traumatized skin and soft tissues are handled with utmost care, and excessive blunt dissection is avoided because the vascular supply may be tenuous and further insult could result in tissue loss or an increased risk of infection.⁶ After abdominal exploration, and necessary organ repair is completed, the abdominal cavity is lavaged, and the linea alba is closed routinely.

The prepubic hernia is exposed by careful dissection and debridement of devitalized tissue (Figure 38-28). Excision of connective tissue surrounding the hernia is avoided unless it is devitalized or infected, and will not support sutures. The surgeon carefully inspects the lateral margins to determine whether the hernia extends into the inguinal and femoral areas. Important vascular and neural structures are isolated and protected, particularly if the femoral region requires reconstruction. If femoral or inguinal areas are involved, the regional anatomy is studied carefully before undertaking herniorrhapy. The prepubic hernia component is repaired first, to help align tissues correctly for anatomic reconstruction of the inguinal and femoral hernias, if present. The cranial public ligament is reattached with large 2-0 to 0 size monofilament (prolonged absorbable) suture or nonabsorbable suture. If enough healthy tendon is present, the surgeon anatomically repairs the hernia with preplaced interrupted sutures incorporating large bites of tissue. As adjacent preplaced sutures are pulled firmly, knot the individual sutures. This maneuver helps reduce the risk of suture cutout during repair. In most prepubic hernias, the ligament is avulsed from the pubic bone leaving scant soft tissue attached. In this case, holes are drilled in the cranial brim of the pubis to anchor sutures. When the hernia cannot be repaired without excess tension, a cuff mesh reinforcement of the prepubic tendon can be performed using polypropylene mesh (Figure 38-29). Concurrent femoral or inguinal hernias are repaired by carefully isolating the hernia edges and anatomic reconstruction. Often, the inguinal ligament is ruptured, and sutures are preplaced between the abdominal oblique fascia and the musculature of the proximal medial thigh. Extreme care is required to avoid damaging, incorporating or obstructing important vascular and neural structures of the inguinal or femoral canal. If mesh is used for reconstruction, I prefer to transpose the cranial sartorius muscle to provide a seal and bring additional blood supply over the repair to support rapid healing and incorporation of the mesh (See Figure 38-27).^7,8 I also consider using this muscle to augment inguinal or femoral defects when tissue edges are tenuous or when the wound will not support synthetic mesh (heavily contaminated wounds). The surgeon should recognize that this muscle is not covered by heavy fascia so the muscle alone should not be expected to maintain abdominal wall continuity under excessive tension.

Usually a large amount of dead space is present in the subcutaneous tissues after herniorrhaphy. Gravity dependent drains such as Penrose drains or, preferably, closed suction drain systems (Jackson-Pratt) should be used in most cases. Avoid placing open-drain systems directly against buried mesh to reduce the risk of ascending infection.
 

Postoperative Care

Monitoring and postoperative care instructions are dictated by the nature and severity of the injury. The surgeon should continue to monitor the patient’s vital signs and remains aware of possible problems related to occult visceral damage. Patients should be given analgesic agents for at least 24 hours after the surgical procedure. An epidural using narcotic analgesics is very effective to prevent postoperative pain. Unless contraindicated, nonsteroidal anti-inflammatory drugs are also administered to reduce postoperative wound edema and pain. Wounds and drains should be monitored for signs of infection or hernia recurrence. Drains should be bandaged, if possible, and removed when discharge has diminished. This is usually possible within 3 days. If infection occurs, wounds are opened, cultured, debrided, and secondarily closed. Strict exercise limitation is recommended for at least four to six weeks particularly if a prosthetic mesh was implanted. If the inguinal or femoral areas have been reconstructed along with the prepubic hernia, the surgeon should consider placing the patient’s hind limbs in hobbles to prevent tension from excess limb abduction. An Elizabethan collar is used to guard against premature drain removal or wound mutilation.

Prognosis

Based on a report of a series of patients undergoing prepubic herniorrhaphy, approximately 80% will survive and have successful hernia repair. If a hernia recurs (about 15% do) the defect is usually evident by one month after surgery. Repair of these recurrent hernias is usually successful provided the repair is anatomic, is free of tension, and incorporates strong tissue. The remaining 20% have poor results because of the severity of accompanying injuries.^1,3

References

1. Mann FA et al.: Cranial pubic ligament rupture in dogs and cats. J Am Anim Hosp Assoc 22:519, 1986.
2. Waldron DR et al.: Abdominal hernias in dogs and cats: A review of 24 cases. J Am Anim Hosp Assoc 22:818, 1986.
3. Shaw SP, Rozanski EA, Rush JE: Traumatic body wall herniation in 36 dogs and cats. J Am Anim Hosp Assoc 39:35-46, 2003.
4. Green RB, Quigg JA, Holt PE: Vesicocutaneous fistulation following prepubic tendon rupture in a bitch. J Small Anim Pract 30:315-317, 1989.
5. Hanson RR, Todhunter RJ. Herniation of the abdominal wall in pregnant mares. J Am Vet Med Assoc 189:790-3, 1986.
6. Smeak DD: Management and prevention of surgical complications associated with small animal abdominal herniorrhaphy. Prob Vet Med 1:254, 1989.
7. Weinstein MJ, Pavletic MM, Boudrieau RJ, Engler SJ: Cranial sartorius muscle flap in the dog. Vet Surg 184:286-291, 1989.
8. Philiber D, Fowler JD: Use of muscle flaps in reconstructive surgery. Comp Contin Ed Pract Vet 18:395-405, 1996.