These hernias differ from other hernias in that the displaced organs are not usually within a peritoneal sac.
These hernias differ from other hernias in that the displaced organs are not usually within a peritoneal sac. A specific cause has not yet been established for perineal hernias and multiple causative agents are most likely. It has been attributed to failure or weakening of the fascia and muscles of the perineum, permitting abdominal or pelvic organs to prolapse into the space created by atrophy or injury of the pelvic diaphragm.Although perineal hernias have been reported in the bitch, it occurs most commonly in intact male dogs over 8 years old, It does, however, occur in young animals, A structural predisposition has been suggested and dogs with rudimentary tails such as Boston Terriers would be more susceptible. Also reported is a hormonal imbalance etiology. This theory is supported by evidence that some dogs with perineal hernia are concurrently afflicted with testicular tumors, prostatic enlargement or enlargement of a cystic uterus musculinea.
Constipation has been cited as a factor in perineal hernia but this has not been firmly established as a cause but more often a result of prostatic enlargement.
Most patients are presented for examination because they have been observed straining to defecate. Also, a swelling lateral to and extending from some distance ventral to the anus is a common sign. The hernial swelling is soft and fluctuate and manipulation often results in reduction of contents. If the bladder and prostate are hernial contents then the swelling may be turgid. if the bladder has become incarcerated or strangulated due to distension with urine following herniation, reduction might only be possible by withdrawing urine from the bladder. A perineal hernia may be bilateral, in which case the whole perineal region is swollen and the anus is displaced caudally.
A hernia is apparent when the contents of the swelling can be pushed back into the pelvic cavity. This may be facilitated by elevating the animal's hindlimbs. Simultaneous palpation of the perineal enlargement and rectal examination aids in determining whether there is continuity between the swelling and peritoneal cavity, Digital examination of the rectum often reveals a lateral deviation or diverticulum into the hernial area. This deviation results in accumulation of feces in the rectum, and causes the animal to strain. During the course of the examination, the feces can be removed from the diverticulum, It then will be possible to pass the finger into it and observe its movement under the skin.
Affected patients may only display the usual signs of discomfort, but if the bladder becomes strangulated and distended with urine following herniation, the swelling may be greatly enlarged and the overlying skin may be tense, blue-red, and exude serum. It may or may not be possible to catheterize the bladder in this case. The diagnosis of bilateral hernia sometimes is difficult because its reduction is not easy. A large unilateral hernia may migrate ventral to the anus into the opposite side and appear to be bilateral.
Most cases of perineal hernia are not emergency cases. However, those with acute complications, such as retroflexion of the bladder and inability to urinate, must be treated as emergencies.
Relief can often be obtained by passing a catheter into the bladder. if this is not possible, urine can be removed by performing paracentesis. A 20 gauge needle or smaller is adequate. Once the bladder is emptied, an attempt can be made to reduce the hernia. When the hernial contents have been reduced, the animal should be given a narcotic to minimize straining. Such patients are suitable candidates for surgery in 24 hours. Once the diagnosis has been established surgery should not be delayed. if surgery is delayed the patient should be fed a low-residue diet for 48 hours prior to surgery. The feces are then soft in consistency and the danger of post-operative wound disruption is reduced, Recurrence of perineal hernia is not common and has been reported to recur in two to forty percent of the cases.
The hernial funnel extends from the pelvic cavity to the hernial sac lateral to the anus. The hernia is limited ventrally and laterally by the walls of the pelvis and medially by the rectum.
The levator ani is a thin fan-shaped muscle that arises from the pelvic surface of the ischium and pubis at the pelvis symphysis, the cranial border of the pubis and the pelvic surface of the shaft of the ilium. It is inserted on the external anal sphincter and caudal vertebrae. The two muscles together with their fascial layers form the pelvic diaphragm through which the genitourinary and digestive tracts open to the outside, When these muscles separate, relax, or become atrophic, the abdominal or pelvic organs may push through the defect. The hernia occurs between the external anal sphincter and the levator ani muscles. if the perineal fascia which surrounds the anus and is confluent with the gluteal fascia stretches or ruptures, the hernial contents prolapse lateral to the anus and are confined only by the skin.
A purse-string suture is placed around the anus to prevent defecation during the operation. It is best to place the patient on its sternum and elevate the hindquarters. The tail is pulled forward and laterally to expose the perineal region. The operation is designed to reconstruct the pelvic diaphragm. Complete reconstruction may not be possible due to tearing or atrophy of muscle; closure of the hernial funnel and obliteration of space may be all that can be accomplished.
A half circle skin incision is made over the hernia and extended an adequate distance above and below the hernia to facilitate manipulation of the tissues. Frequently there will be no evidence of fascia and fibrous tissue, and the muscles will be atrophied and intermingled with omentum-like, necrotic, fatty tissue, The tissue strands must be disrupted between muscle layers and the fatty tissue ligated and removed as necessary. The area is likely to be hemorrhagic and blood serum escapes when the hernial sac is entered.
The herniated organs are replaced into the pelvic cavity by gentle manipulation and then a clear view of the funnel is obtained. On the medial side is the rectum, terminating at the anal sphincter. This usually is the only structure on the medial side into which sutures can be inserted. The muscular structures on the lateral side of the funnel are not easily seen but may be identified by palpation. The levator ani and coccygeous muscle are on the dorsolateral surface of the funnel, 2-0 Stainless steel wire suture is inserted through these muscles and into the dorsal part of the anal sphincter. The internal obturator muscle is also sutured to the ventrolateral aspect of the rectum,
Immediately below these sutures, additional ones are inserted between the anal sphincter and sacrotuberous ligament. This ligament is a fairly broad band that can be identified by passing the finger along the medial wall of the pelvis and hooking the finger backward. The ligament may be mistaken for bone. The lower portion of the opening is closed by inserting a series of sutures through the internal obturator muscle which lies on the floor of the pelvis, and the ventral surface of the anal sphincter. This is difficult because the structures lie deeply within the pelvis and careful manipulation is necessary.
When inserting the lower sutures between the head of the internal obturator muscle and ventral portion of the anal sphincter, care must be taken to avoid injuring the blood and nerve supply to the anus, The muscles of the anal sphincter are supplied by anal branches of the pudendal nerve and by the perineal arteries and satellite veins, These structures will be encountered in a band along the ventral aspect of the rectum. Injury to the nerve might result in fecal incontinence.
The sutures should not be tied until all have been inserted,' otherwise increasing difficulty will be encountered in placing the sutures. Following closure of the initial suture line an attempt is made to locate intact perineal fascia that may have retracted laterally. The edge of the fascia is grasped with an Allis forceps and a flap is formed by dissecting the outer surface of the fascia away from the overlying skin, The fascia flap is pulled medially and sutured to the most caudal portion of the anal sphincter. Another series of sutures is inserted in the subcutaneous tissues and excessive skin is trimmed to assure adequate and accurate closure.
Possible complications following repair of a perineal hernia include fecal and urinary incontinence, wound infection from fecal contamination and lameness resulting from damage to the sciatic nerve during surgery. In severe cases, nylon mesh may be used to form a "diaphragm" that prevents the caudal displacement of the viscera.
Routine prophylactic chemotherapy is advisable and a low residue diet should be fed to prevent excessive straining during defecation, In most cases recurrence is not a problem. Both sides of a bilateral hernia should not be operated at the same time since this would put too much stress on the external anal sphincter. A 4 to 6 week lag should occur between surgeries, unless a newer obturator lift method is employed.
The approach to this surgery is identical to traditional repair, and after exposure herniated organs are retropulsed back into the abdomen. Identification of the external anal sphincter, sacrotuberous ligament and the internal obturator is severed at the point that it passes laterally over the body of the ischium, The muscle is then brought dorsally to fill the defect left by the hernia, Initial suture is placed between the lateral aspect of the external anal sphincter and the sacrotuberous ligament and gluteal fascia as far dorsal as possible in order to create a bed for the apex of the internal obturator is sutured to the caudomedial edge of the sacrotuberous ligament with 4 - 6 size 0 PDS sutures in a cruciate pattern. The caudomedial border of the internal obturator is likewise sutured to the external anal sphincter. Replacement of all sutures before knot's are thrown facilitates the task. Layered subcutaneous closure is accomplished with gut to obliterate dead space Skin obscure is routine.