(Rectal sacculation next to the anus)
Perianal Hernia is the separation of perineal (next to the anus) muscles and the maculation or herniation of the rectum and/or abdominal contents under the skin causing visible bulging. Most PAHs are adjacent to the anus but can be above or below it. The condition often involves both sides, therefor is considered bilateral. The breakdown of the pelvic muscles allows fecal impaction in the hernia and results in difficult bowel movements and straining. The cause of perineal hernias is associated with male hormones, enlarged prostate gland, straining and muscle weakness. It is a rare occurrence in female dogs because their pelvic muscles are stronger than males and NOT having a prostate gland eliminates this as an underlying cause. Any condition that causes straining may stress the pelvic muscles to a point of separation. The list of conditions includes: prostate enlargement, cystitis, urinary tract obstruction, rectal obstruction, constipation, anal sac disease and diarrhea.
The condition of perineal hernia (PAH) is an anatomical failure and, with fecal impaction, worsens with time. Early detection and neutering may avoid the need for surgery, but in most cases the muscle separation and weakness has progressed to a point of needing surgery. Once diagnosed, early surgical correction is recommended to ALWAYS include neutering with hopes that surgery will only be needed on one side. This condition can become an emergency if the bladder herniates and becomes obstructed.
Most dogs are mature and over the age of 5 years at onset. The breeds most commonly represented are Boston terriers, dachshunds, Welch corgis, poodles, Old English sheepdogs and mixed breeds. Most patients present for examination with straining, difficult defecation, and visible bulging of the anal area.
Coupled with the presenting history and clinical signs, rectal exam is critical for diagnosing a PAH. Not all dogs will present with swelling and the presence of tumor in the area can be mistaken for a hernia. Rectal exam (usual done awake) can determine the presence of weakness and separation of the pelvic muscles. The rectal exam can determine the severity of the hernia and the contents in the area. Right sided hernias do appear to be more frequent. Radiographs (x-rays) are helpful in the diagnosis especially in identifying the contents and severity of the impaction. In some cases an ultrasound will be indicated to further identify prostate and bladder. The main differential diagnoses include tumors, anal sac swelling and abscess, rectal impaction and rectal prolapse.
Medical and Surgical Management
Most medical treatment is aimed at softening the stool and preventing straining. Urinary tract infections and prostatitis should be corrected. Stool softeners, laxatives and enemas can relieve the obstruction, but not correct the condition, along with frequent manual exams to remove impacted fecal material. Long-term use of these treatments is usually palliative and temporary, and surgical correction is warranted.
Surgical repair of the hernia and stabilization of the pelvic muscles along with castration is usually recommended, especially if more than just a swelling and rectum are herniated, i.e.bladder/bowel. The main goal of castration is to shrink the prostate by removal of testosterone and to hopefully prevent recurrence (noncastrated males have almost a 3 times greater recurrence rate). At the VSRP, our policy is to always do castration with hernia repair. The two techniques for hernia repair are (1) conventional, traditional reapposition of the muscle, and (2) transposition of the muscle flap called the internal obturator muscle. The internal obturator flap technique is a more natural anatomical repair of the defect and is the technique of choice and has less chance of recurrence. It provides a new “shelf” for the rectum to sit against in its more normal position. Plus the first technique, which attempts to reappose the weakened muscles, lacks the same strength of repair since these muscles have been stretched out already. Immediate postoperative rectal exam with the internal muscle transposition technique usually indicates a stronger support for the rectum. Bilateral hernia repair is performed if both sides are affected at the same time to prevent straining against an unoperated side. Postoperatively, the stool needs to be maintained soft-formed with the use of stool softeners and Metamucil as needed. Prevention of postoperative straining is critical. Often, because the rectum has been so stretched out by the hernia, a rectal prolapse can occur and should be gently manually reduced until it contracts. This can take a few days. The surgical site needs to be cleaned and warm compressed daily. An e-collar is normally needed to prevent licking and no scooting should be allowed. Antibiotics and pain relief is given for the first 5 – 7 days after surgery.
Given the application of good surgical technique and patient selection and preparation, the prognosis is good. Recurrence and opposite side herniation are the two most common complications. Castration is a major factor in preventing both complications. It is important to prevent future straining and the owner should be very aware of the patient’s bowel movement habits.