Perineal Hernia

Basics

Overview

The term Perineal hernia refers to a spectrum of diseases in which the perineal diaphragm is weakened or ruptured, resulting in abnormal function during defecation and progressing to herniation of pelvic and abdominal viscera.
Weakening of the perineal diaphragm is postulated to result from hormonal influences on the perineal musculature in male dogs, but may also follow from conditions causing chronic and excessive straining, or neuropathic weakness of the perineal muscles.
Separation of the perineal muscles (levator ani and coccygeus) from the anal sphincter and rectum allows lateral bulging of the rectum when the animal strains, thereby preventing coordinated defecation. Separation of the muscles also allows pelvic and abdominal viscera to migrate caudally.
Retroflexion of the bladder may occur, and the subsequent incarceration may lead to ureteral or urethral obstruction. Strangulation of herniated viscera may occur in the severest cases.

Signalment

This disease is seen most commonly in dogs, but also sporadically in cats.
Older, intact male dogs are most at risk, however it can occur in females.

Signs

Straining to defecate or urinate.
Constipation is the main feature, although some patients present for supposed diarrhea, when liquid feces escapes around the firmer stool.
Unilateral or bilateral perineal bulge due to fecal impaction and/or herniation: this is often the only presenting sign in cats.

Causes & Risk Factors

Intact status in older male dogs.
Underlying pathology leading to excessive straining: prostatomegaly in male dogs, while megacolon and malunion of pelvic fractures can predispose to perineal laxity in cats.
Caudal neuropathy, malformation or injury such as tail traction.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

Other conditions leading to obstipation and straining. Perineal neoplasia (adenoma, adenocarcinoma), sub-lumbar lymphadenomegaly secondary to anal sac adenocarcinoma, rectal tumor, perineal lipoma, paraprostatic cyst. Perineal abscess (anal sac abscess, foreign body).

CBC/Biochemistry/Urinalysis

No specific abnormalities on blood work, except azotemia and elevated creatinine if urinary obstruction occurs.

Imaging

Abdominal radiography: confirm constipation, prostatomegaly, sublumbar lymphadenomegaly, megacolon in cats.
Pelvic radiography: confirm pelvic fracture malunion or intrapelvic mass.
Abdominal ultrasonography: evaluate the size and consistency of the prostate.
Perineal ultrasonography: evaluate presence of viscera or mass lessions.

Diagnostic Procedures

Thorough rectal palpation should confirm accumulation of feces in the dilated rectum, and perineal laxity.
Insert a finger into the rectum and hook it laterally. If it is possible to pinch the rectal mucosa and skin together between the tip of the forefinger and thumb, without palpating a muscle shelf in between, the integrity of the pelvic diaphragm has been compromised.
It is important to thoroughly evaluate both sides of the perineum: bilateral perineal laxity is often present even when herniation has only occurred on one side. Also evaluate the position of the anal sphincter in relation to the tuber ischii.
In a normal patient, the sphincter is held in position dorsal and slightly cranial to the caudal extent of the tuber ischii. When the perineal diaphragm breaks down, the anus migrates caudally.
Endoscopy or fine-needle aspiration biopsy may be indicated if a mass lesion is present extra or intraluminally.

Treatment ⬆ ⬇

Treatment

Low residue diet and fecal softeners may ameliorate clinical signs temporarily, but surgical repair of the perineal diaphragm is required for definitive treatment.
Castration of male dogs should always be performed simultaneously with herniorrhaphy in male dogs, due to the high rate of recurrence in intact dogs.
Bladder retroflexion is considered an emergency; either due to urinary obstruction or the potential for strangulation and devitalization. In these patients, the urethra should be catheterized and the bladder decompressed if possible.
In some cases, percutaneous cystocentesis is required to decompress and reposition the bladder before a urethral catheter can be passed.
A balanced electrolyte solution should be administered intravenously prior to and during surgery in patients suffering from azotemia and hyperkalemia following urinary obstruction.
Prior to surgical correction, impacted feces should be gently removed from the rectum. Enemas are not recommended as liquid feces may not be completely evacuated, leading to more contamination during surgery.
Intraoperative antibiotics may be given, but there is no indication to continue antibiotic treatment postoperatively.
The anal sacs are expressed and flushed, and a purse-string suture placed at the anocutaneous junction. The entire perineum and tail base is clipped, with the clip extending cranially past the greater trochanter of the femur on each side.
In intact male dogs, the scrotum and surrounding skin is prepped for either a prescrotal or caudal castration approach. Depending on the preferred approach, the dog is castrated in dorsal recumbency and then flipped and placed in a perineal stand for the hernia repair, or placed in the perineal stand and castration performed via a caudal approach to the scrotum.
A curvilinear incision is made 1–2 cm lateral to the anus, extending from the ventral tail base to the tuber ischium. The subcutaneous tissues are dissected in order to expose the hernia sac. This sac is perforated, at which point a small amount of serosanguinous fluid is usually encountered.
Omentum is the most common organ within the hernia, and it may contain organizing hematomas or areas of saponification: these can be resected if necessary. The loose connective tissue is dissected to expose the coccygeus muscle (lateral), the anal sphincter (medial) and the internal obturator (ventral).
Take care to avoid damaging the pudendal nerve and artery as it crosses the dorsal aspect of the internal obturator toward the anus. Most surgeons prefer to elevate the internal obturator from the ischium in order to close the hernia ring with minimal tension.
Three simple interrupted sutures (nonabsorbable or long-acting absorbable, appropriately spaced) are placed between the following muscles: dorsal anal sphincter and dorsal coccygeus, ventral anal sphincter and medial internal obturator, ventral coccygeus and lateral internal obturator. The surgical wounds are then closed routinely. Ensure that the purse-string suture is removed&excl
It may be helpful in large dogs with large bilateral hernias, especially if bladder retroflexion with urinary obstruction has occurred, to initially perform exploratory celiotomy, reposition the bladder and colon, and perform incisional colopexy and cystopexy.
Staging the procedure, so that herniorrhaphy can be performed a few days later, when the patient's condition has stabilized and the perineal edema has resolved, may facilitate definitive hernia repair.
This technique has not been shown to affect recurrence rates, but does simplify the definitive herniorrhaphy by allowing local edema to settle, and reducing the tendency of abdominal contents to migrate into the field during surgical correction.
In patients with very poor perineal muscle development, the repair may be supported by using a flap from the superficial gluteal muscle, incorporating prosthetic mesh into the repair, or in very severe cases, elevating and rotating the semitendinosus muscle. A superficial gluteal muscle flap is recommended in cats and very small dogs.
The incisions are iced postoperatively to reduce pain and swelling. An Elizabethan collar is placed to prevent self-trauma to the incisions and appropriate analgesia given. A moist, low-residue diet is usually sufficient to maintain sufficiently soft stool to prevent straining or constipation postoperatively. Fecal softeners may be administered, but may lead to diarrhea and fecal soiling in the first days after surgery, especially if a bilateral repair has been performed. The patient's activity should be restricted for at least 3–4 weeks after surgery.
The main risks of perineal herniorrhaphy are recurrence (greatly reduced by castration and use of internal obturator flap), and temporary dysfunction of the anal sphincter due to stretching following bilateral herniorrhaphy.
Fecal and urinary incontinence can occur if excessive dissection around the pudendal nerve or peritoneal reflections are performed.

Medications ⬆ ⬇

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

The patient should be evaluated thoroughly for the first 48 hours following surgery, with particular attention paid to urination and defecation. A rectal examination should be performed at the time of suture removal if feasible.

Prevention/Avoidance

The major factor known to reduce the risk of recurrence following surgery is castration.

Possible Complications

Constipation and bladder retroflexion/obstruction if left untreated.

Expected Course and Prognosis

Recovery and function following surgery is usually excellent. There is a 10–50% risk of recurrence depending on presence of underlying conditions, surgical approach, and intact status of the dog.

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Basics ⬇

Diagnosis ⬆ ⬇

Treatment ⬆ ⬇

Medications ⬆ ⬇

Follow-Up ⬆ ⬇

Miscellaneous ⬆