Abdominal Hernia

Perineal hernias develop when the pelvic diaphragm muscles weaken significantly or fail completely. The pelvic diaphragm is formed by multiple muscles that work together to support the rectum and prevent abdominal contents from moving into the ischiorectal fossa. The most frequent form occurs between the levator ani, internal obturator, and external anal sphincter muscles and is called a caudal perineal hernia. Other forms include:

• dorsolateral (between the coccygeus and levator ani)
• ventral (between the ischiourethralis, bulbocavernosus, and ischiocavernosus muscles)
• sciatic perineal hernia (between the coccygeus and the sacrotuberous ligament)

More than one type can occur on the same side, and hernias may also be present on the opposite (contralateral) side. Because of this muscular weakness, retroperitoneal fat, omentum, or abdominal organs may protrude into the ischiorectal fossa, creating a visible perineal bulge. Affected pets may show swelling next to the rectum on one or both sides, along with constipation, difficult defecation, lethargy, difficulty urinating, and abnormal tail position/carriage.

This condition mainly affects older animals, most often 7–9 years of age. The precise cause of pelvic diaphragm weakening or failure is not clearly established. Several theories exist, potentially acting alone or together. Since intact (non-castrated) male dogs and cats are predisposed, and because castration performed at the time of repair appears to lower recurrence risk, androgens are considered an important contributing factor. Additional contributors may include inherent structural weakness of the pelvic diaphragm, neurologic injury to the nerves supplying the pelvic muscles, or concurrent abdominal disease that leads to chronic straining.

Figure 1. A large perineal hernia in a dog
Pets with perineal hernias usually have a swelling beside the anus on one or both sides (Figure 1). The swelling can contain displaced abdominal or pelvic canal structures such as retroperitoneal fat, omentum, an enlarged rectum, the prostate, the urinary bladder, and small intestine. Clinical signs depend on which organs are trapped in the hernia. Common signs include:

• constipation
• straining to defecate
• straining to urinate
• inability to urinate
• urinary incontinence
• abdominal pain
• lethargy
• depression
• anorexia
• altered tail carriage

Figure 2. Radiograph of a dog with a perineal hernia
Diagnosis relies on a careful rectal examination. This helps assess whether a mass-like lesion is present, evaluate for prostate disease, identify what is in the hernia, and determine whether the condition is unilateral or bilateral. Some pets require pain control or sedation to allow a complete rectal exam. After confirming a perineal hernia, a thorough metabolic and abdominal evaluation should follow. Your primary care veterinarian will commonly recommend:

• complete blood count (CBC)
• biochemical profile
• urinalysis

These tests help detect concurrent systemic illness. Advanced imaging—such as ultrasound and abdominal radiographs—may be recommended to clarify hernia contents, urinary bladder size and position, colon size and position, prostate disease, or the presence of cancer (Figure 2).

Any pet with swelling next to the rectum plus the clinical signs listed above should receive veterinary evaluation promptly. Entrapment of organs in a perineal hernia can be life-threatening and may require emergency stabilization before definitive surgery. Your veterinarian may refer you to an ACVS board-certified veterinary surgeon for repair.

Perineal hernias alone can cause constipation, and constipation can in turn impair colonic motility. They can also interfere with urination. In some cases, severe straining causes the bladder to retroflex (flip backward into the pelvic canal), leading to urinary obstruction and possibly reduced blood supply to the bladder. If a loop of intestine becomes trapped, severe pain and compromised blood supply can occur. Emergency surgery is indicated for pets with abdominal pain, inability to urinate, or a strangulated loop of small intestine.

For non-emergency cases, management may be medical or elective surgical. Medical therapy is mainly used to prepare a pet for surgery and is usually not effective as a permanent solution. Medical management typically includes enemas, stool softeners, intravenous fluids, dietary strategies, and analgesics.

Surgery is intended to reconstruct the pelvic diaphragm and reduce recurrence risk. A perineal herniorrhaphy generally involves suturing tissues to restore normal pelvic diaphragm anatomy. Adding a muscle flap can reinforce the repair. The internal obturator muscle—located along the pelvic floor—is the flap most commonly used. In severe cases, other nearby muscles such as the superficial gluteal or semitendinosus may be used. Surgical mesh may also be placed when a defect remains despite anatomical reconstruction and muscle transposition. Recent studies also suggest that some pets presenting with a one-sided hernia may have a subtle hernia on the opposite side; therefore, the surgeon may advise contralateral repair as well.

Additional procedures may include an organopexy, where sutures permanently anchor an organ to the adjacent abdominal wall to reduce the chance of retroflexion into the ischiorectal fossa. This may involve:

• colon (colopexy)
• bladder (cystopexy)
• vas deferens (vas deferensopexy)

Organopexy is particularly considered when these organs have already herniated into the ischiorectal fossa or when a pet has recurrent perineal hernias.

Castration is recommended for all pets at the time of surgery to help reduce recurrence risk.

During the initial hospital period, pets are monitored for complications. Many issues are minor and do not require another procedure. Examples include incision infection (the incision is close to the anus), wound dehiscence, bruising, temporary pain with defecation, an urgent need to defecate without producing stool, and swelling around the surgical site. With time and appropriate medical treatment, these signs usually improve over days to weeks. Other possible problems include fecal incontinence or urinary tract complications, especially if the bladder was trapped.

Complications that may require revision surgery include nerve entrapment and recurrence. Nerve entrapment is often recognized immediately after surgery because affected pets are markedly painful and may show hindlimb weakness or neurologic deficits. Recurrence can occur even with strong surgical technique, with reported recurrence rates ranging from 10–50%, depending on the repair methods used.

In straightforward cases, recovery is typically about 2 weeks. If complications occur, your surgeon will discuss appropriate next steps.