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A perineal hernia is a bulge that forms beside the anus when the muscles of the pelvic floor give way. Those muscles, which include the levator ani and coccygeus, normally hold the rectum, bladder, prostate, and pelvic fat in place. When they weaken or tear, tissue slides through the gap and collects under the skin next to the tail. The Merck Veterinary Manual explains that the hernia results from failure of those muscles, allowing pelvic or abdominal contents to push into the perineum. Most owners notice it first as a soft swelling on one side of the anus, paired with a dog that strains to pass stool, produces only small amounts, or seems constipated despite a good diet and plenty of water. The swelling may shrink when the dog rests and grow again after straining, and in some dogs both sides are affected, though one side is usually worse and noticed first by the family at home. Because the rectum loses its support, it can bend into the pouch and form a pocket where stool collects instead of passing normally each day.
This is mostly a disease of middle aged to older male dogs that have not been neutered, and it rarely fixes itself. The pouch beside the rectum traps stool, so each attempt to defecate becomes harder, and straining in turn stretches the weak area further. In the more dangerous version, the bladder slips into the hernia and twists so urine cannot leave the body, which turns a slow problem into an emergency within hours. Loops of intestine can also become trapped and lose their blood supply. Even without those crises, daily straining, discomfort, and soiling wear a dog down and make simple routines miserable. Surgery to rebuild the pelvic floor is the standard answer, and planning it before an emergency, while your dog is comfortable and stable, gives the repair its best chance of holding. A prompt exam also lets your vet check the prostate and plan neutering, which supports the repair.
The pelvic floor muscles weaken gradually in most cases, and the exact reason is not fully understood. Hormones appear to play a central role, because the condition is so strongly tied to unneutered males, and an enlarged prostate linked to hormone balance has been implicated as well. Anything that makes a dog strain again and again adds load to those muscles: chronic constipation, prostate disease that narrows the passage of stool or urine, and long standing coughing may all contribute. Breed predisposition, nerve damage in the area, and direct trauma can also play a part. The Merck Veterinary Manual lists breed predisposition, hormonal imbalance, prostatic disease, chronic constipation, and weakness from chronic straining among the factors involved.
Breeds and dogs at higher risk: Middle aged to older unneutered male dogs are affected far more than any other group, and the condition is rare in females. The Merck Veterinary Manual reports predispositions in Welsh Corgis, Boston Terriers, Boxers, Collies, Kelpies, Dachshunds, Miniature Poodles, Old English Sheepdogs, and Pekingese, though mixed breed dogs are also commonly seen.
Diagnosis rests mainly on history and physical examination. The key finding is a soft, fluctuant swelling beside the anus that can often be gently reduced with pressure. A rectal examination is central: your vet can feel the weakened pelvic floor, tell whether the rectal wall has deviated into the hernia, and check the prostate at the same time. Blood and urine tests give a baseline before surgery and can reveal kidney strain if the bladder has been trapped. X rays may show a rectum distended with stool or bowel loops in the wrong place, and ultrasound of the area helps confirm exactly which tissues, such as bladder, prostate, or intestine, have slipped into the hernia. Both sides are checked, even when only one swelling is visible.
Surgery to repair the weakened muscles is the most successful treatment and is indicated in essentially every case. The surgeon returns the herniated tissue to its proper place and rebuilds the pelvic floor, sometimes using nearby muscle flaps, and in severe or repeat cases a surgical mesh for support. Complex hernias may need an abdominal approach so organs can be secured in position. Neutering at the same time is strongly recommended: VCA Hospitals notes that dogs not neutered at surgery are almost three times more likely to develop another perineal hernia. Underlying causes of straining, such as prostate infection, are treated as part of the same plan.
While waiting for surgery, or when surgery truly cannot be done, stool softeners and a diet chosen by your vet keep stools easy to pass and reduce straining. Severe constipation may need manual removal of stool under sedation. Honest expectations matter here: the Merck Veterinary Manual reports recurrence in 10 to 46 percent of dogs after repair, along with a real list of possible complications, including infection, fistula formation, nerve injury, and rectal prolapse. That is why many vets refer these repairs to a surgical specialist, and why treating every source of straining is part of the operation, not an afterthought.
Home care centers on keeping stools soft and straining rare. Feed the diet your vet recommends, keep fresh water available at all times, and give any stool softener exactly as prescribed, reporting promptly if stools become hard again. After surgery, restrict activity as directed, protect the incision with a collar if your dog licks, and watch the area daily for swelling, discharge, or a return of the bulge on either side. Gentle short walks are usually fine once the surgeon agrees. Keep a simple note of how often your dog strains and whether urine flows freely, and bring that record to every recheck visit. Call sooner if anything changes. Small changes caught early are easier to fix.
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Usually not. Most perineal hernias develop slowly and can be assessed and planned for at a normal appointment. It becomes an emergency when the bladder slips into the hernia and blocks urine flow, or when a loop of intestine is trapped and loses blood supply. A dog that cannot urinate, vomits repeatedly, or becomes lethargic needs care the same day.
Hormones are strongly linked to the muscle weakening behind this hernia, and an enlarged prostate adds to straining. Neutering removes that hormone influence and shrinks the prostate over time, which lowers the load on the repair. VCA Hospitals notes that dogs left unneutered at surgery are almost three times more likely to develop another hernia, so the two procedures are usually planned together.
Yes, recurrence is a known risk even after a careful repair. The Merck Veterinary Manual reports that herniation recurs in 10 to 46 percent of dogs, which is why surgeons treat sources of straining, recommend neutering, and sometimes reinforce the repair. A new swelling on either side after recovery should be checked promptly, since a second repair is easier when the hernia is small.
No medicine can rebuild the torn pelvic floor muscles. Stool softeners, diet change, and treatment of prostate disease can reduce straining and buy time, and they matter when surgery must wait or cannot be done. But the gap itself remains, and the hernia usually grows. Surgery is the only treatment that closes the defect, which is why vets recommend planning it rather than waiting for a crisis.
That is the emergency form of this condition. A trapped bladder can twist so urine cannot leave the body, and toxins build up quickly while the bladder wall is starved of blood. The clinic will relieve the bladder, often with a catheter, give fluids, and stabilize your dog before surgery. Any dog with this hernia that strains without producing urine needs help immediately.
This page is general information drawn from the published guidance of the organizations listed under Sources below. It is not veterinary advice, and it does not replace your own veterinarian, who knows your dog. If your dog may have eaten something toxic, contact your veterinarian, the ASPCA Animal Poison Control Center on (888) 426-4435, or the Pet Poison Helpline on (855) 764-7661 straight away. A consultation fee may apply on the helplines. If your dog is struggling to breathe, has collapsed, is having a seizure that will not stop, or has a swollen belly with retching that brings nothing up, go to an emergency veterinarian now and do not wait to finish reading.
Last updated: November 2026. Facts on this page were checked against the sources listed above. How we work: our methodology.