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What is Perineal hernia and explain in detail?
Perineal hernia is a hernia involving the perineum (pelvic floor).  The hernia may contain fluid, fat, any part of the intestine, the rectum, or the bladder.  It is known to occur in humans, dogs, and other mammals, and often appears as a sudden swelling to one side (sometimes both sides) of the anus.
A common cause of perineal hernia is surgery involving the perineum.  Perineal hernia can be caused also by excessive straining to defecate.  Other causes include prostate or urinary disease, constipation, anal sac disease (in dogs), and diarrhea.  Atrophy of the levator ani muscle and disease of the pudendal nerve may also contribute to a perineal hernia.

In humans
In humans, a major cause of perineal hernia is perineal surgery without adequate reconstruction.  In some cases, particularly surgeries to remove the coccyx and distal sacrum, adequate reconstruction is very difficult to achieve.  The posterior perineum is a preferred point of access for surgery in the pelvic cavity, particularly in the presacral space.  Surgeries here include repair of rectal prolapse and anterior meningocele, radical perineal prostatectomy, removal of tumors including sacrococcygeal teratoma, and coccygectomy.  Perineal hernia is a common complication of coccygectomy in adults, but not in infants and children (see coccygectomy).
The standard surgical technique for repair of perineal hernia uses a prosthetic mesh, but this technique has a high rate of failure due to insufficient anchoring.  Promising techniques to reduce the rate of failure include an orthopedic anchoring system, a gluteus maximus muscle flap, an acellular human dermis graft, and an acellular pig collagen graft.

In dogs and cats

In dogs, perineal hernia usually is found on the right side.  Most cases are in older intact (not neutered) male dogs (93 percent in one study)