Perineal herniation results when the components of the pelvic diaphragm no longer prevent pelvic and abdominal contents from passing into the subcutis adjacent to the anus. The levator ani is the muscle that most commonly atrophies, leaving a defect through which pelvic fat, prostate, bladder, rectum, or intestine herniates. The most commonly abnormally located structures are pelvic fat and rectum, which deviates into the perineum and leads to difficulty defecating. Paraprostatic cyst enlargement can occur caudally instead of intra-abdominally, leading to the appearance of perineal herniation. Perineal hernias occur most often in unaltered male dogs. Relaxin receptors were increased in the pelvic diaphragm musculature and prostate in affected dogs, and epidermal growth factor receptor expression was increased, its normal function is to decrease protein breakdown in skeletal muscle. EGF may also increase testosterone action, decrease collagen production, and increase matrix metalloproteinase activity.
Treatment includes castration and herniorrhaphy. Castration is possible through a caudal approach to the testicles. No difference was noted in postoperative recovery, healing, or complications. The caudal approach can be a bit challenging and may take longer to perform but it does avoid having to reposition the patient for the herniorrhaphy.
The standard surgery for perineal herniorrhaphy is internal obturator transposition with suturing of the coccygeus, levator ani (if present) and external anal sphincter. Post-operative issues that can arise include tenesmus (26%), dyschezia (20%), fecal impaction (9%), stranguria (12%), hematochezia (6%), urinary incontinence (6%), urinary tract infection (3%), and megacolon (3%). The fecal complications may be reduced with manual evacuation of the rectum at the time of surgery and the author treats all patients with stool softeners post-operatively for 1–2 months. Stool ideally will be soft and easily passed without straining. The dose should be adjusted to avoid diarrhea and firm feces.
Of great concern is the risk for reherniation (27%) or herniation on the contralateral side (9%). Recurrence can be late (1 y). Other complications include infection, dehiscence, rectal prolapse, fecal incontinence, sciatic nerve entrapment, and flatulence.
If the patient's tissues seem fragile, consider using reinforcement techniques. Some surgeons utilize polypropylene mesh for reinforcement of the hernia repair. The use of mesh has the risk of infection and related signs (5.6%) and recurrence was not avoided (12.5%). Natural material can also be sued to augment herniorrhaphy and should have decreased risk of rejection and perhaps infection. Alternatively, the patient's own tissues can be utilized, and fascia lata grafts have been reported. The most common complication is temporary lameness associated with the donor site.
If concerns exist for the ventral aspect of the repair, a semitendinosus flap can be used. The length of the muscle can be divided longitudinally, allowing the medial aspect to be transposed proximally. This technique was not always done alone, colopexy and ductus deferens pexy was done in some of the patients. The author prefers to use colopexy and deferens pexy in cases of recurrence.
Urinary bladder retroflexion can be complicated by urethral obstruction in patients with perineal hernia. If an owner opts against surgical repair, this complication and possible small intestinal entrapment should be discussed as possible fatal consequences. The urinary bladder can usually be catheterized, emptied, and reduced back into the abdomen prior to surgery. Cystocentesis following aseptic preparation over the bladder can be done and will usually allow urethral catheterization followed by reduction of the bladder into the abdomen. The patient should be stabilized prior to herniorrhaphy.
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