Rectoperineal fistula is what traditionally was known as a low defect. The rectum is located within most of the sphincter mechanism. Only the lowest part of the rectum is anteriorly mislocated (Fig. 20.2). Sometimes the fistula does not open into the perineum, but rather follows a subepithelial midline tract, opening somewhere along the midline perineal raphe, scrotum, or even at the base of the penis. The diagnosis is established by perineal inspection. No further investigations are required. Most of the time, the anal fistula opening is abnormally narrow (stenosis). The terms "covered anus," "anal membrane," and "anteriorly mislocated anus," as well as "bucket-handle malformations" refer to different external manifestations of perineal fistulas. We prefer the term "rectoperineal fistula" as this is most descriptive. The opening is not an anus as it is not a normal anal canal and is not surrounded by sphincter. The term "fistula" therefore is more accurate.
The operation is performed in the prone position with the pelvis elevated. Multiple 6-0 silk stitches are placed in the fistula orifice. An incision, usually about 2 cm, is created dividing the entire sphincter mechanism located posterior to the fistula. The sphincter is
divided and the posterior rectal wall is identified by its characteristic whitish appearance. Dissection of the rectum begins laterally, which makes dissection of the anterior rectal wall easier to visualize.
Dissection of the anterior rectal wall is the most critical because even when these patients have a low malformation, the rectum is still intimately attached to the urethra. The most common, and feared complication in these operations involves injury to the urethra. The patient must have a Foley catheter in place. To avoid a urethral injury, the surgeon must be meticulous during the dissection of the anterior rectal wall, and must keep in mind that the common wall has no plane of dissection and two walls must be created out of one.
These patients have an excellent functional prognosis in terms of bowel control. However, they suffer from the highest incidence of constipation. When the problem of constipation is not treated properly, chronic fecal impaction and overflow pseudoincontinence can occur.
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