The patient is placed in the prone position with the pelvis elevated. The use of an electrical stimulator to elicit muscle contraction during the operation is very helpful. This contraction serves as a guide to keep the incision precisely in the midline, leaving equal amounts of muscle on either side. The length of the incision varies with the type of defect and can be extended to achieve the necessary exposure to effect a satisfactory repair. Thus, a perineal fistula requires a minimal posterior sagittal incision (2 cm), whereas higher defects may require a full posterior sagittal incision that runs from the middle portion of the sacrum towards the base of the scrotum in the male. The incision includes the skin, subcutaneous tissue, para-sagittal fibers, muscle complex, and levator muscles (Fig. 20.1). In simple defects (perineal), the incision includes the parasagittal fibers and the muscle com-
Table 20.1 Classification of anomalies (according to Peña , with permission)
Cutaneous (perineal fistula) Rectourethral fistula Bulbar Prostatic Rectobladderneck fistula Imperforate anus without fistula Rectal atresia
Cutaneous (perineal fistula) Vestibular fistula Imperforate anus without fistula Rectal atresia Cloaca
plex, and it is not usually necessary to expose the levator ani muscle. Once the sphincter mechanism has been divided, the next most important step of the operation is the separation of the rectum from the urogenital structures, which represents the most delicate part of the procedure. Any kind of blind maneuver exposes the patient to a serious injury during this part of the operation .
About 90% of defects in boys can be repaired via the posterior sagittal approach alone without an abdominal component . Each case has individual anatomical characteristics that mandate technical modifications. An example is the size discrepancy frequently seen between an ectatic rectum and the space available for pull-through. If the discrepancy is significant, the surgeon must tailor the rectum to fit. The number of rectums that need tapering is decreasing, probably because patients are receiving better colos-tomies, and the babies are undergoing the main repair earlier in life so that the distalrectosignoid does not have time to dilate.
A posterior sagittal approach should never be attempted without a technically adequate high-pressure distal colostogram to determine the exact position of the rectum and the fistula . Attempting the repair without this important information significantly increases the risk of nerve damage, damage to the seminal vesicles, prostate, urethra, ureters, bladder neck, and bladder denervation .
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