see also Anorectal Malformations
How is a posterior sagittal anorectoplasty (PSARP)  performed?
A Foley urinary catheter is placed after induction of anesthesia. A coudé catheter is helpful to avoid passage through a recto-urethral fistula. Cystoscopy may be required if the recto-urethral fistula is large or the urinary tract is difficult to cannulate.
The baby can be placed in either the prone or supine position. The prone, slightly jack-knifed position (with a roll under the hips) allows better visualization during the often challenging dissection of the anterior wall of the rectum from its fusion with the back wall of the vagina or urinary system. Whichever initial position is chosen, a total body preparation to include the entire lower part of the patient’s body is required in case the baby has to be flipped during the operation.
Placement of the rectum in the center of the anal muscle complex is essential for long term bowel control in those patients with a good potential for continence. Marking the likely position of the anoplasty with a pen or sutures prior to making an incision by confirming the location of the muscle complex with a muscle stimulator assists with orientation.
Traction sutures are place around any visible fistula. The subsequent incision is made circumferentially around the fistula and is continued posteriorly in the midline toward the coccyx. The length of the incision is variable depending upon the amount of exposure required.
In the absence of a fistula the posterior sagittal incision is made from just inferior to the coccyx and extended to the perineal body. It is essential to keep the dissection plane in the midline. Using the stimulator the parasagittal muscles can be seen running parallel to the incision and posterior to the muscle complex. The muscle complex fibers are identified as they run perpendicular to the incision. Uniform traction and frequent muscle stimulation ensures a midline dissection. Protrusion of unilateral ischiorectal fat indicates that the surgeon has strayed from the midline. In order to avoid posterior misplacement of the rectum it is important to visualize the perineal body fat anterior to the anal muscle complex and location where the muscle complex fibers cross the parasagittal fibers.
The position of the rectum can be predicted based on the preoperative distal colostogram. The dissection of the soft tissues is continued in the midline with separation of the levators until the white fascia of the rectum is encountered. Traction sutures are placed into the inferior aspect of the rectum and the rectum is opened in the midline to visualize the fistula.
The rectum is freed circumferentially by starting posteriorly (i.e. on the coccyx side) and laterally leaving the anterior aspect (the location of the fistula) for last. The fistula can identified with gentle probing with a lacrimal duct probe to confirm its location. The fistula is divided and the rectum dissected free.
Traction sutures are placed in the rectal mucosa just superior to the edge of the fistula to facilitate the dissection between the urethra and the rectum. Excessive bleeding during the anterior dissection indicates entry into the spongiosum tissue that surrounds the urethra.
In males, the urinary and reproductive systems can share a common wall with the anterior aspect of the rectum. In females the vagina is anterior and often has a common wall with the rectum. The lower the fistula the longer the common wall between the rectum and the anterior structures. This common wall must be divided to the level of the peritoneal cavity to assure sufficient rectal length to reach the perineum without tension. There is no true plane between these anterior tissues. It is created with even traction and careful dissection that must stay close to the rectal wall to avoid injury to the adjacent nerves while taking care to not enter the rectum.
Visualization of glistening white perirectal fascia is characteristic of a rectal dissection that is too wide. Dissection along the outside of the fascia will limit the ability to mobilize the rectum to the peritoneum, increase anastomotic tension and may cause a postoperative neurogenic bladder . To ensure proper mobilization and prevent injury it is important to remove this fascia and the extrinsic blood supply of the rectum. The distal rectum will remain well perfused based on its robust intramural blood supply. An adequate blood supply and a tension free anastomosis or one under minimal tension to help prevent prolapse will prevent complications such as stricture and dehiscence.
Once adequately mobilized the rectum is relocated posteriorly. The sphincters are again identified with the muscle stimulator to guide the next steps. The rectum is placed anterior to the levators which are reapproximated with multiple interrupted absorbable stitches. The perineal body is recreated with multiple layers of interrupted absorbable sutures and interrupted sutures in the skin.
The posterior aspect of the muscle complex is reapproximated behind the rectum incorporating the rectal wall with each of these stitches to help avoid prolapse. The soft tissue posteriorly is similarly closed with interrupted absorbable sutures.
The anal opening should be completely encircled by the sphincter complex and an anoplasty is then created. The colon is divided in half and sequentially anastomosed to the skin with sixteen full-thickness long lasting absorbable sutures placed through the bowel and skin. A size appropriate Hegar dilator should be passed into the anastomosis to ensure it passes freely.
What are the critical surgical considerations during repair of an anorectal malformation?
In males the key is to avoid injury to the urethra which is contiguous to the anterior rectal wall.
In females the dissection should adequately mobilize the anterior wall of the rectum to reach the areolar plane and thus fully separate the rectum from the vagina. This leaves no tension on the anoplasty which allows better perineal body healing.
When has the rectum been sufficiently mobilized?
The rectum should be free from the anteriorly located structures (urinary system in males and vagina in females) and therefore will be tension free when brought down to the perineum. The dissection should be continued superiorly until the areolar plane that exists where the two walls become separate.
What if the colon won’t reach the perineum in a patient with a previous colostomy?
If the initial diverting colostomy is created too distally the patient is at risk of this complication. The colostomy must be closed and this bowel used to gain length to the perineum. Given that there will now be two anastomoses recreating a diverting colostomy upstream is the safest strategy.
How is prolapse prevented and what is the role of tapering?
The posterior rectal wall should be tacked with several sutures from deep to superficial when re-approximating the posterior levator muscle complex. If the rectum is extremely dilated tapering may be necessary to avoid creating an anastomosis outside the muscle complex and stretching the supporting structures. It is often necessary to resect the last bit of rectum at the time of the anoplasty and to perform the anoplasty under slight tension so that the anal opening will pucker inward after healing .
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