Hirschsprung Disease: Transanal Pull-Through

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CHAPTER 18 Hirschsprung Disease

Transanal Pull-Through

Stig Somme, Jacob C. Langer

Step 1: Surgical Anatomy

♦ Three important landmarks to consider for transanal pull-through:

The anorectal squamocolumnar junction (dentate line)—The mucosal incision should be made high enough that the transitional epithelium is preserved. If this epithelium is damaged, sensation will be abnormal and continence will be impaired.

The submucosal plane of the rectum—This method is relatively bloodless and permits the surgeon to prevent injury to the vagina or prostate during the initial dissection.

The plane along the outside of the rectal wall—Also relatively bloodless. The principal reason for staying in this plane is that it will prevent injury to pelvic structures. Blood vessels to the rectum must be divided just as they enter the rectal wall.

♦ The location of the pathological transition zone should be determined before beginning the anal dissection.

♦ In children with a more proximal transition zone, the normally innervated bowel might not reach the anus. In these cases a number of maneuvers can be performed, including dividing the lateral attachments of the descending colon, taking down the splenic flexure, and dividing mesenteric vessels proximally so that blood supply is maintained via the marginal vessels.

Step 2: Preoperative Considerations

♦ The diagnosis of Hirschsprung disease is suspected based on the clinical picture of intestinal obstruction, constipation, or enterocolitis. A contrast enema often shows a “transition zone.” However, around 10% of newborns with rectosigmoid Hirschsprung disease and all children with total colonic aganglionosis do not exhibit this finding.

♦ The diagnosis must be confirmed with a rectal biopsy reviewed by an experienced pathologist. The biopsy should be obtained from the posterior wall of the rectum about 1 cm proximal to the anorectal squamocolumnar junction (dentate line). The diagnosis is based on the absence of ganglion cells in an adequate specimen. A false-positive diagnosis may occur if the biopsy is taken too close to the dentate line or if there is not enough submucosa. There is controversy regarding the need for routine cholinesterase staining.

♦ Between the initial diagnosis of Hirschsprung disease and the definitive operation, rectal stimulations and irrigations should be performed as needed. If necessary, the infant can be discharged and scheduled for an elective operation at a later date. If this course is chosen, the parents must be taught how to perform rectal stimulations or irrigations before discharge and must be educated to recognize the signs of enterocolitis.

♦ In premature infants, it may be difficult for the pathologist to interpret a rectal biopsy because of the prematurity of the ganglion cells. These infants should be managed with rectal stimulation or irrigations or both until term, when a suction biopsy can be obtained.

♦ If long-segment Hirschsprung disease is suspected based on a radiologic transition zone extending proximal to the midtransverse colon or into the small bowel, we recommend performing a diverting stoma in the normally innervated colon or small bowel, followed by a Duhamel pull-through at a second stage after the stool has thickened.

♦ We do not perform formal bowel preparation for infants with Hirschsprung disease because they often become distended as a result of the distal functional obstruction. Instead, we recommend a washout in the operating room before beginning the operation.

Step 3: Operative Steps

Anesthesia

♦ General anesthesia with endotracheal intubation is used.

♦ A single-shot caudal block is achieved at the beginning of the operation and again at the end of the procedure. A caudal catheter should not be used because it is located too close to the surgical site.

♦ Prophylactic antibiotics, covering both coliforms and anaerobic organisms, should be given before the incision is made.

Position

♦ The infant is placed in lithotomy position, with the legs abducted at the hip joint and support under the knees to gain access to both the anus and to the abdomen.

♦ The infant is moved to the foot of the table so that the operating surgeon can sit on a stool below the child.

♦ During the perineal portion of the procedure, Trendelenburg positioning is helpful for visualization.

♦ A headlight is helpful to optimize visualization.

♦ A Foley catheter is optional. If a catheter is not used, the bladder can be intermittently emptied using a Coudé maneuver.

Irrigation

♦ Warm, diluted Betadine solution is used through a red rubber catheter to irrigate the colon until it is clean.

Leveling Biopsy

♦ We begin by making a supraumbilical incision, opening the fascia in a transverse fashion, including ligation and division of the umbilical vein.

♦ A Hegar dilator is carefully introduced through the anus and used to push the sigmoid colon toward the umbilical incision, where it is grasped with a Babcock clamp (Fig. 18-1). Care is taken to identify which part of the sigmoid is proximal and which is distal.

♦ A full-thickness biopsy is obtained from the antimesenteric border of the colon for immediate frozen-section evaluation. The biopsy site is closed using a running 4-0 PDS in a single layer, and the tail is left long for easy identification if additional biopsies are necessary. If a transition zone is identifiable by direct vision, the first biopsy is taken about 2 cm proximal to the transition zone. It must be recognized that the pathological transition zone is sometimes more proximal than either the grossly visible or radiologically evident transition zone.

♦ While waiting for the results of the frozen section, the mesentery to the colon distal to the biopsy can be divided either by ligation or by bipolar cauterization close to the bowel wall (Fig. 18-2).

♦ If the initial biopsies are aganglionic, additional biopsies must be obtained more proximally until normal ganglion cells are found.

♦ In cases with a more proximal transition zone, the umbilical incision can be used to divide the lateral attachments of the descending colon, take down the splenic flexure, or divide mesenteric vessels proximally so that blood supply is maintained via the marginal vessels.

Figure 18-1

Figure 18-2

♦ Four 4-0 silk sutures are placed to evert the anus (Fig. 18-3). Some surgeons prefer the Lonestar retractor, but we find that it tends to tear through the tissue in infants and is therefore more traumatic.

♦ With a nasal speculum in the anus, a circumferential mucosal incision is made using a needle-tip cautery (Fig. 18-4). The mucosal incision should be made 0.5 cm above the dentate line in an infant and up to 1.0 cm above the dentate line in an older child.

♦ Multiple 4-0 silk sutures are placed into the proximal edge of the mucosal incision for retraction. These sutures are brought together and secured with one straight hemostat.

♦ The dissection of the muscular cuff then proceeds using the needle-tip cautery (Fig. 18-5). The correct plane is in the submucosa, between the mucosa and the circular muscle fibers. It has a white appearance and is relatively avascular.

♦ The submucosal dissection is carried proximally for approximately 2 cm. At this point the muscular cuff is incised and divided circumferentially (Fig. 18-6), taking care to stay immediately on the outside of the rectal muscle.

♦ The dissection then proceeds proximally on the outside of the rectum, again taking care to stay immediately on the outside of the rectal muscle (Fig. 18-7). The rectal blood supply is divided as it enters the wall of the bowel. Most blood vessels can be “pinch-burned” (cauterized) and then transected. Larger vessels can be ligated and divided.

♦ Eventually the peritoneal reflection is encountered and divided so that the bowel that is pulled through is intraperitoneal. At this point, it is important to maintain the orientation of the rectum so that it is not twisted. A Kelly clamp can be placed in the vertical plane to maintain the orientation, which will prevent inadvertent 360-degree rotation of the bowel. Some surgeons also place sutures periodically along the antimesenteric surface of the rectum to ensure correct orientation.

♦ When the leveling biopsy site (proximal to the transition zone with confirmed ganglion cells) has been reached, the pull-through is extended for another 2 to 3 cm proximally to ensure that the transition zone is not included in the anastomosis (Fig. 18-8).

♦ The anterior half of the circumference of the normally innervated bowel is transected. The anastomosis is performed using interrupted 4-0 Vicryl sutures, starting with the 12, 3, and 9 o’clock positions. Bowel transection is then completed, the specimen passed off the field, and the 6 o’clock stitch is placed. The rest of the anastomosis is performed using a “divide and conquer” technique, bisecting the space between the initial stitches and then continuing to divide the spaces between sutures until the anastomosis is complete. It is important to obtain full-thickness bites of the pulled-through colon and generous bites of the underlying muscle on the distal rectum. It is also critical to ensure that the distal bites include only rectal mucosa and not transitional epithelium or skin (Fig. 18-9).

♦ When the anastomosis has been completed, a gentle digital examination is performed to ensure that it is patent and that there is no twist. In the very small infant, the anastomosis might not accept a finger, in which case an appropriate-sized Hager dilator should be passed.