CHAPTER 18 Hirschsprung Disease
Transanal Pull-Through
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 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 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.
Step 3: Operative Steps
Anesthesia
♦ 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.
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.
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.
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