**4. Hindgut disorders**

#### **4.1 Hirschprung's disease**

#### *4.1.1 Embryology*

Aganglionosis of the myenteric plexus due to failure of neural crest cell migration during weeks 6–12 of embryonic development. Most often occurs in the rectum though any portion and, rarely, the entire bowel can be affected. The myenteric plexus lies in between the outer longitudinal and inner circular muscle layers of the colon and is responsible for peristalsis.

#### *4.1.2 Clinical presentation*

Aganglionosis results in a functional obstruction manifesting as failure to pass meconium within first 24 h of life. Abdominal distention may be present. Rectal stimulation causes explosive passage of air and stool. Because disease is distal, infant will likely be able to tolerate oral intake though may have intermittent episodes of bilious emesis. Less severe disease may not manifest until later in childhood, up to 2–3 years of age, with chronic constipation. There is an association with trisomy 21. Therefore, work up includes echocardiogram to rule out concomitant cardiac defects.

#### *4.1.3 Diagnosis*

Gold standard is suction rectal biopsy, which demonstrates aganglionosis of the myenteric plexus. Biopsy should be obtained 1–1.5 cm proximal from the dentate line to ensure rectal specimen is obtained. Pathology will reveal unmyelinated nerve fibers with hypertrophied endings that stain darkly with acetylcholinesterase. Abdominal X-ray shows dilated proximal bowel with collapsed distal colon. Contrast enema is helpful in distinguishing transition zone between affected and normal colon however, gross anatomic distinction does not always correlate with histopathology [8].

#### *4.1.4 Surgical management*

Although various operative methods have been described, the fundamental principle of each procedure is the same: to establish continuity between the normal, ganglionic segments of bowel. In the past, multi-stage operations beginning with decompressive colostomy followed by definitive repair was common. Nowadays, single-stage laparoscopic approach is preferred. Regardless of procedure, however, intra-operative frozen section must be performed to confirm the presence of normal ganglionic colon prior to anastomosis, otherwise dysfunction will continue post-operatively.

#### *4.1.4.1 Swenson-original procedure*

The rectum/aganglionic segment is dissected circumferentially, everted through the anus and resected. Normal colon is pulled down and a low end-to-end colorectal anastomosis is created.

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greater degree.

*Congenital Anomalies of the Gastrointestinal Tract DOI: http://dx.doi.org/10.5772/intechopen.92588*

The aganglionic portion of bowel is bypassed and a posterior end to side anastomosis is created between the innervated segments of colon and distal rectum. The rectum is stapled at the proximal margin of disease. An incision is made in the distal posterior wall of the rectal stump approximately 1 cm superior to the dentate line. The innervated colon is pulled down through the presacral space and then anastomosed in an end-to-side fashion to the distal posterior rectal wall. The defunct

Circumferential endorectal dissection of rectal mucosa and submucosa, followed by evagination of these layers through the anus for resection. A rectal muscular channel remains, and innervated colon is intussuscepted through the remaining rectal muscular channel. A colorectal anastomosis is performed at the distal end of

No single procedure has been shown to be superior to other in terms of longterm outcomes, and up to 90% patients will have relatively normal bowel function following repair. Although results tend to be quite favorable, one significant cause of significant morbidity and mortality is Hirschsprung's enterocolitis. While the exact etiology of this entity is unknown, bacterial overgrowth and translocation appear to be implicated. Patients present with fever, abdominal distention and diarrhea. Management consists of fluid resuscitation, IV antibiotics and rectal irrigation. Refractory cases require surgical decompression with a proximal ostomy. Other complications such as anastomotic leak, stricture, abscess, wound infection

During the 5th week of gestation, the midline urorectal septum descends in a caudal direction toward the cloaca and divides into ventral and dorsal portions. The ventral bud becomes the urogenital sinus, which develops into the urethra and bladder. The dorsal bud becomes the rectum and anal membrane. The anal membrane involutes around week 8, thereby forming the anus. Dysgenesis can occur at any

An anatomical distinction based on the pathology's relation to the levator ani muscle complex was first described by Pena. The levator ani complex supports the pelvic floor and is composed of three striated muscles: the puborectalis, the pubococcygeus and the iliococcygeus. The puborectalis encircles the base of the rectum, helps to form the external anal sphincter and thereby plays an integral role in regulating defecation. Anorectal dysgenesis above the levator ani muscles is considered a "high" lesion. Conversely, lesions inferior to the levator ani complex are termed "low" malformations. Generally speaking, higher malformations tend to cause more severe issues with controlling defecation as the neuromuscular development between the levator ani complex and growing recto-anus is compromised to a

*4.1.4.2 Duhamel procedure*

rectal stump is left in place.

*4.1.4.3 Soave procedure*

the muscular channel [9].

and obstruction occur in up to 10% cases [1].

**4.2 Anorectal malformation/imperforate anus**

time point, allowing for variability in clinical presentation.

*4.1.5 Outcomes*

*4.2.1 Embryology*
