Congenital Pediatric Colorectal Disorders

Peter W. Dillon, MD
Professor of Surgery and Pediatrics
Penn State College of Medicine
The Milton S. Hershey Medical Center
Hershey, PA

Most congenital disorders of the colon and rectum in the pediatric population are discovered and treated in the neonatal or early infancy period making it rare for a primary congenital disorder in this region of the gastrointestinal tract to escape detection until adulthood. Though research efforts into a number of these problems have advanced our understanding of their etiology, pathophysiology, and embryonic mechanisms, the most important advances in the last decade have been in the surgical techniques used to correct these anomalies and the concomitant long-term outcomes for these young patients as they become adults. Common congenital colorectal disorders in children continue to be duplications, Hirschsprung's disease, and anorectal malformations.

Colonic and Rectal Duplications

Duplications of the gastrointestinal tract make up a very rare group of malformations that vary greatly in appearance, size, location, and symptoms. These anomalies have three defined characteristics: 1) the presence of a well-developed coat of smooth muscle; 2) the epithelial lining represents some portion of the alimentary tract; and 3) most duplications are intimately associated with a portion of the gastrointestinal tract. Duplications are either cystic or tubular in shape and have been reported to occur anywhere along the gastrointestinal tract from the tongue to the anus. They have been reported in 1 of every 4500 autopsies, and 15% are colonic and 5% rectal. Associated anomalies are relatively common and consist of vertebral, genitourinary, and genital malformations.

Clinical presentation depends on location and size of the duplication with 85% usually detected by 2 years of age. However, some duplications may remain silent and persist into adulthood. Colonic or rectal duplications may present as an abdominal mass with or without symptoms or as persistent problems of constipation, rectal prolapse, or chronic perirectal abscess. Neoplastic changes have been reported in both colonic and rectal duplications. Multiple diagnostic modalities may be necessary to identify these lesions including contrast studies, CT scan, technetium scan, ultrasonography, and colonoscopy.

Colonic duplications may be isolated cysts in the abdomen or pelvis or may have an external fistula to the perineum, an internal fistula to the urinary tract, or a communication with the normal colon. Type I duplications are above the peritoneal reflection and usually present as abdominal masses that may be accompanied with pain or bleeding. However, the incidence of ectopic gastric mucosa is much lower in colon duplications than in other anatomic sites. Type II duplications tend to be associated with other complex CNS or genitourinary malformations.

Though the preferred treatment for these congenital malformations is excision, this goal is not always possible, and the primary goal is to relieve the patient's symptoms. Smaller lesions can be excised as isolated lesions or by resecting the duplication and its attached normal colon. Long, tubular duplications usually have one or more openings into the normal colon, and enlarging these communications or making a distal communication by excising part of the common wall to allow reentry from the duplication into the normal colon may be the only surgical therapy necessary. It is not necessary to excise the mucosa of the duplication if contents have free egress into the normal colon.

Rectal duplications always occur in the retrorectal space, and almost half are associated with fistulas to the anal canal or perineal region. They can present with constipation, rectal bleeding, hematochezia, rectal prolapse, hemorrhoids, and abscess formation. When a retrorectal mass is found, radiographic evaluation with either a CT scan or MRI of the spine should be performed. Surgical techniques to remove the cyst include a transanal approach or a posterior sagittal or Kraske approach.

Congenital Aganglionic Megacolon - Hirschsprung's Disease

Hirschsprung's disease, or congenital aganglionic megacolon, is a relatively common cause of intestinal obstruction in the newborn occurring in approximately 1 of every 5000 to 7000 births. The male to female ratio in patients with classic Hirschsprung's disease is reported as 4:1 but approaches 1:1 with long segment disease. Most infants are diagnosed in the neonatal period, but up to 20% may be discovered at later time periods. Genetic studies indicate an increased familial risk for Hirschsprung's disease with inheritance rates in some kindreds approaching 50%. Abnormalities in the expression of the RET protooncogene have been reported.

This condition is characterized by an absence of ganglion cells in both the submucosal (Meissner's plexus) as well as the intermuscular (Auerbach's) plexus. Increased numbers of nerves as well as neural hypertrophy are also found in the aganglionic segment. Resulting imbalances in the adrenergic, cholinergic, and nitric oxide systems leads to decompensated smooth muscle contractility. The segment of aganglionosis is almost always continuous and passes through a transition zone of hypoganglionosis and persistent neural hypertrophy until the proximal ganglionic bowel is reached. Experimental investigations suggest that the aganglionosis results from a blockage of normal neural crest cell migration distally through the bowel wall layers. The level of colonic aganglionosis involves the rectosigmoid in approximately 80% of cases, the left colon in 7%, the transverse colon in 5%, and total colonic aganglionosis with variable small bowel involvement in 7 - 10% of patients.

Clinical Manifestations

Infants usually become symptomatic during the first 24 to 72 hours of life, and the classic presentation of Hirschsprung's in this time period is the delayed passage of meconium. Ninety-five percent of full-term infants will defecate in the first 24 hours of life, and the remainder will pass their first stool in 48 hours. Delayed passage of meconium beyond the first 72 hours of life is of concern and should raise the possibility of Hirschsprung's. Other signs and symptoms include abdominal distension, poor feeding, and bilious emesis. If not diagnosed until later years signs and symptoms include abdominal distension, chronic constipation, and failure to thrive.

The barium enema is still the primary diagnostic radiographic study and should be done in any suspected case before a rectal exam or washout enema is administered that might decompress the characteristic transition zone. Characteristic findings include a spastic distal segment extending proximally from the rectum through a transition zone into dilated proximal bowel. A follow-up film at 24 hours may show incomplete evacuation of the barium. The rectal biopsy is the diagnostic gold standard and can be done with a suction device in infants or with an open transanal approach in children and adults. Anorectal manometry can also be used to diagnose Hirschsprung's disease, but its use is limited in infants and children.

Management

In the past decade a significant evolution in the surgical treatment of Hirschsprung's disease has occurred. Previously, standard surgical therapy consisted of an initial leveling colostomy just above the transition zone at the time of diagnosis followed by definitive reconstruction around 6 months of age with ultimate closure of the protecting colostomy some time before a year of age. The acceptance of primary pull-through procedures in the neonatal period along with the development of minimally invasive surgical techniques has dramatically altered the timing and consequences of surgical intervention.

Definitive Operations

Swenson Procedure
Full thickness resection of the aganglionic portion of the colon is performed down to the level of the levator ani muscle and the dentate line. The dissection is kept precisely along the rectal wall to prevent collateral damage to surrounding pelvic structures. Ganglionated bowel is then mobilized and anastomosed to the anal canal by a conventional, transanal technique.

The Swenson procedure as a primary operation with laparoscopic assistance has been reported. However, a minority of American pediatric surgeons prefers this approach. Duhamel Procedure
The Duhamel procedure was devised to avoid the extensive pelvic dissection required in the Swenson operation. The original technique was subsequently modified by Martin to its present form. The distal aganglionic colon is mobilized to the peritoneal reflection where the rectal stump is divided and closed. The retrorectal space is mobilized in the posterior midline down to a level just above the dentate line. Through a transanal approach the posterior rectal wall is opened 1 centimeter above the dentate line. Ganglionated proximal bowel is then brought down the retrorectal space and anastomosed to the rectal opening. A linear stapling device is used to eliminate the common wall between the native rectal vault and the ganglionated colon to create a side-to-side anastomosis.

Long-term studies have shown that results with this surgical strategy have been quite good and tend to improve with time. Satisfactory bowel function has been reported in 80 - 100% of patients ten to twenty years following surgery, but reports of problems with constipation and fecal soiling in up to 25% of long-term patients have been noted. A potential technical problem with the Duhamel procedure is the growth over time of a colorectal septum or spur between the aganglionic and innervated portions of intestine after a stapled anastomosis. A blind pouch can occur with formation of a fecaloma. Resection of the enlarged pouch or stapled division of the spur may be required.

Soave Procedure
Franco Soave pioneered the development of the endorectal pullthrough for Hirschsprung's disease. Its unique feature is the minimization of risk to pelvic structures during the pelvic portion of the dissection. Boley then modified his procedure with the construction of a transanal single layer anastomosis 1 cm above the dentate line. The endorectal dissection is carried down to just above the dentate line leaving a rectosigmoid muscular cuff. Following eversion of the dissected mucosal sleeve out the anus and its amputation 1 cm above the dentate line, the normally innervated colon is brought through the muscular cuff and anastomosed to the anorectal mucosa. Originally conceived as an abdominal operation, uncomplicated rectosigmoid disease can now be approached transanally, while longer segments can be done transanally with laparoscopic assistance. This is probably the most common procedure done for Hirschsprung's at this time.

Factors that have been found to influence long-term outcomes include early surgical complications such as pelvic sepsis, the occurrence postoperatively of enterocolitis, and the requirement for further surgery. Current evidence suggests that the timing of successful definitive surgery is not critical in determining long-term results. As with the Duhamel, postoperative results improve with time. Persistent constipation can be one of the long term problems following a Soave, but its incidence appears to be less than with a Duhamel. Other reported problems have included diarrhea and rectal prolapse.

Total Colonic Aganglionosis
Though it represents only 5 - 10% of all cases of Hirschsprung's disease, patients with total colonic aganglionosis present a challenging problem. Morbidity and mortality rates tend to be higher for these patients, and many undergo multiple procedures and experience frequent perioperative complications. Extension of the aganglionosis into the small intestine can present even greater management difficulties. Current methods of reconstruction include a Soave type procedure with a straight ileoanal pullthrough, the Boley modification of that technique with the addition of a right colon patch to aid fluid reabsorption, and the Martin modification of a Duhamel procedure. Long-term complications with all of these procedures include failure to thrive, intractable diarrhea, and nighttime incontinence

Anorectal Malformations - Imperforate Anus

Malformations of the rectum and anus include a wide spectrum of defects ranging from the slight malposition of an anteriorly displaced or ectopic anus to complete agenesis of the anorectal canal. It is estimated that they occur in approximately 1 in 5000 live births though this may be an underestimation because of delayed diagnosis of many low or minor lesions. There appears to be a male preponderance (3:2), and most males have high lesions. Genetic abnormalities include Down's syndrome. Fifty to sixty percent of infants have associated malformations in other organ systems including cardiovascular defects (12%-22%), tracheoesophageal fistula (10%), duodenal atresia (2%), vertebral anomalies including spinal cord abnormalities (10%-46%), and genitourinary anomalies (5%-35%). Urologic abnormalities include vesicoureteric reflux, renal agenesis, cryptorchidism, and hypospadias. Vaginal and uterine anomalies include bicornate uterus, uterus didelphus, and vaginal septum.

Two different embryologic theories are currently invoked to explain these caudal malformations. In standard teaching it is proposed that defective formation of the urorectal septum accounts for the defects in both males and females. A recent theory suggests that defects in the dorsal cloaca and the absence of the dorsal cloacal membrane result in anorectal malformations early in gestational development. The lack of complete embryological understanding of these anomalies has not hindered attempts at developing surgical reconstructive procedures.

Several classification systems of these defects have been proposed in the surgical literature but have not been applied consistently. The most common method currently employed is to characterize these anomalies as either "high" or "low" based on their relationship to the levator muscle complex. With high lesions the rectum fails to descend through the levator muscles and may or may not have a fistulous connection to the urethra or bladder in the male or the upper portion of the vagina in the female. In a low lesion the rectum descends through the levator complex and may end with a fistulous cutaneous tract or a thin covering of skin.

Of note, the cloacal anomaly is the most complex female malformation involving a fusion of rectal, vaginal, and urinary developmental anomalies into a common channel.

Management

The management of infants with anorectal malformations has evolved considerably since the adoption of the abdominoperineal pullthrough in the late 1940's. For high lesions various staged approaches involving a diverting colostomy as the first procedure are giving way to primary repair in the newborn period. For low lesions meticulous reconstructive approaches are replacing simple cutback procedures. Laparoscopic techniques have also been reported. However, for complex malformations or medically compromised infants a diverting colostomy as the initial operation is still the safest approach. The goal of all of the techniques is the anatomical reconstruction of the anorectal region to maximize the potential for normal bowel function and continence.

Definitive Operations: High Lesions

Abdominoperineal Pullthrough
This procedure was proposed in the late 1940's and involves dissection of the rectourogenital fistula from an abdominal approach. The rectum is then pulled down anterior to the puborectalis muscle to a perineal incision. This technique is seldom used at this time. However, laparoscopic techniques have been reported that are very similar to this approach.

Anterior Perineal Approach
This technique was originally reported by Mollard. The fistula is identified and divided through an incision made anterior to the anal site after it is identified by electric stimulation. A transabdominal approach can be added to facilitate the mobilization and dissection. The perineal anastomosis is then made to a skin tube fashioned from the anterior incision through the external sphincter complex.

Posterior Sagittal Anorectoplasty (PSARP)
The posterior sagittal anorectoplasty originally proposed by Pena and deVries is now the most common technique employed in the repair of high lesions. An important feature of this technique is that the dissection and reconstruction of the anomaly can be performed under direct vision. Through a sagittal sacroperineal incision carried through the anal site, the various muscular layers of the sphincter complex are identified down to the levator region and divided in the midline. The distal rectal pouch is identified and opened. If a fistula is present, it is isolated with a submucosal dissection and closed. The rectal pouch is tapered and brought through the muscular anal canal to the skin with anatomic closure of the divided muscular layers.

The posterior sagittal approach is ideal for the repair of cloacal defects, as it provides access to the distal urinary tract, vagina, and rectum through one incision.

Definitive Operations: Low Lesions

Cutback Anoplasty
For an ectopic or anteriorly displaced anus this procedure is usually done in the newborn period. When combined with a Y-V advancement of anal mucosa to the skin, it provides satisfactory results. However, it is not appropriate for those lesions with significant anterior displacement where a limited posterior sagittal anorectoplasty or an anal transposition should be used.

Limited Posterior Sagittal Anorectoplasty
This procedure is suited for the ectopic anus with significant anterior displacement in both males and females as well as for rectovestibular fistulas in the female. It involves the same midline approach through the striated sphincter complex as in a regular PSARP without the deep parasagittal or levator dissection. The perineal body is reconstructed during closure, and usually no colostomy is required.

Anal Transposition
A circumferential incision is made around the displaced anus, and the rectum is then mobilized up to the level of the levator by sharp dissection close to the bowel wall. The site of the external sphincter is then identified with stimulation and a tunnel is created through it. The mobilized rectal segment is then brought through this tunnel and anastomosed to the skin.

Outcomes
Short-term complications following any of these procedures include voiding dysfunction, wound infections, anastomotic disruption with bowel retraction, and anal stenosis. Rectal mucosal prolapse may occur in as many as 25% of high repairs. Constipation after repair of both high and low lesions may be a troublesome long-term problem. Constipation and associated overflow incontinence with fecal soiling are the major functional complications following surgical correction of high lesions and have been reported in 10% to almost 75% of cases. Though usually managed with diet, medication, or an enema program, in severe cases it can lead to rectal or sigmoid dilatation requiring additional surgical intervention. In many patients this problem improves over time, as the patients pass through adolescence into adulthood.

The most important long-term outcome for these patients is bowel function and continence. Results are clouded by the fact that it is not clear how many patients who were born with imperforate anus actually have the capacity for normal bowel control if given proper anatomical correction. Continence rates with older surgical techniques have been disappointing. Long-term studies of the PSARP technique have yielded mixed results with continence rates reportedly varying from 0% to 41%. Although most patients are able to maintain some degree of social continence following a PSARP, various bowel management programs utilizing enemas, dietary restrictions, and special undergarments are often required. As they get older, many patients are starting to explore the possibility of secondary sphincter reconstructions.

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