Pediatric Colonic Motility 

Normal bowel function is the end result of a complex interaction of systems, many of which are still poorly understood. Fecal continence may be defined as the ability to remain clean, with no leakage of stool, between voluntary bowel movements.^[1] To achieve this requires a balance of sensation, sphincteric control, and motility.^[2]

Motility refers to the peristaltic motion of the intestine. The colon receives liquid stool from the small intestine and slowly transports it to the rectum. During this journey, which usually takes 24 hours, water is absorbed from the liquid stool, and a semisolid product is presented to the rectum.

Colonic motions include various nonpropulsive contractions, as well as propulsive and mass peristalsis. Propulsive peristalsis consists of slow, irregular contractions that proceed in a craniocaudal direction. Mass peristalsis occurs several times daily and consists of a large peristaltic wave that moves contents toward the rectosigmoid. This peristalsis is suspected to be predominantly related to the gastrocolic reflex (ie, colonic contraction) stimulated by food passing out of the stomach into the small intestine.

Rectal motility differs from colonic motility in that it remains stationary and allows the stool to remain there until a socially acceptable time, when a massive contraction (mass peristalsis) pushes the stool out and completely empties the rectum.

Most patients with colorectal motility disorders have a system that moves too slowly and fails to completely empty. In the pediatric population, rapid colonic transit is usually unrelated to an inherent dysmotility. Instead, it is often related to short colonic length (either congenital or after surgery) or an intra-abdominal inflammatory process, such as appendicitis with rupture or inflammatory bowel disease. If the colon moves too slowly, stool accumulates and becomes hard and difficult to eliminate. This situation leads to fecal impaction. Eventually, liquid stool above the impaction leaks around the stool ball, and the patient seems incontinent. This is actually a pseudoincontinence referred to as encopresis (see Encopresis).

Many conditions affect colonic motility. Some babies are born with Hirschsprung disease, which is characterized by the absence of relaxatory ganglion cells in the distalmost colon. This problem is correctible with surgery, but children can still have constipation after the surgery. Other children are born with no evidence of Hirschsprung disease but still have severe constipation. These patients are said to have idiopathic constipation.

Several subsets of idiopathic constipation are described. Patients with an essentially normal biopsy result who lack an anorectal inhibitory reflex on manometry may be said to have ultrashort Hirschsprung disease.^[3] This disease entity and its treatment remain controversial. Differentiating this disease from another equally controversial entity, referred to as achalasia of the anal sphincter, is difficult.

Intestinal neuronal dysplasia (IND) is another controversial disorder.^[4] Meier-Ruge originally described this condition in 1971, and it most likely represents a spectrum of neural-crest malformations rather than a distinct disorder. Both its diagnosis and treatment remain controversial.

Some patients have hypoganglionosis on biopsy. No definite criteria for hypoganglionosis are established, and the finding may simply represent the result of chronic colonic dilatation secondary to stool retention. The ganglion cells may appear to be fewer than normal because they are spaced far apart.

Frederick Ruysch described megacolon in children as early as 1691. Danish pediatrician Harald Hirschsprung published the classic description of congenital megacolon in 1886. Tittel noted aganglionosis in 1901, but it was not identified as the etiology of Hirschsprung disease until Swenson and Bill published their article in 1948. After Hirschsprung disease was clarified, children with severe constipation but no quantifiable histologic defect were characterized as having idiopathic constipation. Meier-Ruge first described IND in 1971.

Constipation is defined as difficult, incomplete, or infrequent evacuation of stool. The stool may be hard, but this feature is not essential.

Idiopathic constipation is defined as constipation in patients who do not have a clearly defined histologic defect in a portion of their colon.

Frequency

Idiopathic constipation is the most common intestinal dysmotility disorder in children, but its true incidence is unknown. Although constipation affects more women than men, it affects more boys than girls.

Hirschsprung disease occurs in roughly 1 in 5000 children, with a male preponderance for the most common (short segment) form of the disease.

The etiology of idiopathic colonic dysmotility remains unclear. Inadequate water intake is not the cause of constipation for otherwise healthy children.

Many physicians believe that children most commonly retain stool for psychological reasons. Although some children who have severe constipation eventually develop a psychological component to their disorder, this is usually secondary. Primary stool retention is rare and often follows a discernible traumatic event, such as a painfully hard stool with a resulting fissure.

Some have implicated incomplete relaxation of the anal sphincter as the primary causative factor, although this does not adequately explain these conditions.

Although a definite etiology is unknown, various abnormalities have been identified in children who have slow-transit constipation. However, the way in which these findings relate to the symptomatic intestinal dysmotility is unclear. Abnormalities observed in children with slow-transit constipation include the following:

• Decreased quantity of substance P in intestinal nerve fibers
• Decreased number of interstitial cells of Cajal
• Decreased number of ganglion cells (hypoganglionosis)
• Abnormalities in colonic monoclonal antineurofilament antibodies
• Decreased plasma levels of motilin
• Increased plasma levels of pancreatic polypeptide

Children with idiopathic constipation have intestinal hypomotility. Their colons move more slowly than normal, and their rectums may incompletely evacuate without assistance. This leads to stool remaining in the colon for several days, during which time it dries out, resulting in large, hard stools. The colon eventually becomes dilated to accommodate this enlarged quantity of stool. As the bowel dilates, its hypomotility worsens, exacerbating the original problem. Fecal impaction eventually occurs.

Trying to pass large hard stools can be painful. It can even cause an anal tear or fissure, which is exquisitely painful and may instill in the child the desire to avoid having a bowel movement. This is the beginning of stool-holding behavior, which can be difficult to break.

History

A complete birth history must be obtained, including the first passage of meconium. Failure to pass meconium in the first 24-36 hours is associated with Hirschsprung disease. Any history of constipation from birth and multiple bouts of enteritis with diarrhea and distension suggests undiagnosed Hirschsprung disease. All children with such findings need both contrast enema and biopsy. History of meconium plug, constipation, and recurrent pulmonary issues, suggests cystic fibrosis and requires a sweat test. All children who present with rectal prolapse require sweat testing.

Children with idiopathic constipation often present with abdominal pain and distension. Their condition may be mistaken for appendicitis when the pain is in the right lower quadrant but can usually be distinguished because of chronic issues such as delayed passage of stool and, perhaps, soiling. Such children have probably been examined by several physicians for the problem and may have been referred to a psychologist for stool-holding behavior.

Many children present with fecal impaction with or without soiling. Fecal incontinence is a common presenting complaint.

Pertinent questions in the history include ”How often does the child stool?” and ”What is the character of the stool?” Determining if the child is still wearing diapers because of accidents is important; if the child is not still wearing diapers, determining how often the child stains the underwear or has accidents is important. By the time children present to a surgeon's office, they have usually tried most commercially available laxatives and enemas, and their parents are frustrated.

Physical examination

Comprehensive physical examination must be done to exclude a systemic illness manifesting with ileus or other nonidiopathic causes of constipation. In otherwise healthy children with normal physical findings, the abdominal examination is the most pertinent study. The abdomen may be distended or tympanitic but is rarely tender. If the child is put at ease and if he or she can be examined well, firm stool may be palpable in the left side of the abdomen. Rectal examination should be reserved for the end of the consultation because it often renders the child uncooperative. The rectal examination usually reveals the child's present state of cleanliness, which allows the examiner to put the presenting complaints into perspective. Look for any anatomic abnormalities, such as trauma, skin tags, fissures, fistulas, perirectal abscesses, polyps, or rashes.

Small babies may not be able to undergo digital rectal examination, and their anus should be sized with a Hegar dilator to rule out congenital stenosis. In full-term babies, the average anal diameter is 12 mm.

Surgery is only indicated for the treatment of non-Hirschsprung colonic motility disorders for which conventional therapies fail. Most patients who present to a surgeon with a motility disorder are already thought to have a condition refractory to laxative or enema administration. See the image below.

The clinician should personally direct an aggressive course of nonoperative treatment before considering a surgical option. (See Treatment.)

If Hirschsprung disease cannot be completely excluded based on the patient's history and imaging studies, suction or full-thickness rectal biopsy must be performed (see Hirschsprung Disease).

For all other children whose condition proves refractory to laxatives, contrast enema is then performed to determine if any segments of the colon are dilated. Children with a normal-caliber colon or total colonic dilatation usually do not do well with surgical resection. If their condition proves refractory to laxatives, it should be treated with daily enemas. If they do well with a rectal enema regimen, a continent appendicostomy (Malone procedure) may be fashioned as a conduit to ease enema administration and to increase the child's independence. Some clinicians use percutaneously placed cecostomy buttons for the same purpose.

Children with conditions refractory to laxatives and isolated rectosigmoid dilatation on contrast enema may benefit from sigmoid resection and primary anastomosis.

Surgical indications for intestinal neuronal dysplasia (IND) remain unclear. Currently, further study is required to clarify the role, if any, of surgery. Surgical indications for ultrashort Hirschsprung disease or sphincter achalasia are also controversial. Some surgeons advocate myectomy or injections of botulinum toxin, although results widely vary.

Innervation of the normal colon is derived from the autonomic nervous system and involves 3 distinct plexuses. The Auerbach plexus is between the inner circular and outer longitudinal smooth muscle layers. The Henle plexus is located at the inner margin of the circular muscularis propria. The Meissner plexus is beneath the muscularis propria. These plexuses are present throughout the colon and terminate above the level of the dentate line. The level at which they terminate widely varies; however, the presence of a normal aganglionic zone above the dentate line that extends cranially for a short distance and varies with age and size is generally accepted. When evaluating the patient for Hirschsprung disease, a biopsy sample must be obtained above this normal aganglionic zone.

Children who have Hirschsprung disease should undergo surgical treatment for that condition. The aganglionic colonic segment is excised, and the ganglionated bowel is brought down to the anus. Several procedures are described for this condition, with no single procedure demonstrating clear advantages or disadvantages in terms of outcome.

For children with idiopathic constipation, sigmoid colectomy is contraindicated if no segmental dilatation is demonstrable on contrast enema study.

Button cecostomy or Malone appendicostomy is contraindicated if a child's condition is not yet well managed with an enema regimen. These procedures change the route of enema administration but do not improve the efficacy of an enema. If the enema regimen has not been fine-tuned from the rectal route, adding a Malone or a cecostomy button does not improve the condition.