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.  To achieve this requires a balance of sensation, sphincteric control, and motility. 
The term 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.
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.
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 occurring in patients who do not have a clearly defined histologic defect in a portion of their colon. For example, children who are born with no evidence of Hirschsprung disease but still have severe constipation are considered 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.  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.  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 its treatment remain controversial.
Some patients have hypoganglionosis on biopsy. No definite criteria for hypoganglionosis have been 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.
Everything about pediatric colonic motility disorders remains controversial. The medical community that treats colorectal problems in adults espouses many concepts and methods that have been incompletely validated, such as artificial sphincters, cinedefecography, anorectal manometry, and biofeedback. The community that treats pediatric patients remains divided about intestinal neuronal dysplasia, ultrashort Hirschsprung disease, and achalasia of the sphincter.
It is to be hoped that future work will further define the spectrum of motility disorders of the bowel in children. This knowledge may lead to better-targeted therapies or more focused surgical approaches.
Innervation of the normal colon is derived from the autonomic nervous system and involves the following three distinct plexuses:
Auerbach plexus, located between the inner circular and outer longitudinal smooth muscle layers
Henle plexus, located at the inner margin of the circular muscularis propria
Meissner plexus, located 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 varies considerably; 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 a generally accepted indicator. When a patient is being evaluated for Hirschsprung disease, a biopsy sample must be obtained above this normal aganglionic zone.
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.
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; however, this theory 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, it is not clear precisely how these findings relate to the symptomatic intestinal dysmotility. 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
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.
If colonic motility problems are aggressively treated, the outcome for most children is excellent. The overwhelming majority can become clean with a laxative regimen. Children whose conditions are unmanageable with laxatives may do well on enema regimens or may benefit from surgical treatment if they have isolated megasigmoid or megarectum. Children rarely have conditions so refractory to medical management that they require a diverting ostomy. Such cases are usually referred to as intestinal pseudo-obstruction, which is essentially a diagnosis of exclusion.
Most parents wish to know if their child will require laxatives or enemas for life. This question is difficult to answer; however, unless something changes in the colon, the answer is “perhaps.”
Some patients do require laxatives or enemas for life. Others can often avoid the need for traditional medication laxatives by increasing their ingestion of laxative foods and soluble fiber. Children tend to be finicky eaters and typically do not do well with such dietary restrictions. When they are old enough to understand the importance of laxative foods and fiber, they can often cut down or even eliminate their use of additional laxatives. This occurs only with older children or young adults who become self-motivated.
Parental desire alone is rarely effective in making a willful child become compliant. The final answer to the question posed above will not be clear until the child has become an adult and is ready to assume responsibility for his or her own care and quality of life.
What would you like to print?