Constipation is a common problem that affects 30% of children; it is usually associated with maladaptive behavior triggered by a painful or otherwise unpleasant defecation. In the United States, the average healthcare cost for the management of children with constipation is estimated to be $3430/year compared to $1099/year for children without constipation. Functional constipation is responsible for more than 95% of cases of constipation in healthy children 1 year of age and older.
PATHOGENESIS AND EPIDEMIOLOGY
The frequency and type of stools vary with a child’s age and diet. Ninety percent of newborns pass meconium within 24 hours of birth. In the neonatal period, infants pass an average of 4 stools per day. During the first 3 months of life, infants pass an average of 2 stools per day if formula fed and 3 stools per day if breastfed. The stooling frequency reduces to 1 to 2 stools per day by age 2 and 1.2 stools per day by age 4. The mean gastrointestinal transit time is 8.5 hours at 1 to 3 months of age, 16 hours at 4 to 24 months of age, 26 hours at 3 to 13 years of age, and 30 to 48 hours after puberty.
Normal defecation requires propulsion of the stool into the rectum, which serves as a storage area (Fig. 381-1). The sensation to defecate when the rectum is full is associated with rectal smooth muscle contraction and reflex partial inhibition of the internal anal sphincter (Fig. 381-2), which allows the stool to impinge on the sensory area of the upper anal canal. To achieve continence, the child must be able to perceive this urge to defecate, and if the social consequences of passing the stool at that time are appropriate, the child must plan to find a bathroom, depending upon the urgency. This is not an innate ability but requires learning in a supportive environment. The urgency of defecation will depend on the degree of this inhibition and stool descent that can be temporarily relieved by external anal sphincter and pelvic floor contraction. Once the child decides to defecate, the puborectalis muscle is relaxed, allowing the pelvic floor to descend and straighten the anorectal angle from the usual 85° to 105°. The expulsion of stool then requires an increase in intra-abdominal pressure by bearing down. If defecation needs to be postponed, the external anal sphincter can be voluntarily closed and the gluteal muscles can reinforce the pelvic outlet pressure, pushing the stool back into the rectum. Children with functional fecal retention commonly adopt postures and positions to augment the gluteal muscle action to prevent the stool from coming out.
Fecal incontinence results from the rectal fecal mass stretching open the anal sphincter; the liquid stool seeps around it and leaks out of the anal canal.