Pediatric Constipation Workup
- Author: Stephen Borowitz, MD; Chief Editor: Carmen Cuffari, MD more...
Approach Considerations
Constipation is recognized and diagnosed by most practitioners based on the child's clinical presentation (eg, a patient has difficulty passing stool or has not passed stool in 1-3 days). Laboratory studies are generally unnecessary unless an underlying condition is suspected to be the cause, in which case diagnostic tests should be obtained as appropriate.
Abdominal Radiography
The most important radiologic study for the evaluation of patients with bowel problems is plain abdominal radiography (see the following image). This helps the clinician determine how much stool is present in the colon and helps confirm or refute the history of either constipation or diarrhea. This modality is also useful in assessing the colonic fecal burden among children who are obese or who refuse a rectal examination. An abdominal radiograph can also be helpful in assessing the efficacy of medical therapy when the child's history is unclear.
Plain abdominal radiograph that demonstrates stool throughout the colon. Contrast Enema
Radiography can be useful in excluding or diagnosing Hirschsprung disease. Although the diagnosis of Hirschsprung disease ultimately relies on histologic demonstration of an absence of ganglion cells in the affected colon, the diagnosis is often suggested by single-contrast barium enema. The radiologist is looking for a change in colonic diameter from the narrow aganglionic segment to a more dilated ganglionic segment. This transition zone is characteristic of Hirschsprung disease and is shown in the image below.
This unprepared single-contrast barium enema demonstrates a transition zone consistent with Hirschsprung disease. A contrast can be performed to help evaluate the patient's colonic motility. Findings from this study help determine whether patients have slow motility or fast motility.
The image below illustrates megasigmoid and impacted stool, and thus, slow motility.
Contrast enema of a patient with megasigmoid and impacted stool. Avoid air-contrast enemas and rectal manipulation
Do not use an air-contrast enema when looking for Hirschsprung disease, because radiographic evaluation of Hirschsprung disease depends on finding a change in colonic caliber between the normal and abnormal aganglionic segment. With an air-contrast study, the colon is evacuated prior to the study to identify mucosal abnormalities. By evacuating the colon before the study, any caliber change may be masked.
Moreover, do not perform any form of rectal manipulation on the child (eg, rectal examination, therapeutic enema, suppository) for 48 hours before the procedure. Rectal manipulation with suppositories or therapeutic enemas may transiently dilate the narrowed distal segment, causing a false negative result.
Although an unprepared barium enema has reasonably good diagnostic sensitivity and specificity in older children, this procedure is substantially less reliable during the first several months of life. The proximal colon may require several months after birth to dilate sufficiently for a transition zone to be apparent.
Anorectal Manometry
Anorectal manometry can be useful in discriminating between functional constipation and Hirschsprung disease. A balloon catheter is inserted into the rectum during this test. Normally, when the rectal balloon is inflated, the internal anal sphincter relaxes reflexively (anorectal reflex), as is shown in the image below.
The images illustrate normal anorectal manometry with relaxation of the internal anal sphincter in response to rectal distention. Among patients with Hirschsprung disease, the internal anal sphincter fails to relax in response to rectal distention. As many as 20% of healthy children may have a falsely absent reflex, especially if they were born prematurely or at low birth weight; however, a positive response is strong evidence against Hirschsprung disease.
Rectal Biopsy
Rectal biopsy is the definitive means of establishing or excluding Hirschsprung disease.[11] This procedure is usually unnecessary when the clinical picture and the radiologic findings are characteristic of idiopathic constipation.
The tissue is examined histologically for the presence or absence of ganglion cells in the submucosal plexus. If the patient's rectum has no ganglion cells, the diagnosis of Hirschsprung disease is confirmed.
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