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
In most cases, the most useful 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. Overflow diarrhea is suggested if the child has a history of diarrhea and there is large fecal burden on the radiograph. An abdominal radiograph can also be useful in assessing the colonic fecal burden among children who are obese or who refuse a rectal examination. It can also be helpful in assessing the efficacy of medical therapy when the child's history is unclear.
Due to the high frequency of unnecessary abdominal radiographs for pediatric patients with constipation in the ED despite evidence-based guidelines that recommend against imaging, [11, 12] a study by Ferguson et decreased the rates of abdominal radiographs from 62% to 24% by the use of an interventional improvement project that included grand rounds on constipation and sharing best practices. [13, 14]
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.
The image below illustrates megasigmoid and impacted stool, and thus, slow motility.
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 with 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. [15] 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.
Other Tests
A study by Doniger et al sought to determine the performance of point-of-care ultrasound using a sonographic numeric cutoff value for diagnosing constipation. The study found that in children with abdominal pain, there was a strong correlation of an enlarged transrectal diameter with constipation. [16]
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Plain abdominal radiograph that demonstrates stool throughout the colon.
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This table differentiates functional constipation from Hirschsprung disease.
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This unprepared single-contrast barium enema demonstrates a transition zone consistent with Hirschsprung disease.
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The images illustrate normal anorectal manometry with relaxation of the internal anal sphincter in response to rectal distention.
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This image delineates common withholding behaviors in young children.
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Contrast enema of a patient with megasigmoid and impacted stool.
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Contrast enema in a patient in whom the rectosigmoid was resected.
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Position for enema administration in an infant.
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Another position for enema administration.
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Administration of an enema.
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Incorrect enema administration. The enema is administered against stool impaction and cannot be successful.
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Enema administration with a tube.
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Enema with inflated Foley balloon catheter.
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Administration of an enema against impacted stool.
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Administration of an enema against fecal impaction.
