Severe Pediatric Constipation Workup

Updated: Aug 14, 2019
  • Author: Marc A Levitt, MD; Chief Editor: Harsh Grewal, MD, FACS, FAAP  more...
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The most important radiologic study for the evaluation of patients with bowel problems is a plain abdominal radiograph. 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.

A contrast enema should be performed to evaluate the patient’s colonic anatomy. Findings from this study help the clinician infer whether patients are likely to have slow motility or fast motility.

In a patient with functional constipation, the colon (particularly the rectosigmoid) may be dilated, redundant, or both. If, in a patient with an anorectal malformation (ARM), the contrast study reveals a straight colon on the left side, then the rectosigmoid was resected during imperforate anus repair; such a patient has fast motility (see the first image below). If the contrast study reveals a megarectosigmoid, the rectum was preserved during the original operation, and the patient has slow motility (see the second image below).

Contrast enema in a patient in whom the rectosigmo Contrast enema in a patient in whom the rectosigmoid was resected.
Contrast enema of a patient with megasigmoid and i Contrast enema of a patient with megasigmoid and impacted stool.

A contrast enema should be performed with hydrosoluble material (never barium). It is the most valuable study for confirming the diagnosis of functional constipation and assessing for Hirschsprung disease.

The dilatation of the colon extends all the way down to the level of the levator mechanism, which is recognized because it coincides with the pubococcygeal line. The lack of dilatation of the rectum below the levator mechanism (pubococcygeal line) should not be interpreted as a transition zone or nondilated aganglionic bowel, because under normal circumstances, the anal canal and the part of the rectum below the levator mechanism are collapsed by the effect of the striated muscle tone from the sphincter mechanism. The rectum above the anal canal is extremely dilated, as is the sigmoid.

The contrast enema in patients with functional constipation reveals different degrees of dilatation and redundancy of the rectosigmoid, as is expected in a spectrum-type condition. Most interestingly, a dramatic size discrepancy is noted between a normal transverse and descending colon and an extremely dilated megarectosigmoid.

These changes are actually the reverse of what is observed in patients with Hirschsprung disease. The colon in a patient with Hirschsprung disease is dilated only proximal to the aganglionic segment, which remains nondilated.


Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is an excellent tool for determining whether a patient who has previously undergone imperforate anus repair has a correctly located rectum. A specific MRI protocol that involves placement of a rubber tube in the rectum reveals whether the rectal pull-through trajectory was placed within the sphincter mechanism.

MRI of the spine is sometimes needed to evaluate for an associated spinal condition as the cause of the constipation.


Anorectal and Colonic Manometry

Anorectal manometry is used by many practitioners. [6]  According to the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) and the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN), the main indication for performing anorectal manometry in the evaluation of intractable constipation is to evaluate for the presence of the rectoanal-inhibitory reflex. [7]

Traditionally, anorectal manometry is performed by placing a balloon in the rectum while measuring the pressure of the anal canal. Under normal circumstances, when the rectal balloon is inflated, the pressure within the anal canal decreases; this is described as the rectoanal inhibition reflex (RAIR). Pressure that does not decrease in the anal canal is considered abnormal and is said to be a sign of lack of relaxation of the internal sphincter. This is also considered diagnostic for Hirschsprung disease; however, it must be confirmed by rectal biopsy.

Manometry can also diagnose anal sphincter achalasia, in which the RAIR is absent but Hirschsprung disease is excluded with a normal biopsy. This condition that causes constipation and can be treated with injection of botulinum toxin in the anal canal. Anorectal manometry can also diagnose pelvic floor dyssynergia (by illustrating an abnormal push test), which could be treated with biofeedback.

Colonic manometry, which measures propagation of peristalsis through the colon, is valuable in determining which specific part of the colon is working and which is not and can help guide decisions such as which laxatives may work, whether an antegrade option (cecostomy or Malone) might be useful, and whether a colonic resection is required. In some patients, it may also diagnose diffuse dysmotility of the colon, which considerably impacts decision making and could prompt the need for a temporary ileostomy.


Biopsy and Histologic Findings

Rectal biopsies are usually performed with the specific purpose of ruling out Hirschsprung disease. The study is usually unnecessary when the clinical picture and the radiologic findings are characteristic of functional constipation.

Rectal biopsies are performed if the contrast enema reveals findings that suggest aganglionosis or if the patient behaves in a way that is clinically similar to a patient with Hirschsprung disease. If the patient has episodes of enterocolitis and does not soil, Hirschsprung disease is suspected. If the rectal examination reveals an empty rectum and the patient is still impacted above the reach of the finger, consider Hirschsprung disease and perform a biopsy. Pathologic findings consistent with Hirschsprung disease include the absence of ganglion cells and the presence of hypertrophic nerves.

A study by Tran et al found that younger patient age and shorter duration of constipation at the time of rectal biopsy were predictors of successful outcomes (defined as three or more bowel movements weekly for 4 weeks or longer, with no more than two fecal incontinence episodes monthly, irrespective of laxative use). [8]