CHILD CONSTIPATION ABDOMINAL RADIOGRAPH

Abdominal Radiograph and Transit Time
An abdominal radiograph is not indicated to establish the presence of a fecal impaction if the rectal exam reveals the presence of large amounts of stool. A retrospective study in encopretic children showed thatmoderate to large amounts of stool found on rectal examination had a high sensitivity and positive predictive value (greater than 80%) for predicting fecal retention determined by abdominal radiograph, even using the radiologists subjective interpretation.

However, the specificity and negative predictive value were 50% or less. When the systematic scoring system developed by Barr was used for the presence of fecal retention on radiograph, the sensitivity of moderate to large amounts of stool on rectal examination improved to 92%, and the positive predictive value was 94%.

However, the specificity was still only 71% and the negative predictive value was only 62%. This suggests that, when there is doubt about whether the patient is constipated, a plain abdominal radiograph is reliable in determining the presence of fecal retention in the child who is obese or refuses a rectal exam, or in whom there are other psychological factors (sexual abuse) that make the rectal examination too traumatic. It may also be helpful in the child with a good history for constipation who does not have large amounts of stool on rectal examination.

In a recent study the value of the Barr Score was compared to the colonic transit time. The Barr Score was shown to be poorly reproducible, with low inter-observer and intraobserver reliability, and there was no correlation with measurements of transit time. Some patients have a history of infrequent bowel movements, but have no objective findings of constipation. The history obtained from the parents and child may not be entirely accurate. In these patients an evaluation of colonic transit time with radio-opaque markers may be helpful.

The quantification of transit time shows whether constipation is present and provides an objective evaluation of bowel movement frequency. If the transit time is normal, the child does not have constipation. If the transit time is normal and there is no soiling, the child needs no further evaluation.

For children who have soiling without evidence of constipation the best results have been achieved with behavioral modification, but in some instances psychological evaluation and treatment may be necessary. If the transit study is abnormal or a fecal impaction is present, further evaluation will be needed. When a child with objective evidence of constipation is refractory to treatment, it is important to consider Hirschsprung disease.