Diagnosis should be suspected on rectal exam when the rectal vault is found devoid of stool and the anal canal feels narrow with increased tone. KUB often shows gaseous distention, in the neonate absence of gas in the pelvis is suggestive. Barium enema should be done unprepped with the tip just beyond the anal sphincter. Barium enema will reveal a transition zone with narrow segment and dilated proximal portion. Late films will show retention of barium at 24- 48 hours.
Rectal biopsy is the most reliable diagnostic measure.
Absence of ganglion cells in an infant is not conclusive because they may be small and monopolar. The presence of large nonmyelinated nerve fibers is helpful. Acetyl choline esterase histochemistry is helpful. The incidence of enterocolitis decreases after 3 months of age. Water intoxication results from the use of tap water enemas, or there may be hypertonic dehydration from saline and fleets enemas.