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the study may result in decompression of the proximal bowel, with loss of
definition of the transition zone. When a clear-cut transition zone is seen, it is not
necessary to fill the colon with barium more than 12 to 18 in. above the transition
point. However, it is important not to empty the colon of barium at the end of the
study. The presence of retained barium above the transition point 24 hours later
strongly suggests the diagnosis of Hirschsprung disease.

FIGURE 116.16 Hirschsprung disease. Barium enema studies in lateral view show transition
zone (arrow ) with narrow rectum but dilated sigmoid colon.

Anorectal manometry to determine the presence or absence of relaxation of the
internal anal sphincter is helpful in establishing the neurogenic dysfunction of the
bowel. Barium enema studies and manometry are clearly complementary in the
diagnosis of Hirschsprung disease. However, rectal manometric studies are more
reliable than radiologic methods for short aganglionic segments that are usually
not apparent on barium enema studies. Manometric studies are not dependable in
infants younger than 3 weeks of age. If the barium enema and anal manometry