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 weeks of age If the barium enema and anal manometry