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megacolon meg·a·co·lon (měg'ə-kō'lən)
Extreme dilation and hypertrophy of the colon.
massive enlargement and dilation of the large intestine (colon). The two main types of the syndrome are congenital megacolon, or Hirschsprung disease, and acquired megacolon. In congenital megacolon, the lowermost portion of the large intestine is congenitally lacking in normal nerve fibres; thus, peristalsis, or involuntary contractions, of the muscles of this part of the intestine cannot occur, and the bowel's contents are not pushed onward. The area of normal intestine above the abnormal part works harder to push on the fecal contents, with the result that the muscular walls of that part of the intestine become enlarged and thickened. The entire colon eventually becomes thick and distended. The symptoms of congenital megacolon include a distended abdomen and severe constipation in infants born with the disorder.