A greatly enlarged colon that may be present at birth or develop later. It can occur in all age groups and the condition is typified by severe chronic constipation. Megacolon is caused by obstruction of the colon, possibly due either to faulty innervation, or to psychological factors. Other causes are HIRSCHSPRUNG'S DISEASE or ULCERATIVE COLITIS. In old people the persistent use of powerful laxative drugs may cause the condition.