Solution: The findings on this study are that of a massive stool ball that fills much of the sigmoid and descending colon. There are several possibilities, but realistically the first thought in a patient of this age would be Hirschsprung disease. This is a condition that is characterized by lack of development of the parasympathetic ganglia in the large bowel. Since it is related to an arrest of migration in the craniocaudal direction, it can involve a variety of lengths of colon (short segment to entire colon). It occurs in about 1 in 5,000 live births and is diagnosed by a mucosal suction biopsy of the rectum. Imaging findings include: a transition point with reversal of the recto-sigmoid relationship (i.e. the sigmoid is larger in diameter than the rectum), sawtoothing within the rectum (seen on enema), severe constipation, and generalized bowel distention. We are used to seeing this on barium enema, but not on CT. Here is an image from the enema that is more typical of what we expect to see.