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The CT examination shows a markedly dilated colon. The rectum however is not dilated. The point of transition seems to be a mesenteric swirl at the level of the promontorium. This is best appreciated on the coronal series.
Somewhat confusingly, in this case the sigmoid loop is found in the right side of the abdomen, lateral to the cecum which has been relocated to the midline and actually slightly to the left.
Subsequent barium enema shows the characterestic beak sign, localized at the same point as the mesenteric swirl. Once this point could be passed, there was an instant evacuation of feces and gas from up to obstructed sigmoid.