What does plain radiographic study of the abdomen reveal in large bowel obstruction?
A large bowel obstruction demonstrates differential air-fluid levels (stair steps) of the small intestine or a massively dilated colon. The colon is identified by the presence of haustral folds, compared with the valvulae conniventes of the small intestine. The rectum is usually gasless, although gas distal with a colonic obstruction may not have completely cleared the distal colon. A picture resembling small bowel obstruction (SBO) alone may appear in a very proximal colon obstruction. Colonic pseudoobstruction also may give a roentgenographic picture similar to true obstruction.