This is a classic example of a polypoid lesion, demonstrating a persistent defect on multiple images.  Hyperplastic polyps are thought to present no increased risk of malignancy.  Adenomatous polyps occur in 10-30% of the adult population and also increase in incidence with age.  When these polyps are less than 5 mm, the incidence of cancer is 0.01%.  This rate increases to 30% when the polyp reaches a size of 2 cm or greater.  These two types of polyps are radiographically indistinguishable on barium enema. 

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