Bowler hat sign
Pattern seen during radiologic examination
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The bowler hat sign is a radiologic sign seen on double-contrasted barium enema studies, indicating the presence of a colonic polyp.[1] A ring of barium collects at the base of the polyp and also along its dome, simulating the appearance of a bowler hat.[1] This sign is present for growths that are an intermediate between flat and pedunculated.[2] The differential diagnosis for this sign includes bubbles, diverticula, and unusual projections of anatomic structures such as the appendix.[2]