Bowler hat sign

Last revised by Daniel J Bell on 12 Dec 2021

The bowler hat sign refers to an appearance on a GI contrast study, which may be seen with both polyps and diverticula of the bowel. The filling defect produced by the pathology mimics the outline of a bowler hat. It was originally described for colonic lesions, but can be seen with lesions throughout the GI tract. 

The orientation of the bowler hat helps differentiate between the two conditions. When the top of the bowler hat is directed towards the center of the long axis of the colonic lumen it is a polyp. When the bowler hat is directed away from the colonic lumen it is a diverticulum 2. Rarely, the bowler hat is oriented along the colon long axis, in which case this differentiation is not possible.

History and etymology

The bowler hat sign was first described to help distinguish colonic polyps from intraluminal foreign bodies by James E Youker, an American radiologist, and Solve Welin, a Swedish radiologist, in 1965 1.

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Cases and figures

  • Figure 1: bowler hat
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  • Case 1: gastric polyp
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