Bowler Hat Sign

• A sign usually attributed to a polyp of the colon which is midway between a flat plaque and a pedunculated polyp causing the appearance of a bowler hat on double contrast barium enema examinations
• Miller et al described a method of differentiating a “bowler hat” caused by a diverticulum versus one caused by a polyp
• If the bowler hat points toward the lumen, it represents an intraluminal structure (ie, a polyp).
• If, however, it points away from the long axis of the lumen, it represents an extraluminal structure (ie, a diverticulum).
• Only if the bowler hat is located in the midline or is directly parallel to the long axis of the bowel is it impossible to classify the abnormality as a polyp or a diverticulum
• The sign might be visible in other parts of the GI tract on double contrast examinations

 Bowler Hat Sign. A sessile polyp is seen along the anterior border of the rectosigmoid (white arrow) with a slight rim of contrast at its base. The bowler hat points towards the lumen which favors a polyp.

Bowler-hat sign: a simple principle for differentiating polyps from diverticula. WT Miller WT Jr, MS Levine, SE Rubesin and, I Laufer. Radiology. 1989 Dec;173(3):615-7.