The bowler hat: a valid sign of colonic polyps?

Diagnosis of colorectal neoplasms at double-contrast barium enema examination

The double-contrast barium enema examination has been recognized as an option for colorectal cancer screening in Americans with average risk who are greater than 50 years of age. The purpose of this article is to review the principles for diagnosing colorectal neoplasms on double-contrast images and the spectrum of findings associated with these lesions. Colonic polyps can be sessile or pedunculated; their appearance depends on whether they are located on the dependent or nondependent wall of the bowel. Villous tumors may be flat, lobulated lesions, also known as "carpet" lesions, that are characterized by a finely nodular or reticular surface pattern, without a discrete mass. Colonic carcinomas may manifest as plaquelike, polypoid, semiannular ("saddle") or annular lesions. Colonic neoplasms sometimes are more difficult to detect in the region of the ileocecal valve or the distal rectum or in patients with severe diverticulosis. Careful double-contrast technique and meticulous scrutiny of the images therefore are required to optimize detection of these lesions.