The mother of a 4-year-old child notes blood when laundering his underwear. Physical examination reveals a rectal mass. On proctoscopy, there is a smooth-surfaced, pedunculated, 1.5-cm polyp. It is excised and microscopically shows cystically dilated crypts filled with mucin and inflammatory debris, but no dysplasia. What is the most likely diagnosis?

Juvenile polyps are the most common form of a hamartomatous polyp. Singly they are likely to be sporadic, and the only complication is rectal prolapse; but when multiple polyps are present, they may be the result of an autosomal dominant syndrome with risk for development of adenocarcinoma. The remaining choices include polyposis syndromes unlikely to appear at this age.