A patient with a history of familial polyposis undergoes a diagnostic polypectomy. Which of the following types of polyps is most likely to be found?

Varying types of colonic polyps can be distinguished on pathologic examination. Adenomatous polyps are distributed throughout the entire large bowel, more commonly in the right and left colon than the rectum. They are often pedunculated and show an increased number of glands compared with normal mucosa. Although polyps that appear in familial polyposis are indistinguishable from single adenomatous polyps, they are manifested much earlier in life. Carcinomatous changes in patients who have familial polyposis occur approximately 20 years before carcinomatous changes of the bowel occur among patients in the general population.