This slide demonstrates normal sigmoid colon. This enable the endoscopist to see lesions just inside the anal canal which can be easily missed otherwise. The most common types are hyperplastic, tubular, and villous. This slide shows a hyperplastic polyp on top of a mucosal fold. They are entirely benign when biopsied.
Tubular adenomas are much less likely to develop cancer than are villous adenomas.
Most adenomas under 2 cm can be removed endoscopically. This rectal villous adenoma shows superficial central ulceration suggestive of malignancy. Of all villous adenomas, one third are benign, one third have carcinoma in situ, and one third will demonstrate invasive carcinoma. In addition to the effect of histologic type on the development of cancer, the size of a polyp is also important. Polyps greater than 2 cm are much more likely to become malignant.