Some are sessile. More than one polyp can occur in different parts of the large intestine in the same patient but this is different from the polyposis syndromes. Microscopically, adenomatous polyp consists of compactly arranged glands larger than normal mucosal glands and with diminished mucin secretions. The nuclei are slightly hyperchromatic, stratified and display mitosis. The stalk is composed of normal mucosa including muscularis mucosae and submucosal tissue in continuity with the bowel wall.
Some polyps are partly glandular and partly villous.
Adenomatous polyp often shows dysplastic changes of various degrees in the glands near the surface. The villo-glandular pattern is usually seen in polyps larger than 1 cm and these show dysplastic changes more frequently. In the past, severe degree of dysplastic changes in the glands of the polyp were labelled carcinoma in situ. This term has now been abandoned because its usage at times leads to misinterpretation and unnecessary colectomies. Surgical pathologist must exercise caution in proper interpretation of dysplastic changes in adenomatous polyps.