Adenomatous polyps are neoplastic colorectal polyps composed of dysplastic epithelium. They are common, with an incidence of approximately 60-70% by age 60. These polyps are most common in societies with a high incidence of colorectal cancer, and are the precursors of colorectal adenocarcinoma.
Adenomas can be sessile or pedunculated, and can also be classified according to their architecture as tubular, villous or tubulovillous. Tubular adenomas are almost always (95%) <2 cm in size and usually have smooth surfaces and a pedunculated architecture. Villous adenomas are sessile with a shaggy cauliflower-like appearance and are usually bigger than tubular adenomas (>50% >2 cm in size). Tubulovillous adenomas have features intermediate between tubular and villous adenomas.
The vast majority of colorectal adenocarcinomas (colon cancers) arise from adenomatous polyps. The risk of an adenoma containing adenocarcinoma depends on the type of polyp and its size. 1% of tubular adenomas <1 cm in size contain adenocarcinoma, compared with 10% of similarly sized villous adenomas. 10% of tubular adenomas 1-2 cm in size contain adenocarcinoma. 35% of tubular adenomas >2 cm in size contain adenocarcinoma, compared with >50% of similarly sized villous adenomas.
When they are found, adenomas are removed endoscopically, and patients are followed periodically with colonoscopy. Polypectomy may suffice for polyps with cancer within them, or the patient may require formal segmental colonic resection.
If an individual has many (>100) polyps, they may suffer from familial adenomatous polyposis (FAP).