What Is a Colorectal Adenoma?

A colorectal adenoma is an abnormal growth of glandular tissue in the gastrointestinal tract. These growths can be diagnosed by colonoscopy, air-contrast barium enema, or computed tomography (CT) scan. They can be classified by their appearance to the naked eye and by their microscopic characteristics. Colorectal adenomas are treated by removing them, as there is a risk they can develop into cancer if left in the body.

Irregular growth of normal glands in the gastrointestinal tract results in a colorectal adenoma. In the gastrointestinal tract, the colorectal portion is a tube-shaped structure through which partially-digested food and waste products move. The part of the gastrointestinal system that contacts the digesting food is made of epithelial tissue. Under this epithelial tissue lies a variety of glands that produce substances important to the process of digestion. The abnormal proliferation of these glandular structures is what makes up the adenoma.

The diagnosis of colorectal adenoma is usually made by performing a colonoscopy. In this procedure, doctors insert a probe containing a camera through the anus in order to visualize the inner surface of the colon and rectum. Any tissue jutting out abnormally is removed during the procedure. It is then sent to a pathologist for microscopic analysis. Colorectal adenomas can also be detected by other imaging techniques, such as a CT scan or an air-contrast barium enema, but the colonoscopy offers the added benefit of being able to immediately remove the adenoma.

Removal is the proper treatment for a colorectal adenoma. The reason why removal is required is that approximately five percent of colorectal adenomas develop into colorectal cancer. If diagnosed by colonoscopy, the adenoma is removed as soon as it is seen. Patients who are diagnosed by other imaging methods require a follow-up colonoscopy to remove the adenoma. After removal, patients are monitored by having a repeat colonoscopy performed at least every five years.

Three types of adenomas can be seen during colonoscopy. They are named based on their structure and appearance. Sessile adenomas are structures with large, broad bases. Similar to sessile adenomas, flat adenomas also have large bases connected to the inner wall of the gastrointestinal tract, but these growths typically have a diameter at least two times longer than the height. Pedunculated adenomas are the third type, and are mushroom-shaped with a narrow stalk connecting the inner intestinal surface to the growth.

In addition to being classified by its appearance to the naked eye, a colorectal adenoma can be categorized according to its microscopic features. This determination is often made by a pathologist examining the adenoma after removal. One classification is a villous adenoma; in this subtype, the abnormal glands making up the adenoma have an elongated pattern. Tubular adenomas, another subtype, have glands with a branched structure. A combination of the two types of microscopic structures is described with the term tubulovillous.