Adenomatous Colorectal Polyps

The term colon polyp refers to a protuberance into the lumen from the normally flat colonic mucosa. The different types of colon polyps are referred to as being either non-neoplastic polyps or neoplastic in nature. The non-neoplastic colon polyps include hyperplastic polyps, mucosal polyps (with normal mucosal histology), and inflammatory pseudopolyps. Submucosal lesions may have a polypoid appearance, arising either from a benign lesion, such as a lipoma, hemangioma or fibroma, or from a carcinoid tumor or metastatic lesion.

Juvenile polyps are hamartomatous in nature and are generally considered non -neoplastic, although they can grow to become quite large and result in bleeding, abdominal pain, and even bowel obstruction. Hamartomatous polyps are commonly seen in patients with Peutz- Jeghers syndrome and they not only result in bowel symptoms, they also occasionally undergo malignant transformation. Adenomatous polyps, also called adenomas, are the most common form of colonic polyps, accounting for two-thirds of all colon polyps. They are neoplastic in cature and can develop into an adenocarcinoma of the colon or rectum. They are the most clinically significant colon polyp and will be the focus of the remainder of this article.

Colorectal adenomas are quite common, especially in western countries where the prevalence of colorectal cancer (CRC) is relatively high. While found in only 1–4% of men and women in their 20s and 30s, the incidence of adenomas increases with age, with adenomas found in 25–30% of Americans by 50 years of age and in up to 40–50% of individuals 70 years of age and older.¹ Adenomas are more common in men than in women, and more common in black men and women than in white men and women.² They are distributed throughout the entire colon and rectum; however, they tend to have a more proximal or rightsided colon distribution in women and a slightly more distal distribution in men. Proximal adenomas also appear to be relatively more common in African-Americans.³

Aging is a major risk factor for the development of colonic adenomas, as it is rare to find adenomatous polyps in individuals under 20 years of age. The exception is in patients with a hereditary adenomatous polyposis syndrome. Patients with familial adenomatous polyposis (FAP) syndrome sometimes develop colon adenomas during the first decade of life, whereas in patients with attenuated FAP (AFAP) or MYHassociated polyposis (MAP), multiple adenomas may appear during the third and fourth decades of life. A number of other factors increase the risk for adenoma development, including a family history of polyps, a personal history of polyps or inflammatory bowel disease, smoking or former smoking, drinking two or more alcoholic beverages a day, a diet high in animal fat, and being overweight or obese. By contrast, the risk is reduced with smoking cessation, limiting alcohol intake, taking regular exercise, calcium supplementation, and consistent aspirin or related anti-inflammatory drug use.