Overview of Colorectal Polyps
Colorectal polyps are abnormal growths that develop in the lining of the colon or rectum. A single polyp also is called a polypus, and the occurrence of multiple polyps is a condition referred to as polyposis. Some colorectal polyps are flat growths of tissue and others grow on a stalk or stem (called a pedicle). Colorectal polyps, also called intestinal polyps, are common in adults over the age of 50.
In most cases, colorectal polyps are slow-growing and benign (non-cancerous). They usually do not cause symptoms, but may cause rectal bleeding. In less than 1% of cases, intestinal polyps become malignant (cancerous). Multiple polyps and polyps larger than 1 cm in size have a higher risk for malignancy.
In addition to the colon and rectum, polyps also can develop in the mucous lining (mucosa) of other hollow organs and cavities in the body, including the following:
- Small intestine
Anatomy of the Colon and Rectum
The colon and rectum, which make up the large intestine, or large bowel, are part of the digestive tract. During digestion, the colon absorbs water, nutrients, and other substances from food and transfers them into the bloodstream.
The colon is located between the small intestine and the anus. It consists of the cecum (connects to the small intestine at the cecal valve), the ascending colon (vertical segment located on the right side of the abdomen), the transverse colon (extends across the abdomen), the descending colon (leads vertically down the left side of the abdomen), and the sigmoid colon (extends to the rectum).
The rectum is the last segment of the large intestine. Waste material (i.e., stool or fecal matter) is stored in the rectum until it is eliminated from the body through the anus. Colorectal polyps can develop throughout the large intestine, but they occur more often in the descending colon, the sigmoid colon, and the rectum.
Types of Colorectal Polyps
Hyperplastic polyps are benign growths that account for approximately 90% of all colorectal polyps. This type, which is characterized by the excessive growth of normal tissue, usually does not become cancerous (malignant).
Adenomas, also called adenomatous polyps, develop in surface (epithelial) cells in the intestinal lining (mucous membrane or mucosa). This type has a higher risk for developing into cancer.
Rarely, large hyperplastic polyps contain adenomas, which can be malignant. This type is called a mixed hyperplastic adenomatous polyp.
Incidence and Prevalence of Colorectal Polyps
Colorectal polyps are common, and incidence increases with age. Approximately 15–20% of all adults and 30% of people over the age of 50 in the United States have intestinal polyps. They are more common in Western countries, perhaps due to a diet that is high in animal fat (e.g., red meat) and low in fiber.
Men develop colorectal polyps slightly more often than women. Because African Americans are at an increased risk for developing colorectal cancer at a younger age, people of this race may also have a higher risk for colorectal polyps. Genetic (inherited) mutations found in some Ashkenazi Jews (i.e., Jews of Eastern European decent) may increase the risk for intestinal polyps and colorectal cancer.