A colon polyp is a growth of tissue on the inner lining of the large intestine, also called the colon. These growths are common, affecting about one in four individuals aged 45 and older. Polyps form when genetic changes disrupt the normal life cycle of cells in the colon lining, leading to an accumulation of abnormal cells. While the presence of polyps can be unsettling, not all will develop into cancer.
A Visual Guide to Colon Polyps
Colon polyps are primarily classified by their shape and how they attach to the colon wall. One common shape is pedunculated, which describes a polyp connected to the intestinal lining by a stalk. These are often described as having a mushroom-like appearance, with a distinct head and stalk.
Another primary shape is sessile, which means the polyp is flat and grows directly from the colon’s surface without a stalk. These polyps have a broad base and can be more challenging to detect because they are less prominent. A less common variation is the flat or slightly depressed polyp, which can be particularly difficult to see.
Beyond their external shape, polyps are categorized by their cellular structure, determined by microscopic examination. Adenomatous polyps, or adenomas, are the most common type, accounting for about 70% of all polyps found. Serrated polyps are another category, named for their sawtooth appearance under a microscope, and include the small and common hyperplastic polyps.
Understanding Polyp Characteristics and Cancer Risk
Adenomatous polyps are considered neoplastic, meaning they have the potential to develop into cancer. Although only a small percentage of adenomas become malignant, nearly all cancerous polyps begin as adenomas. The transition from a benign adenoma to a cancerous one can take many years. Villous adenomas, a subtype of adenoma, are more likely to become cancerous and are often sessile, making them harder to remove.
The risk associated with serrated polyps often depends on their size and location. Large, flat (sessile) serrated polyps located in the upper colon are considered precancerous. In contrast, small serrated polyps in the lower colon, known as hyperplastic polyps, are rarely malignant and are not considered a major concern for cancer development.
The size and number of polyps are also taken into account when assessing risk. Polyps larger than 10 millimeters, or having more than three polyps discovered, can indicate a higher risk for developing colon cancer. The specific cell type, such as a villous adenoma or a sessile serrated lesion, also contributes to a higher risk profile.
How Polyps Are Found and Removed
The primary method for detecting and removing colon polyps is a colonoscopy. During this procedure, a doctor uses a colonoscope—a long, flexible tube with a camera and light—to visually inspect the entire length of the colon. The instrument is inserted through the rectum, allowing the physician to identify polyps on the inner lining.
If polyps are found, they are often removed during the same procedure in a process called a polypectomy. Various tools can be passed through the colonoscope to perform the removal. One common technique uses a wire loop snare to encircle the base of the polyp and cut it from the colon wall.
After removal, the polyp tissue is sent to a pathologist for examination under a microscope. This analysis determines the polyp’s type, such as adenomatous or hyperplastic. The results help assess the cancer risk and determine the recommended schedule for future surveillance colonoscopies.