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A colorectal polyp is an abnormal growth of cells arising from the inner lining of the large intestine (colon and rectum). This is seen as a lump protruding into the bowel lumen. Some appear as a flat protrusion while others appear as rounded lumps or may have a narrow stalk (like a mushroom). It is common for someone to have colorectal polyps as around 20% of people above the age of 50 have colorectal polyps.
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Most colorectal polyps are benign. Broadly, colorectal polyps are divided into pre-cancerous polyps and hyperplastic polyps. It is difficult to differentiate between pre-cancerous polyps and hyperplastic polyps visually and that is why all polyps are removed whenever possible.
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Pre-cancerous polyps are classified as dysplastic (also called adenoma or serrated polyp) or hamartomatous. Dysplastic polyps are the most common type of polyps and up to 10% of dysplastic polyps may become cancerous in the future. Some dysplastic polyps already contain cancerous cells when diagnosed, especially the larger ones. In fact, about 30% of polyps greater than 2 cm contain cancerous cells.
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Hamartomatous polyps are rare and usually present as part of a genetic disorder such as Peutz-Jegher’s disease. The risk of cancerous change in hamartomatous polyps is less than dysplastic polyps.
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Most polyps are asymptomatic as they are small (< 1 cm). Occasionally, some polyps grow to a few centimeters in diameter and may cause bleeding, mucus discharge or even abdominal pain.
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The best method of diagnosis is colonoscopy. This involves inserting a camera-tipped flexible tube through the anus to visualize the inner lining of the colon and rectum. Any polyp detected is removed immediately using electrocautery.
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When a colonoscopy is not feasible, the alternative is either CT colonography or barium enema. Both these tests use x-rays but do not allow the doctor to remove the polyps upon diagnosis.
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Polyps once removed will never recur. However, new polyps can appear in another part of the colon. A person who has been found to have pre-cancerous polyps in the colon is 8 times more likely to develop a new polyp in the colon than a person who did not have polyps.
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The timing of a repeat colonoscopy depends on the risk stratification of the patient. Patients who have more advanced polyps, greater number of polyps or stronger family history of colorectal cancer may need earlier review. In general, your doctor may advise repeat colonoscopy between 1 to 3 years later. It is believed that most polyps take up to 10 years to change from a polyp into cancer.
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