(Other names: polyps of the colon and rectum, or large bowel)
A colorectal "polyp" is a small finger-like or flat lump growing from the lining of the colon. There are many types of polyps, some of which are rare. The two most common types are adenomas and hyperplastic polyps.
The most important colorectal polyp is the adenoma, a small benign tumour growing to about 2 cm in size. Colonic adenomas are common, occurring in more than 20% of the population, and in the majority of patients there is no ill effect on health. They are more common with increasing age. There is good evidence that colonic adenomas are the early stage of colorectal cancer, although only a very small percentage of adenomas undergo malignant change and this process is very slow (e.g. five to 15 years). The larger the polyp, the greater the probability that the polyp will have undergone malignant change and contain cancer (adenocarcinoma).
Hyperplastic (or metaplastic) polyps are usually small, pale curved elevations of the colon lining. These are very common. Although hyperplastic polyps themselves do not turn into colorectal cancer, occasionally hyperplastic polyps (particular those which are large and multiple) will contain adenomas, known as mixed hyperplastic adenomatous polyps. In these polyps, development of cancer may occur but it is very rare.
Most patients with colonic polyps have no symptoms, and often polyps are detected at the time of investigation for unrelated symptoms. Where symptoms occur these are usually bleeding and sometimes pass mucous (especially large villous adenomas). Colonic polyps usually do not cause abdominal pain, diarrhoea, or constipation.
Colonoscopy is the preferred technique for diagnosis of colonic polyps because of its accuracy and because the polyp can usually be removed at the time of the procedure. A barium enema X-ray is an alternative, but is not as reliable. Colonoscopy may also fail to detect polyps depending on their size and location, quality of the bowel preparation, and the thoroughness of the colonoscopist.
Excision of colonic adenomas (polypectomy) and subsequent surveillance has been shown to reduce the long-term risk of colorectal cancer. In general, colonic polyps should be excised (cut out) in total rather that biopsied. Polyps are usually excised at colonoscopy by diathermy (heat) using a snare around the polyp base or by using a 'hot' biopsy forcep. All or part of the polyp is removed for examination by a pathologist. This allows the type of polyp to be determined and the presence of precancerous or cancerous change to be assessed. The risks of polypectomy should be discussed prior to the procedure. The major complications are bleeding and injury to the bowel wall, sometimes causing perforation. Death is rare. Polypectomy should have a complication rate of much less than 1 per cent (of patients) and complications need not be life threatening if detected and treated early. The benefits of polypectomy must be weighed against the risks, particularly in the elderly in whom tiny benign polyps are unlikely to cause any health problems and in whom complications are poorly tolerated. A small proportion of adenomas contain actual cancer. Removal of the polyp by colonoscopy is often sufficient treatment for such polyps provided the cancer is in a very early stage. If not, a surgeon would be asked to consider removing that section of the bowel to make absolutely certain that all the cancer has been removed. First degree relatives (parents, brothers and sisters, and offspring) of patients who have one or more colonic adenomas have an increased risk of colonic adenomas. The increased risk is related to the age of the patient (being higher where the patient is under age 60) and to the occurrence of colorectal cancer in additional relatives. In either of these circumstances it appears wise to recommend a colonoscopy in relatives who have reached the age of 40 years.
A technically unsatisfactory colonoscopy, or inability to remove all visible polyps, will require a repeat examination. If there are multiple or large (> 1 cm) adenomas it is common practice to re-examine the colon after 3 years (provided all adenomas were excised at the initial examination) and thereafter 5 yearly. If one small (< 3 mm) colonic adenoma is completely excised at the first examination, and tissue obtained confirming complete excision with no cancer or precancerous change, a repeat colonoscopy at 5 years is usually adequate, although some experts advise a colonoscopy at 3 years if there is also a family history of colorectal cancer. If no further polyps are seen at the time of a satisfactory repeat examination, the colonoscopy may then be repeated in 5 years. There is no need to continue these examinations beyond about age 75 - 80 years. Recommendations about screening intervals vary even amongst experts and the above intervals are guidelines. In patients with hyperplastic polyps there is usually no need to repeat the colonoscopy.
Colorectal polyps are most common in Western countries and are almost certainly related to lifestyle and diet, as well as genetic factors. However, there is no proven single dietary or environmental cause of colonic adenomas. Epidemiological studies suggest that a high intake of animal fat and red meat, and low intake of fibre, may predispose to colorectal cancer. While awaiting the results of large scale dietary intervention studies, patients can at least do no harm by modifying their diets to reduce these possible risk factors. There is some evidence that aspirin and non-steroidal anti-inflammatory agents such as sulindac reduce the risk of colonic adenomas, but this remains controversial.