Definition of terms
During the normal course of a person’s life, sections of the colonic mucosa may change in appearance and develop what are usually benign growths on the surface of the colon. These growths are known as polyps and can be completely harmless (hyperplastic polyps). Other types of polyps may be more prone to undergoing further changes and may, in time, become malignant (adenoma). As these types of polyps have the potential to become cancerous (adenoma-adenocarcinoma sequence), they should be detected early and removed. This can usually be accomplished as part of a colonoscopy procedure, thus eliminating the need for additional surgical procedures. Although other types of polyps exist, these are mostly benign in nature. Once a tissue sample has been taken, a pathologist can examine the precise features of the polyp in question and determine what type of polyp it is. This classification is essential in determining the nature of further treatments and follow-up examinations. There are also a number of hereditary conditions that are associated with the development of large numbers of polyps. Patients with this type of condition will require extremely close monitoring.
Some of the more significant types of polyps (here adenomas) develop as a result of hereditary conditions, and we now fully understand the exact molecular mechanisms (down to the smallest particles) involved in the step-wise sequence from adenoma to malignancy. Size and histologic type also play a significant role in whether a polyp is likely to turn malignant, as do age, diet, lifestyle (smoking, level of exercise) and weight.
Frequency of occurrence
Preventive screening tests lead to the detection of polyps in up to 20% of asymptomatic patients. In patients over the age of 50, this figure can be as high as 35%, with adenomas (intraepithelial neoplasia) accounting for 50-75% of all polyps found. Although the majority of such lesions are under 1 cm in size, up to 10% of them are found to be bigger than 1 cm, and just less than 1% as having become malignant (carcinoma). This is of course also dependent upon the shape of the polyp (sessile/flat or pedunculated, with a narrow or a broad base).
Only approximately 10-25% of adenomas can be detected using commonly available stool tests. While conventional colonoscopy and invendoscopy have the highest adenoma detection rates, they miss up to 15% of polyps smaller than 1cm in size (inadequate bowel cleansing, high colonic motility, insufficiently thorough examination, time pressure). Detection rates for capsule endoscopy are slightly lower, with those achieved by CT colonography or MRI-based colonography lagging even further behind. All of these screening methods require patients to undergo thorough bowel cleansing.
The majority of polyps can be removed as part of a normal colonoscopy procedure. This involves the use of special tools that are introduced into the colon via the endoscope’s insertion tube. Resection and removal of the polyp is achieved by using small cutting forceps or wire loops (an electrical current is used to cauterize the polyp). If the procedure results in larger wounds, these can be closed using endoscopic clips. Only in very rare cases (size, location, malignant changes in resected polyps) will it become necessary for patients to undergo surgery. Although capsule endoscopy and imaging technologies are useful tools in terms of the visualization of polyps, they cannot be used for their removal.
Depending on the patient’s genetic predisposition (parent or siblings with a history of colon polyps or colon cancer), the number and size of any polyps detected, and the patient’s need for reassurance, follow-up investigations should be spaced at between one year and a maximum of 10 years apart. In the majority of cases, follow-up examinations are conducted every 3 to 5 years. Patients with an endoscopy-based diagnosis of colon polyps should undergo follow-up endoscopies. Stool tests tend to be unable to provide any useful results.