What are colonic polyps?
A polyp is a medical term used to describe a rounded fleshy growth, which arises from the mucosa (internal lining of an organ. e.g. stomach or large intestine) or skin. In the gastrointestinal tract, polyps can be found in the large intestine, which is also known as the colon.
Colonic polyps are common, and their incidence increases with age. Colonic polyps are important because, over time, some of them may transform into a colon cancer.
What are the tests used to evaluate for colonic polyps?
The stool faecal occult, faecal immunochemical test (FIT) is used as part of screening at-risk individuals for colonic polyps and colorectal cancer.
Colonic polyps can be identified through a variety of tests, namely colonoscopy or CT colonography. Older tests such as the barium enema and guaiac faecal occult blood tests are no longer recommended, as their accuracy for detecting colon polyps and colon cancer is much lower.
A CT colonography utilizes a CT scanner to interrogate the large intestine. While a CT colonography is capable of detecting polyps that are 6mm or larger with a high degree of accuracy, the caveat is that small or flat polyps can be easily missed.
A colonoscopy is an examination of the colon with a flexible endoscope. The doctor performing the procedure is able to carefully inspect and resect any colon polyps that are found
What kinds of colonic polyps are there?
Colon polyps can be categorized into adenomatous polyps, hyperplastic polyps or sessile serrated adenomas. There exist other histological variants, which are infrequently encountered and will not be discussed in this article. Adenomatous polyps may be classified into tubular, villous or tubulovillous adenomas. Adenomatous polyps containing a villous pattern have a higher risk of transforming into a colon cancer.
Other high-risk features are a polyp size of more than 1cm, or a polyp with high-grade dysplasia. The term ‘high-grade dysplasia’ suggests that the cells are abnormal, and this is detected when the polyp is examined under a microscope. Polyps with high-grade dysplasia are pre-cancerous and can transform into cancer anytime. A sessile serrated adenoma is another type of colon polyp, which tends to be flat and spreads outwards as it grows. This type of polyp can be easily missed on CT colonography and faecal immunochemical tests. Like adenomatous polyps, a sessile serrated adenoma also has a risk of malignant transformation, and it needs to be resected.
Fortunately, not all polyps are cancerous. Hyperplastic polyps, which are commonly found in the colon, are non-cancerous. Hyperplastic polyps are often seen in the last part of the large intestine (rectum). They tend to be small, flat and pale looking and can be safely left alone. However, hyperplastic polyps which are large (> 1cm) or located in the proximal colon, near the small intestine can transform into a colon cancer. Often, it is impossible to ascertain whether a polyp is adenomatous, sessile serrated or hyperplastic based on its appearance during colonoscopy. Hence, it is recommended that all colon polyps should be resected, with the exception of hyperplastic-looking polyps in the rectum.
Scientific research has shown that colon polyps may take as long as ten years to transform into cancer. This transformation is called the adenoma-carcinoma sequence.
Colon polyps that are less than 1cm will not cause any symptoms. These polyps are often identified during CT colonography or colonoscopy. Large polyps may cause a change in bowel habit, diarrhoea, and anaemia from occult bleeding, or even frank bleeding during bowel movements.
What happens after the colonic polyps are found?
Of note, the primary aim of colorectal cancer screening is to identify individuals with colon cancer, and not polyps. Nonetheless, if polyps are detected during cancer screening, it should be removed, because the eradication of these polyps will mitigate one’s risk of colon cancer.
In addition, individuals with a history of colon polyps should be enrolled in a polyp surveillance program. The attending doctor should decide the timing of the subsequent colonoscopy, and it is influenced by the following factors:
In summary, colon polyps are a precursor to colon cancer. They are often detected during cancer screening. The resection of colon polyps can reduce an individual’s risk of colon cancer.
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