Polyps in large bowel grow for many years before they become cancer. How big a polyp can grow before it becomes a colon cancer? Is it important to remove all polyps found during colonoscopy? How CT colonography can identify important polyps in large bowel? Leading virtual colonoscopy screening expert discusses CT colonography. Virtual colonoscopy.

Screening for colon cancer is the best method to prevent deaths from colorectal cancer. Screening by virtual colonoscopy looks for polyps in the large bowel. How does size of the polyp matter for colorectal cancer screening? What is the significance of different types of polyps for colon cancer diagnosis? Specifically, what is a flat lesion adenoma? Dr. Perry Pickhardt, MD. It turns out, size is actually everything in terms of polyp importance. We call smaller colon polyps, 5 millimeters and less, "diminutive lesions". They do not have any clinical significance, they have almost zero chance of being cancer. They are far too common in the population to be aggressively removed. Dr. Perry Pickhardt, MD. Because the cost and complications from smaller polyp removal will skyrocket. It would be as if you were to remove every mole from everyone's skin. It is just an impractical approach. Large polyps 10 millimeters and larger are important. The vast majority of these advanced adenomas have large size. Dr. Perry Pickhardt, MD. Larger polyps are clearly the target for screening and prevention. That leaves the gray zone of 6 to 9 millimeter size polyps. Dr. Anton Titov, MD. There is some controversy. We perhaps should aggressively pursue these benign polyps. 6 to 9 mm polyps are a little more common than large polyps. But they are not nearly as common as the tiny diminutive polyps. Dr. Perry Pickhardt, MD. There is some controversy there. In our practice, we advise that all large bowel polyps 6 millimeters and greater are to be removed by colonoscopy. But most patients actually choose to follow those polyps at a three year intervals. They wait for the rare case where such polyps grow to one centimeter or greater. Flat polyps, flat adenomas, is a very important subtopic. Dr. Anton Titov, MD. It has gained a lot of attention. It is a little confusing but flat polyps are difficult to detect relative to the obvious pedunculated or sessile polyps. These polyps that protrude well into the lumen of the large bowel. That is always been a consideration how to identify flat polyps better. But fortunately flat adenomas are much less aggressive on average. Flat adenomas grow very slowly. We have a lot of time to detect flat adenomas in large bowel at follow up of patients. With care, with good technique, both regular optical colonoscopy and CT colonography can detect flat polyps and flat adenomas fairly well. Although flat adenomas will be less conspicuous. Dr. Perry Pickhardt, MD. We have seen repeatedly that flat lesion detection rate by virtual colonoscopy has been excellent and similar to optical colonoscopy. We have a scientific article now that will be published soon. It is looking at serrated polyps in the right colon with CT colonography detection. We show that virtual colonoscopy has very good success for detection of serrated polyps. We now recognize serrated adenomas as a second pathway to colon cancer. Maybe 10 or 15% of colon cancers are arising from these right-sided "serrated lesions". Serrated adenomas tend to be flat lesions. Dr. Perry Pickhardt, MD. The good news is we can detect these serrated lesions with CT colonography with very good accuracy. It is a confusing topic. Dr. Anton Titov, MD. Because some people have jumped to the conclusion that flat adenomas are more aggressive. But actually the opposite is true. We take flat adenomas very seriously. But we know that time is on our side with these flat lesions, in general. CT colonography is able to detect flat polyps as well if not better than the traditional optical colonoscopy. Yes, it is interesting, and virtual and optical colonoscopies are probably complementary. But it appears that optical and virtual colonoscopies are comparable. CT colonography maybe has a slight advantage in some cases. There are other cases I have seen. Then optical colonoscopy might detect a lesion that was difficult to detect by CT colonography. They probably are complementary. Dr. Perry Pickhardt, MD. We haven't fully worked it out. But because of the oral contrast we give to patients who undergo virtual colonoscopy. It coats these polyps and coats the surface of the flat lesions. It serves as a beacon for detection at CT colonography. Dr. Anton Titov, MD. It is actually a very useful method for us to detect flat lesions in bowel. How often do you need to be screened for colorectal cancer? CT colonography or virtual colonoscopy is one of the best tests to find early colon cancer in time for cure. Colon Cancer Screening Guidelines recommend screening every 5 to 10 years. After 50 years of age. Colon cancer screening. Weighing the options is important. But regular screening must be done. Precancerous colon polyps – flat adenoma polyp. How big a colon polyp can grow before becoming a cancer threat? What is “flat adenoma”? Virtual colonoscopy (CT Colonography)can detect more rare large bowel and rectal lesions. Flat adenoma and serrated adenoma are two precancerous lesions in large bowel. Smaller than 5 millimeter polyps have basically zero chance of being colorectal cancer. Virtual colonoscopy is very good at detecting those polyps that have a chance to be early colorectal cancer or precancerous lesions. large polyps 10 millimeters or one centimeter and larger are important in screening for colorectal cancer. 6 to 9 mm polyps are in a grey zone for colon cancer risk. 6 to 9 mm polyps are more common than large polyps. both regular optical colonoscopy and CT colonography can detect flat polyps (flat adenomas) fairly well.