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Is Virtual Colonoscopy a Suitable Alternative?


Oct. 13, 2008 – CT colonoscopy, also called virtual colonoscopy, has gained popularity as a screening tool for colon cancer. A recent study measured the procedure’s effectiveness against the standard colonoscopy procedure. Gastroenterologist Dayna Early, MD, discusses the results of the study and weighs the pros and cons of the new procedure.

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On this edition of Cancer Connection, we’ll talk about virtual colonoscopy and a new study that says it has comparable accuracy to traditional colonoscopy in some cases.

Host: Thanks for downloading this podcast from the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine in St Louis. I'm Jason Merrill. The topic of virtual colonoscopy or CT colonography is a popular one, with many patients looking for alternatives to traditional colonoscopy. While the radiological procedure has some limitations and is only covered by insurance, in most cases, when medically necessary, headlines about a new study touting the procedure’s accuracy made news. To talk with us more about this study is Dr. Dayna Early. She is a gastroenterologist at the Siteman Cancer Center. Dr. Early, thank you for joining us.

Early: Thank you, Jason. I’m happy to talk to you about this.

Host: Let's start at the beginning. What is CT colonography, or virtual colonoscopy?

Early: It's a type of a CT scan where the colon is imaged in a particular fashion with a certain software designed to look at the colon. And additionally, patients who have CT colonography also have imaging of their abdominal and pelvic organs, similar to a standard CT.

Host: Conversely, what is a regular colonoscopy, or traditional colonoscopy?

Early: So what we call conventional colonoscopy is where a light and flexible tube is passed into the rectum and passed around the colon. The colon is directly visualized with the electronics in the scope.

Jason: What are the differences between the two for the patient?

Early: Well, right now patients have to take a bowel prep for both exams. One of the differences is that CT colonography does not involve sedation, whereas conventional colonoscopy does. The other significant difference is that CT colonography is not a procedure in which polyps can be removed, whereas in conventional colonoscopy, when polyps are identified, they can be removed right then.

Jason: There’s a study that came out recently from the American College of Radiology Imaging Network that was a national CT colonography trial that the Siteman Cancer Center was part of. What were the findings of the trial comparing the CT colonography and conventional colonoscopy?

Early: So what the study showed was that CT colonography – as compared to conventional colonoscopy as the gold standard – detected polyps a centimeter or greater in 90 percent of patients. The study was designed so that polyps 5 millimeters or less were not commented on, so we don't know the accuracy of CT colonography in detecting these polyps. Polyps between 5 millimeters and 10 millimeters, or a centimeter, had increasing rates of detection with CT colonography, starting at about 80 percent with 6 millimeter polyps and going up to 90 percent for 10 millimeter or greater polyps.

Host: So, it found that virtual colonoscopy and standard colonoscopy were comparable in accuracy?

Early: They're comparable in accuracy for polyps that are a centimeter or more. One of the reservations that gastroenterologists have is that CT colonography is not as accurate as colonoscopy at detecting polyps 6 to 9 millimeters, and these polyps can actually harbor precancerous changes or even cancer. And additionally, CT colonography doesn't even comment on polyps that are 5 millimeters or less, and these are lesions that we frequently can see with conventional colonoscopy and remove for histology.

Host: You touched on that earlier. With a regular colonoscopy, if a polyp is found, you can take it off on the spot.

Early: That's correct. So my view of this is that any time we have a test that will increase compliance with colorectal cancer screening, I think we should be optimistic. I do think that CT colonography primarily should be used for patients at average risk for whom it's unlikely that a polyp will be found. If patients have any risk factors that put them above average risk for having a colon polyp, then my opinion is they should proceed directly to conventional colonoscopy so that if a polyp is found, it can be removed right away and they don't have to undergo two procedures

Host: Dr. Early, thank you for joining us.

Early: Thank you, Jason.

Host: For more information about colon cancer, you can visit the Siteman Cancer Center online at, or to find out your colon cancer risk, you can visit Thanks for downloading. Until next time, I'm Jason Merrill.