Traditional or Virtual Colonoscopy?

The new virtual colonoscopy—a colon cancer screening technique that uses CT scans—is increasing in popularity and seems to be doing an admirable job of identifying polyps. In fact, in a recent study this procedure was found to detect 90 percent of large polyps that were 10 millimeters or more in diameter. That is the same accuracy that has been reported for colonoscopy itself in other studies conducted. The regular colonoscopy, however, is still able to detect polyps that are much smaller.

The findings of this study come from 15 community and academic medical centers that performed both the virtual colonoscopy and the traditional colonoscopy on approximately 2,600 patients that were ages 50 and older.

The leader of this study, C. Daniel Johnson, MD, and a professor of radiology at the Mayo Clinic in Scottsdale, Arizona, stated that the new study validates the new guidelines endorsing virtual colonoscopy as a screening option for colon cancer. "Up to now, there has been conflicting data on how good this test would be…. This is the largest study to date on CT colonography. The performance data shows the sensitivity is very similar to hat quoted for colonoscopy."

Johnson and his team have found that CT colonography could detect 78 percent of the polyps that were as small as 6 millimeters in diameter, but caught only 65 percent of the polyps that were 5 millimeters or smaller. Johnson notes in a news release from the American Gastroenterological Association that it is not exactly clear that leaving even small polyps is safe.

Polyps that are 10 millimeters or more progress into cancer at the rate of 1 percent annually. Polyps that are half that size should not progress into cancer any faster, however, the rate at which such smaller polyps progress is not known at this time. Johnson and his colleagues also noted that less than 2 percent of the polyps that are smaller than 5 millimeters have features that suggest that they are precancerous.

The downside of having the virtual colonoscopy is that it still requires that you go through the same bowel prep, which is the cleansing of the bowels, as the regular colonoscopy.

Dr. Robert Fletcher, which is a professor emeritus at Harvard University, says that one of patient's biggest complaint about the colonoscopy is the prep and not the procedure itself. "Nobody ever said the prep was easy, and it is just the same for the CT colonography as it is for colonscopy. "And if the scan finds something in the colon, which it does about 17 percent of the time, you have to turn right around and get prepped again and have a colonoscopy, unless it can be arranged the same day."

Johnson states that the centers that are performing CT colonography should be equipped to offer same-day colonoscopy for the patients who need it. Fletcher states that it is very important for patient's to ask about this before they choose to go with the virtual colonoscopy as their screening option.

The virtual screening colonoscopy as about a 14 percent false-positive rate. That is not too bad, but considering that it's a screening test that is designed to catch as many polyps as possible. However, the patients that get a false alarm will unfortunately have to undergo an unnecessary colonoscopy.

A greater concern for Fletcher is the fact that the CT scans can see more of the body than just the bowels. The scans detected problems that were serious enough to got for further test or urgent care in 16 percent of the patients in Johnson's study.

Fletcher stated that it is not trivial for your physician to tell you that he found something in your kidney or on your adrenal gland. The odds are actually pretty low for being able to help people for those things that are outside the colon and there is also the worry and the bother of having additional tests and finding additional things that are wrong that you never knew about but can't be changed now that you know about them.

However, Johnson has a view that is completely different on this issue. Johnson states that the regular colonoscopy can't look outside the colon, but the new CT colonograpy does. So this leaves the opportunity among patients that are age 50 and older to be able to look for other abnormalities that could be asymptomatic but may cause harm to them in the future. We can also look for aortic aneurysms in the abdomen and tumors in other parts of the body.

This year, the American College of Radiology, the U.S. Multi-Society Task Force on Colorectal Cancer, and the American Cancer Society added the CT colonoscopy to the list of their colon screening options.

The American Gastroenterological Association noted that only half of the patients get recommend colon cancer screening, and that the virtual colonoscopy could improve this horrible statistic.

Dr. David A Margolin, director of colorectal surgery research at the Ochsner Clinic Foundation in New Orleans, says that GI doctors are not yet ready to embrace the new CT colonography. "CT colonography will, in the future, play a role in colon cancer screening," Margolin said. "At centers of excellence, at a very few centers where the quality of software and the CT engineer and excellent radiologist training all converge, it is useful. But if you expect these kinds of results at very community hospital, you won't get it."

Johnson  admits that most radiologists are required to have specialized training and experience before they are ready to perform screen CT colonography. But he also says that this kind of training is readily available.

Johnson also notes that this study purposely included the community hospitals and a wide range of different CT equipment and software to simulate what could happen when the virtual colonoscopy becomes more common.

"We spend a lot of time training and testing our CT colonography readers. It does require a special skill set." "These are good questions for patients to ask their radiologist: How many CT colonographies have you read? How much training have you had? Radiologists who avail themselves of this training can get the same results we report."

If you would like more information on this study, the study conducted by Johnson—and Fletcher's editorial comments—will appear in the September 18 issue of The New England Journal of Medicine.