Virtual Colonoscopies Virtually as Effective as Standard Scans

By Anastacia Mott Austin

A comprehensive study involving 15 medical centers and 2600 patients has shown that performing a "virtual" colonoscopy – a screening involving a CT scan – is nearly as effective at detecting medium and large sized colon polyps as the more invasive internal test that is usually performed.

The researchers found that the virtual scan was able to detect tumors of 10 millimeters or greater 90% of the time.

This is promising news for the field of colon cancer research and prevention. Many people avoid what they see as an invasive procedure; the current technology for a colonoscopy involves a catheter with a camera on it being inserted through the anal cavity.

The virtual scans do not require this step. However, patients must still undergo the unpleasant preparatory step of thoroughly cleansing the bowel before the procedure. Many people report that the preparation for a standard colonoscopy is more unpleasant than the procedure itself.

Oncologists say that the virtual scan may encourage more patients to undergo colon cancer screening, which will ultimately improve survival rates for the most common cancer in America. The virtual test is just about as effective.

"Up to now, there has been conflicting data on how good this test would be," said Dr. Daniel Johnson, radiology professor at the Mayo clinic in Scottsdale, Arizona, to reporters at WebMD. "This is the largest study to date on CT colonography. The performance data shows the sensitivity is very similar to that quoted for colonoscopy."

Most insurance plans do not currently cover the virtual scans, but this is changing. Major insurance companies are reviewing the results and the cost effectiveness of the CT scan technology. The virtual scans are less costly and less invasive than standard tests, and if these initial results stand up over time, insurance companies will be expected to cover the procedure.

One additional benefit, says Dr. Johnson, is that the virtual scan can sometimes detect problems in other areas of the body, like the kidneys, that would otherwise have gone unnoticed until later. "Colonoscopy cannot look outside the colon. CT colonography does," said Dr. Johnson to reporters. "So there is an opportunity among patients age 50 and older to be able to look for other abnormalities that may be asymptomatic but may cause harm in the future. We can look for abdominal aortic aneurysms and tumors in other body parts, [for example]."

There are some downsides, however. The virtual scans are not as effective in detecting smaller polyps or flat lesions in the colon, being accurate only about 65% of the time with smaller tumors (defined as five millimeters or smaller).

And as mentioned, the unpleasant preparatory laxative drink or pills must still be taken, in order to clear the area for viewing.

In addition, some doctors are concerned about radiation levels contained in CT scans. While they are generally lower than x-rays, any procedure that involves radiation can have a cumulative effect on the body.

Experts caution that the technology may not be available in every area for a few years, as CT and radiation techs must get the necessary training to be able to properly view the scans and accurately detect problems without an unnecessarily high number of false positives (which would require a patient to then undergo a standard colonoscopy procedure).

Still, virtual scan colonographies are a step in the right direction, say many doctors.

Dr. David Lichtenstein, director of endoscopy at Boston Medical Center, said to reporters, "Traditional colonoscopies remain the gold standard, but virtual colonoscopies are a good alternative."