‘Virtual’ colonoscopies found good at detection

“Virtual” colonoscopies are about as reliable as more invasive procedures for finding cancer and polyps, according to the largest study of its kind, published in today’s New England Journal of Medicine.

The study of 2,600 adults found that virtual exams – which use CT scans, or computed tomography – found 90 percent of patients with cancer or polyps, which are raised growths that sometimes become malignant. The study, performed at 15 centers around the country, confirms the results of smaller trials.

Another study in the same journal shows that people who have normal results from a traditional colonoscopy – in which a lighted scope is guided through the colon – can safely wait at least five years before repeating the test. Patients with abnormal results usually need exams sooner.

The studies can give people greater confidence in following the advice of groups such as the American Cancer Society, which recently added virtual colonoscopy as one of its recommended screening options, says Robert Fletcher, professor emeritus at Harvard Medical School, who wrote an accompanying editorial. Fletcher notes that the cancer society already recommends that people who have normal results from a traditional colonoscopy get rechecked after 10 years.

The new studies may give some doctors and patients more confidence in the virtual option, Fletcher says. He says he hopes that the research will persuade doctors and patients to wait at least five years after a normal exam before repeating the test. Today, Fletcher says, some doctors are screening patients much more frequently.

The American Gastroenterological Association, whose members perform traditional colonoscopies, says that exam is still the gold standard because doctors can both detect and remove polyps during one procedure. But the new study shows that virtual colonoscopies are a good way to increase the number of people who undergo screening, society president Robert Sandler said in a statement. Today, only about half of eligible patients have any colorectal screening.

The gastroenterological society notes that virtual colonoscopy has limitations:

•In the new study, the scans found only 65 percent of small polyps. Doctors don’t know how well CT scans find flat lesions.

•Patients are still required to undergo bowel preparation – something that’s often considered the most unpleasant part of the procedure.

•Doctors can’t cut out polyps during the CT scans. Patients with polyps will have to undergo a second, conventional colonoscopy to remove them.

Experts say both procedures have risks. Patients who have traditional colonoscopies sometimes suffer bowel perforations. Undergoing virtual colonoscopies every five years or so could expose patients to a “substantial” dose of radiation, Fletcher says.