Virtual Colonoscopy Can Be More Revealing, Study Finds

Virtual colonoscopy, an increasingly popular technique that uses CT scans instead of invasive endoscopy to identify colon polyps, can identify many medical problems outside the colon, making it a more valuable tool than researchers had previously believed.

In 500 men undergoing virtual colonoscopy, 45 had significant problems outside the colon, including aneurysms and cancers, researchers from UC San Francisco report today in the journal Radiology.

“We found that virtual colonoscopy can detect cancers and other conditions that would be missed with conventional colonoscopy with a negligible radiation risk, roughly comparable to that of a routine CT scan of the abdomen,” said the principal author, Dr. Judy Yee, a radiologist at UC San Francisco.

Although the American Cancer Society recommends that all Americans, even those without cancer histories in their families, be screened regularly for colon cancer beginning at age 50, less than 30% do, partly because of the length and discomfort of conventional colonoscopies.

Virtual colonoscopy -- in which doctors scan a patient’s colon with 20 seconds of X-rays -- is far less invasive than conventional colonoscopy, in which a patient is obliged to down a salty solution of laxatives before being sedated for a procedure in which a long flexible tube is inserted.

The study’s principal finding, Yee said, was that virtual colonoscopy was able to detect medical problems outside the colon that conventional colonoscopy didn’t address.

Of the 500 patients that Yee and colleagues screened at the San Francisco Veterans Affairs Medical Center using virtual colonoscopy, 8.4% were found to have “clinically important” lesions. These included eight kidney masses, seven lung nodules and four abdominal aortic aneurysms.

Twenty-five of the patients underwent additional imaging studies. Five ended up receiving surgical treatment to remove their lesions. The average cost of follow-up was $28.12 per patient, Yee said.

Typically, Yee said, these were patients who had no symptoms, so the lesions were caught at an early stage in which they were more amenable to treatment.

The report did not address the technique’s efficacy at detecting polyps, which Yee thought had been proved in previous studies.

The technique remains controversial.

“The high number of false positives is one reason why virtual colonoscopy might not be ready for prime time,” said David Brenner, a professor of public health and radiation oncology at Columbia University Medical Center.

“The procedure will definitely be a very big thing because it’s so much less intrusive than conventional colonoscopy. But the false positives are still a problem.”

Dr. William Boswell, a radiologist and associate professor of clinical medicine at USC’s Keck School of Medicine, said that “virtual colonoscopy in experienced hands, is probably as effective as conventional colonoscopy. But in inexperienced hands it’s not.” Five months ago, the American College of Radiology began a national trial in which 3,000 patients were being given both virtual and conventional colonoscopies. The trials, expected to be completed by February, “may well resolve the debate,” Boswell said.