Inside out

Invented 16 years ago by a radiologist,virtual colonoscopy has become an increasingly popular alternative to standard,or optical,colonoscopy typically performed by a gastroenterologist. Initially regarded as a high-tech novelty,the new procedure has received key endorsements as a first-line screening test from influential medical groups after several studies found it to be effective at finding large polyps. Like other mass screening tests,including mammography,the overarching question is whether the benefits of virtual colonoscopy outweigh the risks.

Its supporters tout virtual colonoscopy as a more palatable alternative that has the potential to boost low rates of screening. Colon cancer can be prevented — or even cured — if detected early. “This is a really good test that’s going to find way more cancer than optical colonoscopy,” said Mark Klein of Washington Radiology Associates,who has performed more than 1,200 virtual colonoscopies since 2002. “Is it perfect? No. But no test is.”

The prospects for significant expansion of the procedure—covered by a growing number of insurance companies—have collided with an unexpected roadblock. In February,officials at the Centres for Medicare & Medicaid Services (CMS) announced a preliminary decision not to cover the procedure as a mass screening test for Medicare recipients.

CMS officials,scheduled to issue a final ruling on May 12,cited reservations expressed by the US Preventive Services Task Force,and expressed concerns about radiation exposure and the number of patients who would require follow-up colonoscopies to remove polyps,as well as the inability of CT scans to reliably detect small or flat growths.

The dispute has split doctors in the same specialty: the American Gastroenterological Association favours Medicare coverage,while the American College of Gastroenterology does not.

Through a peephole

One of the benefits of virtual colonoscopy is its ability to detect other cancers and abnormalities—tumours in the kidney,liver or lungs,and aortic aneurysms—because of its crisp images involving a wider area of the body. Klein describes: Optical colonoscopy involves peering through a peephole,while virtual colonoscopy means opening the door.

Proponents say CT scan technology also makes it easier for doctors to find polyps and cancers on the right side of the colon,which can be missed in optical colonoscopy for anatomical reasons.

“It is a double-edged sword,” said David Vining,a professor of diagnostic radiology at MD Anderson Cancer Centre in Houston,who invented virtual colonoscopy. Incidental findings can trigger a cascade of expensive,invasive,anxiety-provoking tests that in most cases will reveal something benign. But Vining said in about 5 per cent of patients,virtual colonoscopy could find a serious problem such as cancer “that can be easily treated and cured” and might otherwise be discovered at a much later stage,when treatment is more difficult and outcome less favourable. Unlike optical colonoscopy,in which all polyps are removed,many radiologists do not report most growths smaller than about five millimetres,believing they are usually harmless.

“Who knows whether those polyps turn into cancer,” said gastroenterologist G S Raju,adding that some researchers believed there was a subset of small polyps that were aggressive and malignant.

Rosemarie Blair of Newark believes virtual colonoscopy saved her life. After a friend died of colon cancer,the 60-year-old made an appointment for a virtual colonoscopy. She had never undergone the traditional test because she was “scared of being put to sleep”. The doctor found two polyps,which were removed a few hours later. Two days later,Blair’s internist called: The radiologist had spotted something suspicious on her kidney. An ultrasound revealed early-stage cancer. Blair,who had not experienced any symptoms,underwent a surgery to remove her right kidney. Doctors told her that because it was caught early,unlike most kidney cancers,she did not need chemotherapy or radiation,and her chances of a complete recovery were excellent.

But incidental findings are no reason to choose virtual colonoscopy,proponents emphasise. “You don’t get (it) to look at the rest of your body,” said Brooks Cash,chief of medicine at the National Naval Medical Center in Bethesda. For the past few years,patients at the hospital have been able to choose either form of colonoscopy and,if necessary,have both procedures the same day. So far,Cash said,more than 7,000 patients have undergone virtual colonoscopy — about 40 per cent of the total. “We don’t view it as a replacement or better than colonoscopy,but as another screening tool,” he said.

Exposure to radiation from virtual colonoscopy,supposed to be repeated every five years,remains a concern. Studies have found that multiple CT scans can increase the risk of cancer. Cash said he did not consider radiation exposure from virtual colonoscopy to be a problem. The amount from one test,he said,is “less than an airline pilot would get in one year of flying”. But John Petrini,a gastroenterologist who heads the American Society for Gastrointestinal Endoscopy,says one virtual test is equivalent in radiation dose to 250 chest X-rays. Virtual colonoscopy does not eliminate one of the most frequently cited impediments to screening: the dreaded prep. Patients undergoing both kinds of colonoscopy must drink a large quantity of vile-tasting,bowel-cleansing liquid before the test. And unless a practice offers same-day optical colonoscopy — and most don’t — patients who need a follow-up procedure to remove polyps must drink it twice.

Clean bill of health

At Washington Radiology Associates,one of the few local practices offering virtual colonoscopy,the demand for the procedure has increased in the past year.

One recent morning,Rowe,the first patient of the day,listened intently as Klein explained that a technician would first insert a small,flexible tube into his rectum so that carbon dioxide could be pumped in to inflate his colon,enhancing its visibility. This can cause some transitory cramping,he said,but few patients find it painful.

Rowe climbed onto the table and lay motionless on his back,then his stomach,as rapid-fire X-rays of his colon were shot,then assembled into three-dimensional images on the computer. Back in the darkened reading room,Klein immediately sees that a portion of Rowe’s colon did not distend sufficiently,which occurs in about 10 per cent of cases. Rowe gets back on the table for another go-round.

The radiologist then spends the next 20 minutes reading the scan. Klein “flies” through Rowe’s colon,which resembles an orange cave with low-hanging walls. He swoops in to inspect possible abnormalities: a potential polyp turns out to be just pooled fluid. “I’m 95 per cent sure he’s fine,” Klein says,zeroing in on six areas flagged by the specialised software.

The last check is of liver,lungs and spine: Klein notes some degeneration of Rowe’s spine indicative of arthritis. “There are no polyps,no tumours,and the rest of your body is fine as far as we can tell,” Klein tells him.

Later that day,Rowe said he felt “pretty good” — pleased with his ability to go to work after the test. “I’ll probably do another one in five years,” he said.