Dec 28, 2003 - 1:07 pm
For anyone seeking to avoid the unpleasantness and discomfort of a colonoscopy, here's good news: A computed tomography (CT) scan that provides a "virtual colonoscopy" of the large intestine is just as adept at detecting signs of cancer as is a viewing device moved through the colon, a new study finds.
A team led by researchers at the National Naval Medical Center in Bethesda, Md., used a CT scanner to generate three-dimensional images of the colon, an emerging technique that seems to be more accurate than typical two-dimensional CT scanning. The 3-D images consistently revealed polyps growing inside the colon. Such growths aren't necessarily cancerous, but some can develop into tumors.
The scientists performed CT scans on 1,233 people, average age 58, who were free of signs of cancer. Next, without knowing the CT results, other doctors conducted a colonoscopy on each volunteer. In this procedure, a physician inserts a flexible, camera-tipped tube into a sedated patient's colon via the rectum and withdraws it gradually while watching a video screen for polyps.
In this generally healthy group of volunteers, only two cancerous polyps showed up. CT scanning spotted both, but colonoscopy found only one. Of 48 worrisome polyps at least 1 centimeter in diameter, 45 turned up in the CT scans and 42 were detected by the colonoscopy. Between them, the tests turned up 554 polyps deemed to have malignant potential.
"The results were quite comparable," says study coauthor Pauline A. Mysliwiec, a gastroenterologist now at the University of California, Davis, Medical Center in Sacramento. The report appears in the Dec. 4 New England Journal of Medicine.
Patients spent an average of 14 minutes in the CT scanning room, where they received a sometimes-uncomfortable infusion of air into the colon. A colonoscopy took 32 minutes during which patients were sedated to a dreamlike state.
Colon cancer kills nearly 60,000 people annually in the United States, even though it is largely preventable through polyp detection and removal. The Centers for Disease Control and Prevention in Atlanta reported earlier this year that fewer than half of U.S. residents over age 50 have had a colonoscopy or a sigmoidoscopy, a similar but less-thorough exam.
A physician who detects polyps during a colonoscopy routinely removes them using equipment built into the scope. A CT scan revealing a large polyp triggers a colonoscopy for the growth's removal.
However, colonoscopy has drawbacks as a screening tool. It risks perforating the colon, and the sedated patient requires up to an hour of recovery time and a ride home, say Martina M. Morrin and J. Thomas LaMont of Harvard Medical School in Boston in an article accompanying the new study. If the new findings are replicated and doctors can agree on how big a CT-detected polyp needs to be to warrant immediate removal, then "virtual colonoscopy is ready for prime time," Morrin and LaMont say.
The price tag for such a CT scan is "still being worked out," says John H. Bond, a gastroenterologist at the University of Minnesota and the Veterans Affairs Medical Center in Minneapolis. Once medical authorities agree that a CT scan is as good as colonoscopy, he predicts that Medicare and insurance companies will pay for CT-probably within the next 2 years.
"A lot of people are going to opt for this procedure," Bond says.