By Dennis Thompson
MONDAY, Sept. 12 (HealthDay News) -- Whether the most technologically advanced way to check for colon cancer will become the standard screening method of the future does not appear to be a slam-dunk.
The method, known as virtual colonoscopy, combines X-ray and computer technology to create three-dimensional views of the full length of the colon, the large intestine. It allows doctors to look for polyps, or pre-cancerous growths, or other signs of cancer or other intestinal disease. According to the U.S. National Cancer Institute, virtual colonoscopy can be done with computed tomography (called a CT or CAT scan) or with magnetic resonance imaging (MRI).
Colon cancer is one of the few types of preventable cancer, with doctors able to find and remove pre-cancerous polyps in the colon before cancer can develop. The current "gold standard" procedure for colon cancer screening, however, is colonoscopy, a time-consuming procedure for which preparation is unpleasant and sedation is necessary.
Perhaps because of this, only half of all people older than 50 have gotten this potentially life-saving test for colon cancer, according to the U.S. Centers for Disease Control and Prevention.
Doctors who tout the virtual form of colonoscopy argue that it takes less time and does not require sedation and is a more comfortable procedure for those having it.
Yet others contend that its drawbacks far outweigh its benefits.
"It's a test that has a tremendous number of questions still yet to be answered," said Dr. David A. Johnson, chief of gastroenterology at Eastern Virginia Medical School, past president of the American College of Gastroenterology and co-author of the group's guidelines for colon cancer screening.
Virtual colonoscopy, however, has advanced far enough that it's now recommended as a frontline screening test by the American Cancer Society and as an alternative to regular colonoscopy by the American College of Gastroenterology.
Some major health insurers, including United Healthcare, CIGNA and BlueCross BlueShield, have begun covering virtual colonoscopy, said Dr. Judy Yee, an associate professor and vice chairwoman of radiology and biomedical imaging at the University of California, San Francisco, and chief of radiology at the San Francisco VA Medical Center.
In fact, when President Obama underwent his first-ever colon cancer screening last year, he chose virtual colonoscopy, Yee said.
People who have a virtual colonoscopy still have to undergo the same preparation that they would for a normal colonoscopy, in which powerful laxatives are used to clear out the colon -- a process that many, if not most, describe as unpleasant at best.
But anesthesia is not needed for the procedure, which means they can be back to their regular routine immediately afterward.
"It's a less invasive test," Yee said. "You don't have to introduce a 6-foot-long probe into the colon through the rectum."
Virtual colonoscopy does have its drawbacks, however.
For one thing, tissue samples cannot be taken, nor can a polyp be removed, during a virtual colonoscopy. If doctors believe they've located a polyp, then the patient has to have a second procedure -- a normal colonoscopy -- to confirm the diagnosis and have the polyp removed. That could be done on the spot, thus requiring only one procedure, if the person were having a regular colonoscopy.
Also, virtual colonoscopy may be a less accurate test. It produces very clear images, but experts say they're not as detailed as what can be seen in a conventional procedure.
Studies have found that virtual colonoscopy is not a reliable tool for locating polyps less than 5 millimeters in size or smaller, which constitute about 80 percent of pre-cancerous polyps in the colon, according to the American College of Gastroenterology.
The test also produces a considerable number of false positives, suggesting a problem that turns out to not be there. But, determining that requires people to undergo a normal colonoscopy.
"They not only are not detecting a sizable number of polyps, they are calling polyps that aren't there," Johnson said.