Virtual Colonoscopy Still Has Its Skeptics09/12/11
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
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
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
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
"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
In fact, when President Obama underwent his first-ever colon
cancer screening last year, he chose virtual colonoscopy, Yee
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
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
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
"They not only are not detecting a sizable number of polyps, they are calling polyps that aren't there," Johnson said.
Then there's the question of exposure to radiation, which he
described as "not inconsequential."
Radiologists and advocates of virtual colonoscopy acknowledge
the concerns but argue that the test has proven its value.
For example, though virtual colonoscopy might not be as
accurate, it is effective in finding the polyps that most often
lead to colon cancer, Yee said.
"Virtual colonoscopy has been shown through multiple studies to be as sensitive as normal colonoscopy to detect clinically significant lesions of 10 millimeters or larger," she said.
Yee added that radiation concerns are overblown. "It's been
shown that virtual colonoscopy is a low-dose examination," she
Researchers also are working to make virtual colonoscopy even
better, Yee said. New computerized, post-processing techniques are
being developed to improve the test's accuracy and lower the
radiation dose, and doctors are working to develop a form of the
test for which the patient would not need to take laxatives in
At the moment, though, the American College of Gastroenterology
still would prefer that people have a conventional colonoscopy done
every 10 years because, as Johnson said, it's a better test that
allows doctors to immediately remove any polyps that are found.
However, if the drawbacks of a normal colonoscopy are enough to
dissuade a person from undergoing colon cancer screening, then they
should consider virtual colonoscopy as an alternative test that
they should have every five years, according to ACG guidelines.
The hope is that virtual colonoscopy "will bring in individuals
who aren't ever considering being screened, who need to be
screened," Yee said. "We'd like to bring patients in before the
cancer ever develops."
The U.S. National Digestive Diseases Information Clearinghouse
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