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Virtual vs Regular Colonoscopy Argued Again
Nov. 26, 2004 The controversy over virtual
colonoscopy vs standard colonoscopy was heated up this month by news
releases from two medical groups. The radiologists praised a new study
of the effectiveness of virtual, which was answered by a news release
from the radiologists,
saying standard colonoscopy is still the most accurate.
The news from the American Roentgen Ray Society
issued November 1 was headlined, New Study Lays to Rest Concerns about
Virtual Colonoscopy
The respone from the Amercan Society for
Gastrointestinal Endoscopy was headlined, Virtual Colonoscopy Raises
Issues for Further Study.
Colorectal cancer (CRC) is the third most commonly
diagnosed cancer in men and women and the second leading cause of
cancer-related deaths in the United States and Western Europe. The
lifetime risk of developing CRC is approximately 6% of the adult U.S.
population and almost half will die as a consequence of CRC.
Senior citizens, the most frequent users of
colonoscopy, should consult their personal physician for what a
recommended colonoscopy method, but here are the arguments raging today.
What the radiologists say:
Virtual colonoscopy can effectively detect flat
lesions in the colon, a study of more than 1,200 patients shows. The
study results lay to rest concerns that virtual colonoscopy should not
be used as a screening tool to detect colon cancer because it cant
detect these lesions, the study authors say.
Studies from Asia have indicated that flat lesions
are quite common, and often turn into cancer, said Perry Pickhardt, MD,
associate professor of radiology at the University of Wisconsin Medical
School in Madison. Therefore it has been argued that virtual
colonoscopy should not be used as a screening tool if it misses these
lesions, he said.
However this study found that virtual colonoscopy
detected 80% of the flat lesions (47 of 59 lesions) that were 6mm or
more in size. Virtual colonoscopy detected 81% of the non-flat lesions,
Dr. Pickhardt said. Twenty-nine of the 59 flat lesions were adenomas,
which are potential precursors to cancer, said Dr. Pickhardt. Virtual
colonoscopy detected 83% of the flat adenomas. It detected 86% (156 of
181) non-flat adenomas, he added. It is apparent that virtual
colonoscopy is equally good for detecting both flat and non-flat types
of lesions, he said.
The study also found that flat adenomas are
uncommon in a typical western screening population, and advanced flat
neoplasms are rare, said Dr. Pickhardt. The study found no diminutive
flat lesions that were histologically advanced in the 1,233 patients
screened with virtual colonoscopy, he said.
The study was sponsored by the Department of
Defense and was conducted at the National Naval Medical Center in
Bethesda, MD, Walter Reed Army Medical Center in Washington, DC, and the
Naval Medical Center in San Diego, CA. All patients underwent both a
virtual colonoscopy and a standard (optical) colonoscopy. All were
considered healthy at the time of the colonoscopy examinations.
The study was published in the November 2004 issue
of the American Journal of Roentgenology.
What the radiologists say:
The American Society for Gastrointestinal Endoscopy
(ASGE) has reacted with caution to claims of the benefits of computed
tomography (CT) colonography, also referred to as virtual colonoscopy,
compared to standard colonoscopy.
"Standard colonoscopy is still the most accurate
test for detection and removal of cancer and pre-cancerous growths
(polyps) in the colon," stated David Lieberman, MD, Oregon Health
Sciences University, Portland VA Medical Center, Portland, OR. Dr.
Lieberman is a past ASGE President and a noted expert in the area of
colon cancer screening.
"Like any medical test, colonoscopy is not perfect,
and some polyps may be present, but not detected," Dr. Lieberman
explained. "However, most pre- cancerous polyps and virtually all
cancers will be detected, and can usually be removed during the
examination."
Virtual colonoscopy refers to the use of
radiological (x-ray) techniques, including computed tomography (CT) and
magnetic resonance imaging (MRI) scanning with computers, to produce
pictures or images of the colon. It is "virtual" because the images are
produced using radiation and evaluated on a computer screen, while a
standard colonoscopy uses a thin, flexible lighted viewing tube (a
colonoscope) that is threaded slowly through the colon to examine the
lining for polyps.
Both standard and virtual colonoscopy requires a
bowel preparation to cleanse the colon. Sedation is routinely used to
reduce or eliminate discomfort associated with standard colonoscopy, but
patients are not sedated for virtual colonoscopy.
Unlike standard colonoscopy, virtual colonoscopy
only provides images of the colon, but does not allow for immediate
biopsy or polyp removal at the time of the exam. Some abnormalities
detected during virtual colonoscopy will require a standard colonoscopy
for confirmation and management.
"The position of the ASGE Technology Assessment
Committee is that CT colonography is a rapidly evolving technology with
still rather varied results from the most recently published studies,"
said Bret T. Petersen, MD. Chair of the Technology Assessment Committee
and director of endoscopy at the Mayo Clinic in Rochester, Minn. "A
single recent study yielded very positive results, while most studies
suggest CT colonography still has significant room for development and
improvement before it becomes a primary screening tool for colorectal
cancer."
Issues concerning
virtual colonoscopy include:
-- Some studies show
that more than half of large polyps are not detected
by using virtual
colonoscopy. More research is needed to determine the
accuracy of the
test.
-- Currently, bowel
prep is required to clean the colon. If the test
reveals a polyp, a
colonoscopy is usually recommended. In most cases,
a patient may need
to have one prep for the CT colonography and then a
second prep for the
standard colonoscopy.
-- The safety of
repeating CT colonography at frequent intervals has not
been studied yet.
It is not clear if radiation exposure from multiple
exams would be
safe.
"Early detection of cancer and, more importantly,
the identification and removal of polyps that ultimately could become
cancers can decrease the mortality for this disease," stated ASGE
President David J. Bjorkman, MD, MSPH, SM (Epid), Dean of the University
of Utah School of Medicine.
Dr. Bjorkman said, "More than one in twenty adults
will develop colorectal cancer in their lifetime. Many of these cancers
can be prevented or cured with screening, such as a colonoscopy.
Colonoscopy is safe and accurate when performed by a fully-trained
endoscopist."
For more information, contact the ASGE at
http://www.askasge.org/ or call 1-866-305-ASGE.
Source: American Society for Gastrointestinal
Endoscopy
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