Same Scans Allows Doctors to Look for Polyps, Measure Bone Density
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"If you're trying to decide whether to have a colonoscopy or virtual colonoscopy, you may want to opt for the latter as it has the added benefit of allowing us to determine your bone mineral density at the same time," says Rizwan Aslam, MBChB, assistant clinical professor of radiology at the University of California San Francisco. Low bone mineral density can indicate osteoporosis.
Speaking at the annual meeting of the Radiological Society of North America (RSNA), he noted that colorectal cancer and osteoporosis generally affect adults over age 50.
Virtual colonoscopy, also known as CT colonography, begins with an abdominal CT scan, which creates cross-sectional images of all structures in the abdomen, including the spine. Computer software then arranges the CT images to create a "fly-through" view of the colon, allowing doctors to look for polyps that can lead to cancer as well as cancer itself.
Using the same CT images, another software application can create three-dimensional images of the spine, allowing bone mineral density to be measured.
Recent studies suggest that virtual colonoscopy is as accurate as the real thing, and this year, the American Cancer Society, the American College of Radiology, and the U.S. Multi-Society Task Force on Colorectal Cancer added CT colonography to the list of colon cancer screening options.
Still, only about 40% of people get the recommended colon cancer screenings, Aslam says. The added benefit of being able to screen for osteoporosis using virtual colonoscopy may help improve that statistic, he says.
"It's just a question of manipulating the same data for extra information," he says.
The Downside of Virtual Colonoscopy
A downside of virtual colonoscopy is that it requires the same bowel prep (cleansing of the bowels) as a real colonoscopy, says RSNA spokesman Philip O. Alderson, MD, dean of St. Louis University School of Medicine.
"Here is a chance to get an elegant look at bone mineral density without an extra procedure, and that's great. But what will really make patients want virtual colonoscopy is when we figure out how to do it without the rigorous prep," he tells WebMD.
The new study, conducted at the San Francisco Veterans Administration Hospital, involved 30 men and five women aged 54 to 79. Bone mineral density measurements obtained from the virtual colonoscopy scans were compared with those obtained using dual-energy x-ray absorptiometry (DEXA), the standard bone density screening tool.
"There was excellent correlation," Aslam says.
"CT colonography isn't a replacement for DEXA testing, but it could be a way to screen more people for osteoporosis using off-the-shelf software that any doctor can obtain," he says.
Aslam says that if a virtual colonoscopy scan shows a person has low bone density, "treatment can be started right away. Then, the next follow-up exam would be DEXA."
According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, 10 million Americans have osteoporosis. A out 34 million more are at risk because of low bone mass.
SOURCES: Radiological Society of North America 2008, Chicago, Nov. 30-Dec. 5, 2008. Rizwan Aslam, MBChB, assistant clinical professor of radiology, University of California San Francisco. Philip O. Alderson, MD, dean, St. Louis University School of Medicine. National Institute of Arthritis and Musculoskeletal and Skin Diseases: "Osteoporosis Overview."
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