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Should You Get a Virtual Colonoscopy?


New research shows that it may offer advantages over the conventional form of this test

Until recently, most doctors agreed that the “gold standard” for the screening of colorectal cancer was conventional colonoscopy. Also known as optical colonoscopy, this procedure allows the doctor to view the inside of a patient’s colon with a camera that is attached to the end of a long, flexible tube that is inserted into the rectum and colon.

Now: A large study recently reported in The New England Journal of Medicine found that computed tomographic (CT) colonography — also known as “virtual” colonoscopy — may be just as effective as a colorectal screening tool as conventional colonoscopy — without carrying a risk for colon perforation (damage to the intestinal wall).

What you need to know about your options for colonoscopy… *


Cancers arise from growths (polyps) over the course of 10 to 15 years. If every eligible adult had a colonoscopy to detect and remove these growths, the vast majority of cancers could be prevented. However, only about half of American adults who should be screened for colorectal cancer actually undergo any type of testing.

Why are so many people avoiding this potentially lifesaving form of cancer screening?


Any pain related to conventional colonoscopy is typically well-controlled by sedation, but the exam requires a 24-hour bowel preparation, including a liquid diet and medications that cause diarrhea to cleanse the colon. When receiving conventional colonoscopy, most patients spend about half a day at a hospital or clinic, and they must arrange transportation because they are not allowed to drive after being sedated.

CT colonography also requires a colon cleanse, but the test itself takes only about 15 to 20 minutes. No sedation is given, so people who drive can take themselves home.

For these reasons, many medical experts believe that more Americans will undergo screening for colorectal cancer when CT colonography becomes more widely available — about 17% of US hospitals currently offer CT colonography services. The American Cancer Society now includes CT colonography as one of its recommended tests for colorectal cancer screening.

Key issues that influence the effectiveness of colonoscopy — and how each method stacks up…

  • “Hidden” polyps. Conventional colonoscopy is very effective, but there are problem areas that the camera can’t see, including the back side of folds and the right side of the colon. Skilled doctors can often minimize these “blind spots” during conventional colonoscopy, but those areas appear to be easier to view with CT colonography.
  • Polyp size. The high-definition cameras and computer monitors that are often used in conventional colonoscopy allow the doctor to examine the intestinal lining in crisp detail.Small polyps (less than 5?16 inch) can be more difficult to see on a CT scan compared with conventional colonoscopy. Some experts argue that any missed growth is unacceptable — that conventional colonoscopy, at least for now, is superior because it’s more likely to detect small polyps and possibly flat lesions that can lead to colon cancer.It’s important to note, however, that fewer than three in 10,000 growths smaller than 3?16 inch are cancerous. Moreover, the few tiny polyps that could develop into cancer in the future could be removed at a later screening, when they have grown larger and before they change to cancer.
  • Incidental findings. Conventional colonoscopy visualizes only the intestinal wall. Since a CT scan has a field of view that encompasses tissues and organs beyond the intestine, 7.4% to 11.4% of people who undergo CT colonography are found to have abnormalities, including life-threatening conditions, such as an aortic aneurysm (an abnormal swelling in the wall of the body’s main artery), that might have gone undetected without the test.However, incidental findings can lead to batteries of expensive tests to investigate abnormalities that usually turn out to be harmless. About 2% of screened people have findings beyond the colon that turn out to be significant and require treatment.
  • Repeat testing. Since CT colonography only visualizes, people who have growths that need to be biopsied or removed will require a subsequent conventional colonoscopy.My advice: People with normal colon cancer risk factors are good candidates for CT colonography. Among average-risk people, about 10% will need conventional colonoscopy as well. If you’re at known high risk for polyps and/or cancer (due to a personal history of an inflammatory bowel disease, for example), it’s usually better to have a conventional colonoscopy.Before scheduling a CT test: Ask the doctor whether a subsequent colonoscopy, if needed, can be performed the same day. This saves you from having to repeat the bowel-prep procedure.
  • Risks. With conventional colonoscopy, perforation — which typically leads to surgical removal of part of the injured colon and can, in rare cases, cause death — occurs in about one in 1,000 procedures. CT colonography doesn’t require the insertion of a lengthy optical tube, although a small tube is inserted a few inches into the rectum to inflate the colon with carbon dioxide gas so that the intestinal wall can be easily viewed. There’s virtually no risk for perforation during the CT procedure.New finding: With conventional colonoscopy, research shows that the complication risk (including perforation) rises with age in adults age 65 and older.
  • Radiation. If you’re concerned about radiation exposure, you may choose to avoid CT colonography. Depending on the imaging machine, patients are exposed to 50 to 100 times the radiation that they would get from a single chest X-ray.To put this into perspective, someone who lives in Denver is exposed to about the same amount of radiation each year — from cosmic rays and radon — as is used in two CT colonographies.
  • Cost and insurance. Medicare currently does not cover CT colonography (cost: about $400 to $800) as a mass screening procedure, but that may change considering new data that now supports the use of this technology in older adults. Conventional colonoscopy (cost: about $1,500) is covered by most insurance plans. While conventional colonoscopy is usually repeated every 10 years, CT colonography is typically performed every five years.

    *Men and women at average risk of developing colorectal cancer should start screening for colorectal cancer at age 50, or earlier if they have a personal history of colorectal cancer or polyps, a history of chronic inflammatory bowel disease, a strong family history of colorectal cancer or polyps, or a known family history of hereditary colorectal cancer syndromes.

Source: David H. Kim, MD, associate professor of radiology and the residency program director at the University of Wisconsin School of Medicine and Public Health in Madison. He is a researcher in computed tomographic colonography and the lead author of multiple studies, including recent analyses published in The New England Journal of Medicine and the February 2010 issue of Radiology. Date: April 1, 2010 Publication: Bottom Line Health
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