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Colorectal Cancer
and Screening

New Screening Technique:
"Virtual Colonoscopy" - Does It Work?

The American Cancer Society does not recommend virtual colonoscopy for early detection of colorectal cancer.

Virtual Colonoscopy (CTC): We’ve recently been bombarded with commercials for the new computed tomographic colonography (CTC), also called “virtual colonoscopy.”

CTC uses the same technology as CAT scans (Computer Assisted Tomography) to produce three-dimensional images of the inside of the colon.

Advertising misleadingly suggests that CTC is less invasive than colonoscopy because images are taken from outside the body. But from the patient’s point of view, this test is similar to a barium enema. The same full bowel cleansing is required for both. During the procedure, a tube is used to pump air into the rectum, blowing up the colon like a balloon to allow scanning. Considerable cramping is experienced without any relief from sedation.

Some radiologists assert that CTC is as effective as colonoscopy in detecting colon polyps. But, studies have found it to be significantly inferior. Many false positives require a colonoscopy, and many false negatives potentially miss a polyp that could be or could become cancer, especially if the scan is not done in an expert center with 3-D scanners, rather than the usually available 2-D scanners.

Another drawback of CTC concerns the removal of polyps. Gastroenterologists finding a polyp during a colonoscopy can remove it during the same procedure. But if polyps are found during CTC, you must undergo a colonoscopy anyway. Thirty to 60% of patients having a CTC must also have a colonoscopy.

CTC is simply not as effective as colonoscopy. These are the drawbacks that prevent it from being a recommended screening tool:

Drawbacks of Virtual Colonoscopy (CTC)

  • Diagnostic only: Virtual colonoscopy (CTC) cannot remove polyps or even biopsy anything suspicious.
  • Uncomfortable: CTC will inevitably be uncomfortable as compared to colonoscopy, which is rarely uncomfortable in the right hands, and is usually done with sedation anyway.
  • False-positives: False-positive results are common. Stool that has not been completely cleansed from the colon prior to the test can stick to the colon wall and look just like polyps or cancers. So many patients will require a colonoscopy anyway, even when they have no polyp at all.
  • False-negatives: On the other hand, studies show CTC and barium enema are equally poor at finding polyps or cancers bigger than 1cm; only 40% as compared to 98% for colonoscopy. That means CTC misses about 60% of even these larger polyps. So patients who really need a colonoscopy may not be advised to get one.
  • Unreimbursed: For these reasons, CTC is not reimbursed by Medicare or most insurance companies.

“GASTROCare® supports the American Cancer Society in not currently endorsing CTC for colorectal cancer screening,” said Dr. Harry Snady, “Until scientific studies show improved efficacy of CTC for preventing cancer, GASTROCare® continues to recommend colonoscopy - the “gold standard” for colorectal cancer screening.”

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