Colorectal Cancer Chapter 9
A Less Invasive Look
Virtual colonoscopy is a new technology that uses computed tomography (CT), or, less often, magnetic resonance imaging (MRI) images to look for polyps, cancer, or other diseases of the colon when an abnormality is suspected. A computer program assembles the images to create an animated, three-dimensional view of the interior of the colon. The preparation for the procedure is similar to that for a colonoscopy, but the procedure itself takes only about 10 minutes, and no sedation is required. If abnormalities are found, a conventional colonoscopy will need to be performed for removal or biopsy of the growth.
The CT procedure takes place as follows:
- The patient lies face up on a table.
- A thin tube is inserted through the anus and into the rectum. Carbon dioxide gas is pumped through the tube to expand the large intestine for better viewing.
- The table moves through the CT scanner to produce a series of cross-sectional images of the colon.
- At certain times during the procedure, the doctor may ask the patient to hold his or her breath so that the image will be clear.
- The procedure is repeated while the patient lies face down.
After the image-taking procedure is complete, the cross-sectional pictures are processed by the computer to create animated, three-dimensional images of the large intestine. They are examined by a radiologist to identify any abnormal growths. If abnormalities are found, then a conventional colonoscopy will need to be performed so that the abnormal growths can be removed or biopsied.
Advantages of virtual colonoscopy:
- Virtual colonoscopy is less invasive than conventional colonoscopy and does not require the insertion of a colonoscope into the entire length of the colon.
- Virtual colonoscopy takes less time than either conventional colonoscopy or a barium enema. It takes only about 10 minutes to do the exam, and about 15-30 minutes more to read the results.
- No sedation is needed. The person having the procedure can return to usual activities or go home afterwards.
- Virtual colonoscopy provides clearer, more detailed images than a barium enema.
- Virtual colonoscopy can provide images of a colon that is narrowed due to inflammation or the presence of an abnormal growth.
- Virtual colonoscopy can discover clinically important problems outside of the colon, such as other cancers and aortic aneurysms. The scan provides data about the entire abdomen and pelvis and the solid organs they contain, including the liver, kidneys, pancreas, and bladder. In men, the prostate can be checked, and in women, the uterus and ovaries.
Disadvantages of virtual colonoscopy:
- Like conventional colonoscopy, virtual colonoscopy requires bowel preparation.
- The exam is slightly invasive in that a small tube is inserted into the rectum to expand the large intestine.
- Virtual colonoscopy does not allow the doctor to remove or biopsy tissue. If something suspicious does turn up during a virtual colonoscopy, then a traditional colonoscopy must be done. The patient must go through another bowel-preparation regimen and another procedure.
- Because the virtual colonoscopy provides data about the entire abdomen and pelvis and the solid organs they contain, it may reveal the presence of cysts and other growths. Although these growths may turn out to be harmless, they can lead to further testing, increasing both cost and risk to the patient.
- Virtual colonoscopy does not detect precancerous polyps smaller than .4 inches (10 mm).
- Medicare and many health insurance plans don't pay for virtual colonoscopy.
- Virtual colonoscopies expose the patient to low doses of X-ray radiation.
- Virtual colonoscopy is a newer technology and not as widely available as conventional colonoscopy, although this may change.
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