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Tests & Procedures : Gastroenterology

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Virtual Colonoscopy for Cancer Screening

Virtual colonoscopy is a procedure that is done to look for small polyps or other growths inside your colon. Polyps that grow on the inside lining of the colon sometimes turn into colon cancers. The American Cancer Society recommends that men and women start being screened for colon cancer at age 50. If you have a family history of colon cancer or are at high risk for other reasons, your doctor may want you to begin screening even earlier.

Procedure overview

Virtual colonoscopy is done by taking hundreds of cross-sectional X-rays of the colon using a powerful type of computer. The computer can put all the images together to form the whole picture. These images can then be viewed by X-ray specialists and your doctors. This type of imaging is called computed tomography (CT), and the machine that makes them is called a CT scanner. The images can also be copied, transferred, and printed.

Reasons for the procedure

Colon cancer is the fourth most common cancer in men and women. The reason for virtual colonoscopy is to find colon cancer at an early stage when it can be treated most successfully.  Colon polyps that are found by virtual colonoscopy can be removed (in a different procedure) before they turn into cancer.

An older and still common type of colonoscopy, called conventional colonoscopy, is also done to screen for colon cancer. This procedure is done by placing a long, flexible, lighted scope and tiny camera into the colon so that the doctor can look at the colon directly.

Virtual colonoscopy has several advantages over conventional colonoscopy:

  • Virtual colonoscopy is less uncomfortable and invasive than conventional colonoscopy and usually does not require any pain medication or anesthesia.

  • Virtual colonoscopy takes less time and poses less risk of puncturing the large intestine.

  • Virtual colonoscopy may be used in people who have problems such as swelling, bleeding, or breathing difficulties and who may not be able to tolerate conventional colonoscopy.

  • Virtual colonoscopy may be able to get to areas of the large intestine that conventional colonoscopy can't reach.

Risks of the procedure

Virtual colonoscopy is a safe procedure, but it's not without risk. Conventional colonoscopy, however, also has some drawbacks. Among the risks and disadvantages of virtual colonoscopy:

  • During virtual colonoscopy, a small, short tube is placed into your anus so that air can be pumped into your colon. This inflates your colon so that polyps or other growths are more easily seen. Pumping air into the colon carries a very small risk that it may cause a rupture. This risk is less than one in 10,000.

  • Because polyps or suspicious growths cannot be removed or biopsied during virtual colonoscopy, you may still need to have a conventional colonoscopy if your doctor feels that any images on virtual colonoscopy need further investigation.

  • Virtual colonoscopy cannot identify polyps that may turn into cancer if they are smaller than 10 mm.

  • Radiation received during virtual colonoscopy is small, but it could be dangerous for pregnant women. If you are or could be pregnant, you should discuss this risk with your doctor before the procedure.

  • Virtual colonoscopy is less expensive than conventional colonoscopy, but it is not always covered by medical insurance.

There may be other risks, depending on your specific medical condition. Be sure to discuss any concerns with your doctor before the procedure.

Before the procedure

Before having a virtual (or a conventional) colonoscopy, you will need to have a bowel prep. A bowel prep is a way of emptying everything solid from your colon so that the CT images will be clear. Here is what is often involved with a bowel prep:

  • Your doctor may ask you to limit your diet to clear liquids such as water, Gatorade, or clear broth for a day or two before the procedure.

  • The day before the procedure, you will be given a laxative in pill form or powder dissolved in liquid to help you empty your colon.

  • Just before the procedure you may be given a type of liquid to drink called contrast media that helps the inside of your colon appear brighter for the X-rays.

Always tell your doctor about any medications you are taking and if you've had any reactions to contrast media for other X-rays in the past.

During the procedure

Virtual colonoscopy can be done wherever a CT scanner is available. In most cases you will go to the radiology department of a hospital or medical center. The actual procedure takes only about 10 to 15 minutes. This is what usually happens during a virtual colonoscopy:

  • The thin tube will be placed into your rectum to inflate your colon with air. You may feel a slight fullness.

  • A radiologist will position you face up on a table that slides into the CT scanner.

  • The radiologist will leave the room and the CT scanner will be operated from a separate control room. You will be able to hear and talk with the staff.

  • The table will move into and through the scanner. You may hear some whirring and clicking noises.

  • You may be asked to hold your breath at times.

  • The scan may need to be repeated while you lie face down.

After the procedure

In most cases you should be able to return home without assistance and resume your normal diet and activities. Medications and special instructions are usually not needed, but always check with your doctor and the radiology staff if you have any questions.