Virtual Colonoscopy for Colorectal Cancer Screening
Virtual colonoscopy (also known as CT colonography) 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 most men and women begin screening for colon cancer at age 50. If you have a family history of colon cancer or are at high risk for other reasons, your healthcare provider may want you to begin screening even earlier. Virtual colonoscopy every 5 years is one of several screening choices.
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 create 3-D images of your colon and rectum. These images can then be viewed by your healthcare providers. This type of imaging is called computed tomography (CT), and the machine that makes them is called a CT scanner.
Reasons for the procedure
Colon cancer is the third 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 (using conventional colonoscopy) before they turn into cancer.
Conventional colonoscopy is also done to screen for colon cancer. This procedure is done by placing a long, flexible, lighted scope and tiny camera through the rectum and into the colon so that the healthcare provider can look at the colon directly and remove any polyps that are present.
Virtual colonoscopy has several advantages over conventional colonoscopy:
Virtual colonoscopy is less uncomfortable and invasive than conventional colonoscopy and usually does not need any pain medicine or anesthesia.
Virtual colonoscopy takes less time and poses less risk of puncturing the large intestine.
In certain instances, virtual colonoscopy may be used in people who have problems such as swelling, bleeding, or breathing difficulties and for some people who may not be able to tolerate conventional colonoscopy.
Virtual colonoscopy may be able to show areas of the large intestine if conventional colonoscopy can't reach them for some reason (such as if part of the intestine is narrowed or blocked).
Risks of the procedure
Virtual colonoscopy is generally 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. But the risk is thought to be much less than with conventional colonoscopy.
Because polyps or suspicious growths cannot be removed or biopsied during virtual colonoscopy, you will still likely need to have a conventional colonoscopy if polyps or other suspicious areas are detected.
Virtual colonoscopy can miss some polyps that may turn into cancer if they are smaller than 10 mm. (Some of these might be detectable by conventional colonoscopy.)
Unlike most other screening tests, virtual colonoscopy uses X-rays to create pictures of the colon and rectum. 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 healthcare provider before the procedure.
Virtual colonoscopy is still fairly new, and it may not always be covered by medical insurance.
There may be other risks, depending on your specific medical condition. Be sure to discuss any concerns with your healthcare provider 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 healthcare provider 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 strong laxative in pill or liquid form to help you empty your colon. You will likely have several loose or liquid bowel movements in the following hours.
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 healthcare provider about any medicines 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. Medicines and special instructions are usually not needed, but always check with your healthcare provider and the radiology staff if you have any questions.