Virtual Colonoscopy for Colorectal 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 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 also called CT colonography. It 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 looked at by your healthcare providers. This type of imaging is called CT. 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. This lets the healthcare provider 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. It usually does not need any pain medicine or anesthesia.
Virtual colonoscopy takes less time. It also poses less risk of puncturing the large intestine.
In certain cases, virtual colonoscopy may be used in people who have problems such as swelling, bleeding, or breathing difficulties. It may also be done for some people who may not be able to have conventional colonoscopy.
Virtual colonoscopy may be able to show areas of the large intestine if conventional colonoscopy can't reach them for some reason. This might be 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. But conventional colonoscopy 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.
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 found.
Virtual colonoscopy can miss some polyps that may turn into cancer if they are smaller than 10 mm. Some of these might be seen 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. It may not always be covered by health insurance.
You may have other risks, depending on your health 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 for a day or two before the procedure. These might be water, clear broth, or an electrolyte solution.
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. This helps the inside of your colon show up brighter for the X-rays.
Always tell your healthcare provider about any medicines you are taking. Also tell your provider 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 put you face up on a table that slides into the CT scanner.
The radiologist will leave the room. 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 help and go back to your normal diet and activities. You usually will not need medicines or special instructions. But always check with your healthcare provider and the radiology staff if you have any questions.
March 22, 2017
Tests for screening for colorectal cancer: Stool tests, radiologic imaging and endoscopy, UpToDate
Alteri, Rick, MD,MMI board-certified, academically affiliated clinician