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Virtual Colonoscopy for Colorectal Cancer Screening

What is virtual colonoscopy?

Virtual colonoscopy is a test that's used to look for polyps or other growths inside your colon before they cause problems. (Looking for cancer before it causes symptoms is called cancer screening.)

Polyps that grow on the inside lining of the colon may turn into colon cancer over time. Finding and removing them can keep this from happening. Virtual colonoscopy every 5 years is one of many colon cancer screening choices.

The American Cancer Society and U.S. Preventive Services Task Force advise that people at average risk for colon cancer start screening for it at age 45. If you have a family history of colon cancer or are at high risk for other reasons, you may need to start screening earlier.

Virtual colonoscopy is also called CT colonography. CT stands for computed tomography. A CT scanner takes many X-rays of the colon. A computer puts all the X-rays together to create 3-D images of your colon and rectum. These images can show polyps or other changes inside your colon and/or rectum.

Why might I need a virtual colonoscopy?

Colon cancer is a common cancer. Virtual colonoscopy can be used to find colon cancer at an early stage–when it's small and can be easier to treat.

A regular colonoscopy is also used to screen for colon cancer. For this test, a long, flexible, lighted tube (called a scope) with a tiny camera on the end is put into the rectum and slid up into the colon. This lets the healthcare provider look right at the colon wall and remove any polyps that are found. Colon polyps that are found by virtual colonoscopy cannot be removed during the test. A regular colonoscopy must be done to take them out before they turn into cancer.

Virtual colonoscopy has some benefits over regular colonoscopy:

It's less uncomfortable and nothing is put into your body.
You don't need medicine (anesthesia) to get the test.
It's quick.
There's less risk of damaging the large intestine.
It may be able to show areas of the large intestine that regular colonoscopy can't reach. This may be the case if part of the bowel is very narrow or blocked.

Virtual colonoscopy might be used if you're not able to have regular colonoscopy. For instance, it may be a choice it you have problems with swelling or bleeding, or breathing problems.

What are the risks of virtual colonoscopy?

Every procedure has some risks and possible problems. For virtual colonoscopy, these include:

A small, short tube is put 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 tear (perforation). But the risk is thought to be far less than with regular colonoscopy.
Polyps or other growths can’t be removed with a virtual colonoscopy. You'll still need to have a regular colonoscopy if polyps or other growths are found.
This test can miss some polyps if they are smaller than 10 millimeters. Some of these might be seen by regular colonoscopy.
The test may show problems in other parts of your body (such as your kidneys, liver, ovaries, spleen, or pancreas) which can lead to more tests.
Unlike most other screening tests, the test uses X-rays to make pictures of the colon and rectum. The amount of radiation is small. But it may still raise your risk for cancer slightly. It could also be dangerous during pregnancy. If you are or could be pregnant, talk with your healthcare provider before the test.
Virtual colonoscopy may not be covered by your health insurance.

You may have other risks, depending on your health. Discuss any concerns with your healthcare provider before this test.

How do I get ready for a virtual colonoscopy?

Tell your healthcare provider about any medicines you take. This includes prescription and over-the-counter medicines, vitamins, herbs, or supplements you take. Also tell them about any implanted medical devices, such as a pacemaker.

Before having a colonoscopy, you'll need to do a bowel prep. This helps empty your colon so that the CT images will be clear. Here's how bowel prep is often done:

You may need to limit your diet to clear liquids for 1 or 2 days before the test. These might be water, clear broth, or an electrolyte solution. Follow any directions you are given for not eating or drinking.
The day before the test, you'll be given a strong laxative in pill or liquid form to help you empty your colon. Expect to have many loose or liquid bowel movements. You'll need to stay near a toilet.
Just before the procedure, you may be given a liquid to drink. This is a contrast dye. It helps coat any stool left inside your colon so it shows up more clearly on the X-rays. Tell your provider if you've had any reactions to contrast dye in the past.

What happens during a virtual colonoscopy?

Virtual colonoscopy can be done wherever a CT scanner is used. In most cases, it's done in the radiology department of a hospital or medical center. The scan takes only about 10 to 15 minutes. This is what happens during the test:

The thin tube will be put in your rectum. It's used to inflate your colon with air. You may feel a slight fullness.
You'll lie face up on a table that slides into the ring-shaped CT scanner.
The technologist will leave the room. The CT scanner is run from a separate control room. But you'll be able to hear and talk with the staff the whole time.
The table will slide into and through the scanner. You may hear some whirring and clicking noises.
You may be asked to hold your breath a few times.
The scan may be repeated while you lie face down or on your side.

What happens after a virtual colonoscopy?

In most cases, you should be able to return home without help. You can go back to your normal diet and activities. You may have gas and cramping right after the test as you move the air out of your colon.

No medicines or special instructions are needed. Talk with your healthcare provider and the radiology staff if you have any questions.