What Is a Virtual Colonoscopy?
A virtual colonoscopy is used to identify abnormalities in your
colon and rectum. These abnormalities include diverticulosis, bleeding, or signs
of colorectal cancer. The test is also used to locate polyps and growths of
tissue in your colon and rectum. These polyps and growths can be precancerous.
The procedure uses a CT scan to construct images of your
large intestine. After the scan, a computer combines the images of your colon
and rectum to produce two- and three-dimensional interior views. In some cases,
an MRI is used instead of a CT scan.
Virtual colonoscopy and conventional colonoscopy use
different tools to retrieve the images of your colon. Conventional colonoscopy
uses a colonoscope. This is a long, lighted tube that’s placed inside your
colon and rectum. It uses a small camera to send images of the area to a video
monitor. Virtual colonoscopy uses a CT scan or MRI to take pictures of the
inside of your colon from outside your body.
Diagnostic Uses of Virtual Colonoscopy
Virtual colonoscopy is used to diagnose diseases of the
colon, such as early detection of colon cancer in men and women. It allows your
doctor to look at your colon and rectum to find abnormal areas. These areas may
have polyps or tumors. If detected early, some polyps can be removed before
they turn into cancer. If cancer is already present, it’s more likely to be cured
if it’s found early.
American Cancer Society Recommendations
Cancer Society recommends starting regular colorectal screenings at age 50
in men and women who don’t have
a family history of colon cancer or other high-risk factors. They also advise screening every five
years for people who have had a virtual colonoscopy.
If you’re at a high risk for colon cancer, your doctor will
set up a screening schedule for you. High-risk factors include:
- family history of polyps or cancer
- Crohn’s disease
United States Preventive Services Task Force Recommendations
States Preventive Services Task Force (USPSTF) recommends screening for
colorectal cancer in adults aged 50-75, by using fecal occult blood testing,
sigmoidoscopy, or a colonoscopy. They also recommend against routine screening
for colorectal cancer in adults aged 76-85 years. The USPSTF does not include
either virtual colonoscopy or DNA stool tests as screening tests. They say there
is not enough current evidence to judge the harms and benefits of this new
Risks of a Virtual Colonoscopy
There are few risks associated with virtual colonoscopy. The
air released into your colon may make you feel bloated. But the feeling should
dissipate once you pass the air from your body. Rarely, some patients have a
negative reaction to the contrast agent, which highlights your large intestine.
Though uncommon, mild reactions can include:
- stomach cramps
Moderate to severe responses to the contrast agent, though
rare, resemble an allergic reaction. These responses may include:
- hives or itching
- difficulty breathing or swallowing
- distress or confusion
- rapid heartbeat
- bluish skin color
There’s a very small risk that inflating your colon could
cause injury. The American
Cancer Society considers this risk to be much lower with virtual colonoscopy
than conventional colonoscopy. Also, like other types of CT scans, this test
subjects you to a small amount of radiation.
Preparation for Virtual Colonoscopy
To help your doctor to get the clearest images, your colon
and rectum must be emptied before a virtual colonoscopy. This is called bowel
prep. To do this, you will have to:
- Follow a clear liquid diet for a day or two
before the exam.
- Not eat or drink anything the night before the
- Take a strong laxative, and possibly a suppository,
to help clear your bowels.
- Take a contrast agent in pill form at home.
Tell your doctor about any medications you’re taking at
least one week before the exam. This allows time for your doctor to make changes
to your medication schedule.
The Test: Procedure for Virtual Colonoscopy
A virtual colonoscopy is usually done in a hospital, but it
is an outpatient procedure. You will not be checked into the hospital and can
leave later on the day of the test. The test takes 10 to 15 minutes to complete
and you will not be sedated. The testing process is as follows:
- If you are having a CT virtual colonoscopy, you
may be asked to drink a liquid contrast agent. In some cases, you may take the
contrast in pill form at home.
- A thin, flexible tube will be placed into your
- For CT procedures, room air or carbon dioxide is
slowly pumped into the tube to inflate your rectum and to allow for closer
- For MRI exams, a contrast agent that’s given rectally
is used to enlarge the area.
- The table you are lying on will slide into the
CT or MRI machine. Your doctor may ask you to hold your breath for a few
moments in order to get a steady image.
- You will have at least two scans, each lasting
about 15 seconds.
- After the exam, you will be able to release the
gas in the bathroom.
- You can return to work or normal activities
after the exam.
Advantages of Virtual Colonoscopy vs. Conventional Colonoscopy
- Virtual colonoscopy does not use a colonoscope,
so it may be more comfortable for some people.
- People don’t need a sedative during virtual
colonoscopy, whereas conventional colonoscopy usually requires one.
- People can resume normal activities after a
virtual colonoscopy, but people usually need time to recover from the sedatives
used in a conventional colonoscopy.
- Virtual colonoscopy lasts about 10 to 15 minutes,
versus about 30 to 60 minutes for conventional colonoscopy.
- Virtual colonoscopy allows your doctor to
examine your colon to see if it’s constricted by swelling or abnormal growth.
- Virtual colonoscopy has less risk of colon
tearing, or perforation, than conventional colonoscopy.
Disadvantages of Virtual Colonoscopy vs. Conventional Colonoscopy
- In virtual colonoscopy, gas is released into your
rectum through a tube, but gas is not used during a conventional colonoscopy.
- If a tissue sample is needed, you will need to
have a conventional colonoscopy, as your doctor can’t remove a tissue sample or
polyp using a virtual colonoscopy.
- Virtual colonoscopy is not as sensitive as
conventional colonoscopy for finding polyps less than 10 millimeters in size.
- Some health insurance plans may not cover a
Understanding the Results of a Virtual Colonoscopy
After your virtual colonoscopy, a radiologist will review your
CT scan or MRI images. If your doctor is not satisfied with the images, you may
need to repeat the scan or have another type of screening.
If there are no abnormalities in your colon, the virtual
colonoscopy is negative. If there are any abnormalities or polyps, the test is
positive. Your doctor may recommend a conventional colonoscopy if your results
are positive. During this procedure, abnormal tissue samples can be obtained
and polyps can be removed.
Other abdominal problems unrelated to colorectal cancer may
also be found during virtual colonoscopy. Tumors in your abdomen or the areas
surrounding your kidney, liver, pancreas, or spleen may be detected. These organs
lie near your large intestine.
Both virtual and conventional colonoscopies have their pros
and cons. It’s important that you’re aware of the differences between the two.
Be sure to talk to your doctor about any questions you may have and about which
procedure they recommend.