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.
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
The American 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
- ulcerative colitis
United States Preventive Services Task Force Recommendations
The United 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 technology.
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.
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 exam.
- 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.
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 rectum.
- For CT procedures, room air or carbon dioxide is slowly pumped into the tube to inflate your rectum and to allow for closer examination.
- 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.
- 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.
- 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 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.