A virtual colonoscopy is used to identify abnormalities in your colon and rectum, which are both part of your large intestine. In this procedure, pictures of the inside of your large intestine are taken from outside your body.
A CT scan is used to construct the images of your large intestine. After the scan, a computer combines the images of your large intestine to produce 2-D and 3-D interior views. A virtual colonoscopy is sometimes referred to as a CT colonography.
In some cases, an MRI is used instead of a CT scan.
A virtual colonoscopy and a conventional colonoscopy use different tools to retrieve the images of your colon.
A conventional colonoscopy uses a colonoscope. A colonoscope is a long, lighted tube with a small camera at the end. It’s placed inside your colon and rectum, and the camera sends images of the area to a video monitor.
A virtual colonoscopy allows your doctor to look at your colon and rectum to find abnormal areas. Abnormalities that may be detected and diagnosed include:
- diverticulosis, which causes small pouches in your digestive tract
- internal bleeding
- polyps, which are growths of tissue in your colon and rectum
- tumors in your abdomen or the areas surrounding your kidney, liver, pancreas, or spleen (these organs lie near your large intestine)
- colorectal cancer
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.
The British Medicine Journal (BMJ) and the American College of Physicians (ACP) both recommend that people at average risk of colorectal cancer start screening when they’re at least 50 years old and stop screening when in their 70s.
The American Cancer Society (ACS) recommends that people at average risk start screening when they’re at least 45 years old and stop screening when they’re in their 70s or 80s.
The BMJ guidelines state that having a colonoscopy just once is sufficient for people at average risk. However, they don’t specifically mention the virtual colonoscopy.
On the other hand, the ACP and ACS recommend that people receiving virtual colonoscopies are screened every 5 years.
When to screen more often
If you have a higher risk of colorectal cancer, your doctor will set up a screening schedule for you.
High-risk factors include having:
- a prior history of polyps or colorectal cancer
- inflammatory bowel disease (IBD)
- a family history of polyps or colorectal cancer
You may begin regular screenings before you reach ages 45–50.
The virtual colonoscopy is a relatively new screening tool, so more evidence is needed to judge the harms and benefits.
However, there appear to be few risks associated with a 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.
There’s a very small risk that inflating your colon could cause injury. The ACS considers this risk to be much lower with a virtual colonoscopy than a conventional colonoscopy.
Reaction to the contrast agent
In rare instances, some people have a negative reaction to the contrast agent that’s used to highlight your large intestine.
Though uncommon, mild reactions can include:
Moderate to severe responses to the contrast agent, though rare as well, resemble an allergic reaction:
- hives or itching
- difficulty breathing or swallowing
- distress or confusion
- rapid heartbeat
- a bluish skin color
Reaction to radiation
Like other types of CT scans, a virtual colonoscopy subjects you to a small amount of radiation. Side effects of radiation exposure include fatigue, hair loss, and changes to the skin (such as blistering).
To help your doctor get the clearest images, your colon and rectum must be emptied before a virtual colonoscopy. This is called bowel preparation (bowel prep).
To do this, you’ll have to:
- Follow a clear liquid diet for 1 to 3 days before the exam.
- Avoid eating or drinking 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 1 week before the exam. This allows time for your doctor to make any necessary changes to your medication schedule.
A virtual colonoscopy is an outpatient procedure, but it’s usually performed in a hospital.
You won’t be checked into the hospital and can leave the same day as the test. You won’t be sedated either.
The test takes about 10 to 15 minutes to complete. The testing process is as follows:
- If you’re 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 allow for closer examination.
- For MRI exams, a contrast agent that’s given rectally is used to enlarge the area.
- The table you’re 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’ll have at least 2 scans, each lasting about 15 seconds.
- After the exam, you’ll be able to release the gas in the restroom.
- You can return to work or normal activities after the exam.
A virtual colonoscopy has some distinct advantages over a conventional colonoscopy, such as:
- A virtual colonoscopy takes about 10 to 15 minutes, while a conventional colonoscopy takes about 15 to 60 minutes.
- A virtual colonoscopy may be more comfortable for some people, since it doesn’t use a colonoscope.
- You don’t need a sedative during a virtual colonoscopy, whereas a conventional colonoscopy usually requires one.
- You can resume normal activities after a virtual colonoscopy, but people usually need time to recover from the sedatives used in a conventional colonoscopy.
- A virtual colonoscopy has less risk of colon tearing, or perforation, than a conventional colonoscopy.
There are a few disadvantages of a virtual colonoscopy:
- A virtual colonoscopy isn’t as sensitive as a conventional colonoscopy for finding smaller polyps.
- Your doctor can’t remove a tissue sample or polyp using a virtual colonoscopy. If a tissue sample is needed, you’ll need to have a conventional colonoscopy.
- 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 isn’t satisfied with the images, you may need to repeat the procedure 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 test results are positive. During this procedure, abnormal tissue samples can be obtained and polyps can be removed.
Virtual and conventional colonoscopies both have their pros and cons. Be sure to talk to your doctor about any questions you may have and about which procedure they recommend.