Q&A: Focus on Virtual Colonoscopy

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It's a simple fact that bears repeating this Colorectal Cancer Awareness Month: Colorectal cancer screening saves lives. If found early, these diseases, which include colon, rectal and anal cancer, often can be treated successfully.

While traditional colonoscopy has been the method of choice for decades, virtual colonoscopy (VC), also called CT colonography, is a relatively new alternative that offers a less-invasive option for some people.

vining.jpgDavid Vining, M.D., professor in the Department of Diagnostic Radiology at MD Anderson, who invented the procedure in 1993, answers questions about virtual colonoscopy.

What exactly is VC? How is it performed?

In virtual colonoscopy, a CT (computed tomography) scanner is used to examine the abdomen and pelvis. Then the images are analyzed with sophisticated two- and three-dimensional viewing techniques.

We can literally fly inside the computer-generated model of a patient's colon, looking for polyps (growths on the wall of the colon) that are the precursors to cancer.

The process has four steps:

  • Cleansing the bowel with laxatives the day before the procedure
  •  Inserting a small tube into the rectum to inflate the colon with carbon dioxide gas; room air may also be used, but it makes the procedure less comfortable
  • CT scanning of the abdomen and pelvis, which takes less than 10 seconds
  • Image analysis using specialized computers

What are some of the advantages of VC compared to traditional colonoscopy?

No sedation is required for VC, and that is a huge advantage. Another plus is that we can look beyond lesions that might be obstructing the colon or examine a tortuous colon (a longer than normal colon that may become twisted or coiled).

Since VC is less invasive, the risk of bleeding and tearing of the colon is significantly less.

What are some of the disadvantages and criticisms of VC?

The main disadvantage is that, while VC screens for precancerous polyps and cancers, they cannot be removed during the exam. So a follow-up colonoscopy might be required. Some physicians discourage VC on those grounds, saying, "If you get a VC and a polyp is found, you will have to have a colonoscopy. So why not have a colonoscopy in the first place?"

That is partly true, but only 20% of people have significant lesions that warrant biopsy or removal. So, if we screen everyone with colonoscopy, 80% will undergo colonoscopy -- with its inherent risks of bowel perforation and the need for anesthesia -- unnecessarily.

Since the CT scan covers all the organs in the abdomen and pelvis, VC often can detect disease outside the colon. Significant lesions of this type are found in about 10% of cases. This can be a blessing and a curse due to the potential for unnecessary workups of benign lesions. Rather than discarding VC, I think we need better practice management guidelines on what to do with these findings outside the colon.

Another criticism has been that the process gives the patient a low dose of radiation. However, most VCs use ultra-low dose techniques with an extremely small radiation risk.

Who might be a candidate for virtual colonoscopy?

I think average-risk asymptomatic adults age 50 and older should consider VC. It's a good idea to discuss the alternatives with your doctor.

How common is the technology?

Even though VC is endorsed by the American Cancer Society and other national groups, its adoption has been slow for several reasons including:
  • limited insurance coverage,
  • few well-trained providers and 
  • the public's general reluctance to comply with colon cancer screening recommendations
However, as insurance coverage increases, availability should follow.

The best VC exams generally are performed at large academic medical centers. It's a matter of the volume of cases a facility performs and the radiologist's experience in performing and interpreting VC examinations. The technology is available at most medical centers, but the devil is in the details in how to conduct the examinations.

What should people look for in choosing a facility?

Ask how many cases the facility has performed and the radiologist has interpreted. The American College of Radiology and the American Gastroenterological Association recommend that physicians who interpret VC exams have done at least 75, but I suggest that the more the better.

What types of research is MD Anderson doing?

Since bowel preparation is the largest barrier to most people seeking colon cancer screening, my research involves the development of new bowel cleansing approaches. These include solutions to dissolve feces and remove it from below without the need to drink the usual cleansing agents.

MD Anderson resources:

MD Anderson Colorectal Screening Guidelines

Additional resources:
American Cancer Society
American College of Radiology
American College of Gastroenterology


We had a number of good responses to this post on our Facebook page ( to this post, including one from the author, David Vining, M.D.

Betty G.
I've never had one done..they creep me out..

Sharon C. Waddell I want to learn more about this new procedure. I need one desperately . But can't deal w/prep. I Pray it's not too late . I've having serious problems for quite awhile.

Sharon C. Waddell
What does less-invasive mean ,please ?

Marcia V
HUH that is the kind I am having, surprised the VA is up to date on technology1 !

Nini L.
Great news!

Sherrie M.
No matter how bad a test may seem Have it done !!!! Early detection is important to save lifes !!!!! I don't have a cancer that could have been detected with a simple test !!!!

David J. Vining (author)
I often say that "Everyone needs colorectal cancer screening, but not everyone needs colonoscopy" to counter the claim that "If virtual colonoscopy finds a significant polyp, then you'll need to undergo colonoscopy, so why not have a colonoscopy in the first place?"

The fact is that in a screening population (people without symptoms like change in bowel habits, blood in stool, weight loss), 80% or more do not have any significant polyps that warrant colonoscopy for further evaluation, hence the benefit of virtual colonoscopy is that it is able to identify the 20% that actually need colonoscopy.

Less invasive means that virtual colonoscopy does not require sedation or expose the patient to the same risk of bowel injury as seen in colonoscopy.

Both exams still require a bowel cleansing so that a clear picture of the colon can been viewed, but as opposed to colonoscopy which uses a 5 foot long tube, virtual colonoscopy uses a small tube (3 inches) inserted into the rectum to distend the colon with carbon dioxide gas like a bicycle inner tube. We then scan the patient using a computed tomography (CT) scanner which takes 10 seconds, and later analyze the CT data with 3D imaging techniques to look inside the virtual colon. If a patient is in the minority and found to have a significant polyp, then we can refer the patient for same day colonoscopy so that a repeat bowel cleansing can be avoided.

There are certainly some controversies that still surround virtual colonoscopy, such as radiation dose (we use extremely low x-ray settings that are much less than a standard CT scan), insurance coverage (many insurers are now starting to cover virtual colonoscopy, particularly in patients that are considered to be high risk for colonoscopy), and the identification of disease outside to the colon (virtual colonoscopy is able to evaluate abdominal organs outside of the colon which can be a blessing or a curse depending how much additional evaluation is done on potentially insignificant findings).

Overall I think that the virtual colonoscopy procedure is an excellent screening option when performed at experienced centers, and since I am turning 50 this year, I will certainly have mine done around my birthday!

Screen! Screen! Screen!
Regardless of radiation, or aggravation of prep, or slight possibility of perforation, SCREEN!
My rectal cancer was found during routine colonoscopy in 2006. My breast cancer was found during routine mammogram in 2007. Both discovered early and corrected with surgery. Neither required chemo or radiation. Did require permanent colostomy and mastectomy - small price to pay for Life! Am grateful for routine screenings... hope VC becomes more widely available.
Keep working on effective prep procedures - thorough cleaning is difficult for both patient and Gastro Doc when dealing with peristomal hernia.

i was the one that did all the right things had
colonoscopy, had a few polops, redid colonoscopy 1 year later, colon cancer, had resection turns out stage 2, low grade doc not
much chance of comming back, susprise went to liver november of 2011, just finished
12 weeks of chemo, had ct today will get results Monday, to say i am scared, is an understatement. in meantime live had problem had to put tube in m stent in belly
btw, went to oncologist every 3 months for 2
years nothing ever showed up until the end of the two years with ct, A nurse at one hospital
told me that we are not in charge of anything

Guess She's Right

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