A new study led by a doctor from the Mayo Clinic in Arizona in the US, finds that “virtual colonoscopy”, known more formally as computerized tomographic CT colonography, is comparable to standard colonoscopy for people aged 65 and over. The American College of Radiology Imaging Network study was published online before print on 23 February in the journal Radiology.

The finding clears up a question unanswered by a 2008 New England Journal of Medicine study that suggested virtual coloscopy was as good as standard colonoscopy, but it did not specifically analyze its performance with older patients.

Now Dr. C. Daniel Johnson Chair of the Department of Radiology at Mayo Clinic, and colleagues, show that the procedure is not just for younger people.

Colonoscopies are procedures that look for signs of pre-cancerous growths or polyps, cancer and other diseases in the large intestine.

In a standard colonoscopy, which is normally used with people aged 50 and over, a trained doctor slides a long flexible tube with a camera into the patient’s rectum to view the colon. Patients have to take laxatives to empty the colon, and undergo sedation, before having the procedure. They generally go home afterwards and rest for the remainder of the day.

Virtual colonoscopy using computerized tomography or CT images to look for signs of disease such as polyps, in the colon.

The patient still has to undergo colon cleansing, but requires no sedation and no tubes and cameras are inserted into the colon. There is just a minimal insertion of an enema tip into rectum that blows carbon dioxide into the colon to inflate it, and then the patient passes through a machine that takes a series of x-ray images of the large intestine.

Rather like assembling a loaf of bread, the x-ray image “slices” are then put together to make a 3D view of the entire colon and rectum.

In the standard procedure, if the doctor sees any polyps, he or she can remove them, using a wire loop that passes through the tube. For this reason, the procedure carries a higher risk of bowel perforation.

The concern that remained following the 2008 NEJM study that indicated virtual colonoscopy was as good as the standard one, was the fact polyps tend to occur more in older people.

But in this new study, when Johnson and colleagues used data from the 2008 study to evaluate the performance of CT-based colonoscopy in patients over 65, compared to those aged 50 to 65, they found no statistical difference in effectiveness of CT-based colonoscopy between the two groups.

The data came from the National CT Colonography Trial, where 2,600 patients over the age of 50 underwent both virtual and optical colonoscopies at 15 centers across the US.

The results showed that virtual colonoscopy based on CT, was highly accurate at detecting intermediate (6 to 9 mm) sized and large (above 1 cm) sized polyps. And because the vast majority of patients will not be found to have a polyp, there is no need to go any further.

Johnson said in a press statement:

“We found no statistical difference in the diagnostic performance between the two patient groups.”

“”This is good information for patients of any age, as they can consider CT colonography as a valid option for colorectal cancer screening.”

In fact, only 12% of the patients found to have a polyp at the CT-based colonoscopy stage would need to have a standard colonoscopy where the polyp can be located and safely removed.

Since most colon cancers develop from polyps, it is finding and removing these pre-cancerous growths that is most likely to help wipe out this disease.

Johnson said:

“The key isn’t so much the modality, the key is getting screened.”

“We hope that this additional, less-invasive option for cancer screening will lead more people to get screened and will ultimately result in fewer deaths from colorectal cancer,” he added.

Johnson said the decision to get screened should be an individual one, informed by discussion with health care professionals.

He said virtual colonoscopy may suit a patient who:

  • Experiences difficulty with the standard procedure,
  • Has an obstructed colon,
  • Is taking anti-coagulants,
  • Or is just unwilling to undergo the standard procedure.

Colorectal cancer is the second leading cause of death from cancer in the US and the third most frequently diagnosed cancer.

Even though the benefits of screening are clear and well-known, studies show that most Americans aged 50 and over are not having it.

Experts cite cost and lack of access to health care as the main reasons.

Written by Catharine Paddock PhD