Virtual Colonoscopy Still Under Study

< December 15, 2004 > -- A future trends report published in the journal of the American Gastroenterological Association (AGA), Gastroenterology, concludes that "virtual colonoscopy," or CT colonography, has significant promise.

However, the technology is still evolving and the results of CT colonography for screening are variable.

Guidelines of professional societies and government sources underscore the importance of screening for all individuals 50 years of age and older.

Several Reliable Tests Are Available

Currently, there are a number of tests that may be used to screen for colorectal cancer, the third leading cause of cancer in both men and women in the US.

Approved tests include barium enema, fecal occult blood test (FOBT), flexible sigmoidoscopy (FSIG), and colonoscopy. Each screening option has advantages and disadvantages.

"No colorectal cancer screening test is perfect," says AGA President Dr. Emmet B. Keeffe. "CT colonography is currently not the most accurate or convenient test, but may in the future be included in the mix of colorectal cancer screening options available to patients and physicians.

"While the virtual aspect of the test sounds appealing, it isn't a panacea," Dr. Keeffe says. "CT colonography is associated with discomfort and still requires rigorous preparation, often the most daunting challenge to compliance."

Many practical issues still need to be addressed, including standardization of test performance, patient preparation, and interpretation of test results before CT colonography can be recommended for routine clinical practice, Dr. Keeffe notes.

The AGA assembled a task force of gastroenterologists, radiologists, and epidemiologists to undertake a critical analysis of available information on the capabilities of CT colonography and to consider its potential role in colorectal cancer screening.

The task force reviewed the results of recent clinical trials and quantitative mathematical models pertaining to CT colonography. Limitations in the evaluation of CT colonography included variation in results of clinical trials and limited data on its use in routine clinical practice.

One limitation of CT colonography is that the test cannot consistently detect flat polyps or those smaller than one centimeter. The clinical importance of these types of polyps remains largely uncertain but given that a small number might harbor malignancy, most clinicians advise their removal, the AGA reports.

Thus a significant proportion of patients undergoing CT colonography might need a second procedure if it is necessary to remove all small growths.

Preparing for the Test Challenges Patients

One of the largest barriers to patient compliance for colorectal cancer screening is the bowel cleansing preparation required prior to the test.

Patients must undergo similar bowel preparation for CT colonography as they do for traditional colonoscopy.

However, progress is being made in the development of a minimal prep or prep-less CT colonography examination. Improvements in CT colonography stool tagging to "electronically cleanse" the colon are still under study.

Because CT colonography is a new technology, it is not yet widely available or covered by health insurers. There is also need for a larger pool of physicians to perform CT colonography and interpret results of the test.

Standardization of test performance and results interpretation are necessary, the AGA states. 

"Patients should not put off screening for colorectal cancer and polyps," says Dr. Keeffe. "Adults age 50 and older should talk with their physician about the screening tests currently available to them."

Always consult your physician for more information.

Online Resources

American Gastroenterological Association

Centers for Disease Control and Prevention (CDC)

National Institutes of Health (NIH)

National Women's Health Information Center

Find a Physician at
St. John's Mercy or call our Physician Referral Service at 314-FOR-DOCS.  

For more information on Colorectal Cancer, please visit health information modules on this Web site.

Screening for Colorectal Cancer

Screening methods for colorectal cancer, for people who do not have any symptoms or strong risk factors, include the following:

digital rectal examination (DRE) - a physician or healthcare provider inserts a gloved finger into the rectum to feel for anything unusual or abnormal.

fecal occult blood test - checks for hidden (occult) blood in the stool. It involves placing a very small amount of stool on a special card, which is then tested in the physician's office or sent to a lab.

In addition to the above, screening also includes one of the following:

sigmoidoscopy - a diagnostic procedure that allows the physician to examine the inside of a portion of the large intestine, and is helpful in identifying the causes of diarrhea, abdominal pain, constipation, abnormal growths, and bleeding. A short, flexible, lighted tube, called a sigmoidoscope, is inserted into the intestine through the rectum. The scope blows air into the intestine to inflate it and make viewing the inside easier.

colonoscopy - a procedure that allows the physician to view the entire length of the large intestine, and can often help identify abnormal growths, inflamed tissue, ulcers, and bleeding. It involves inserting a colonoscope, a long, flexible, lighted tube, in through the rectum up into the colon. The colonoscope allows the physician to see the lining of the colon, remove tissue for further examination, and possibly treat some problems that are discovered.

barium enema with air contrast (Also called a double contrast barium enema.) - a fluid called barium (a metallic, chemical, chalky, liquid used to coat the inside of organs so that they will show up on an X-ray) is given into the rectum to partially fill up the colon. An X-ray of the abdomen shows strictures (narrowed areas), obstructions (blockages), and other problems.

Colorectal cancer screening guidelines for 2004 from the American Cancer Society for early detection state that beginning at age 50, both men and women should follow one of the examination schedules below:

• fecal occult blood test (FOBT) every year
  
  
• flexible sigmoidoscopy (FSIG) every five years
  
  
• annual FOBT and FSIG every five years
  
  
• double-contrast barium enema every five years
  
  
• colonoscopy every 10 years
  

People with any of the following colorectal cancer risk factors should begin screening procedures at an earlier age and be screened more often:

• strong family history of colorectal cancer or adenomatous polyps in a first-degree relative, in a parent or sibling before the age of 60 or in two first-degree relatives of any age
  
  
• family with hereditary colorectal cancer syndromes, such as familial adenomatous polyposis (FAP) and hereditary nonpolyposis colon cancer (HNPCC)
  
  
• personal history of colorectal cancer or adenomatous polyps
  
  
• personal history of chronic inflammatory bowel disease

Always consult your physician for more information.