Virtual colonoscopy raises issues for further study

The American Society for Gastrointestinal Endoscopy (ASGE) has reacted with caution to claims of the benefits of computed tomography (CT) colonography, also referred to as virtual colonoscopy, compared to standard colonoscopy.

"Standard colonoscopy is still the most accurate test for detection and removal of cancer and pre-cancerous growths (polyps) in the colon," stated David Lieberman, MD, Oregon Health Sciences University, Portland VA Medical Center, Portland, OR. Dr. Lieberman is a past ASGE President and a noted expert in the area of colon cancer screening.

"Like any medical test, colonoscopy is not perfect, and some polyps may be present, but not detected," Dr. Lieberman explained. "However, most pre- cancerous polyps and virtually all cancers will be detected, and can usually be removed during the examination."

Virtual colonoscopy refers to the use of radiological (x-ray) techniques, including computed tomography (CT) and magnetic resonance imaging (MRI) scanning with computers, to produce pictures or images of the colon. It is "virtual" because the images are produced using radiation and evaluated on a computer screen, while a standard colonoscopy uses a thin, flexible lighted viewing tube (a colonoscope) that is threaded slowly through the colon to examine the lining for polyps.

Both standard and virtual colonoscopy requires a bowel preparation to cleanse the colon. Sedation is routinely used to reduce or eliminate discomfort associated with standard colonoscopy, but patients are not sedated for virtual colonoscopy.

Unlike standard colonoscopy, virtual colonoscopy only provides images of the colon, but does not allow for immediate biopsy or polyp removal at the time of the exam. Some abnormalities detected during virtual colonoscopy will require a standard colonoscopy for confirmation and management.

"The position of the ASGE Technology Assessment Committee is that CT colonography is a rapidly evolving technology with still rather varied results from the most recently published studies," said Bret T. Petersen, MD. Chair of the Technology Assessment Committee and director of endoscopy at the Mayo Clinic in Rochester, Minn. "A single recent study yielded very positive results, while most studies suggest CT colonography still has significant room for development and improvement before it becomes a primary screening tool for colorectal cancer."