Will Colonoscopy Meet Its Match?
May 30, 2001 -- More than 90% of cancers of the colon and rectum, called colorectal cancer, can be cured if detected and treated early enough, but many adults are reluctant to undergo screening for the disease because it involves a procedure with a high "ugh!" factor: colonoscopy.
This standard technique for getting good video images of the colon, or large bowel, is an uncomfortable procedure in which a flexible tube carrying a light and a miniature camera on its tip is passed up through the rectum. But because of the twists and turns in the digestive tract, it is often hard for doctors to snake the tubes around bends, and they frequently have to puff in jets of air to inflate the bowel and help the camera get through narrow passages. The procedure causes so much discomfort that it is usually performed with the patient under sedation or anesthesia.
An alternative procedure called virtual colonoscopy is being developed in which the entire colon is imaged on computer using a fast CT scan method. In a study of 300 patients who underwent a virtual colonoscopy, followed by a standard colonoscopy, the virtual procedure was able to detect 90% of all large polyps -- abnormal growths from which nearly all colon cancers arise -- that were seen on standard colonoscopy. Virtual colonoscopy also correctly identified all eight patients with colon cancer, report Judy Yee, MD, and colleagues at the University of California, San Francisco (UCSF).
The virtual procedure does not require patients to be sedated or put under anesthesia, and it can be performed in less than one minute, compared with about 30-60 minutes -- plus recovery time -- required for standard colonoscopy.
"The hope is that this technique would be used not to completely replace conventional colonoscopy, but that it would eventually increase the number of patients who are screened for colon cancer who would otherwise go unscreened," says Yee, assistant professor of radiology at UCSF and chief of CT and gastrointestinal radiology at the San Francisco VA Medical Center.
The standard technique does have a distinct edge over its virtual cousin: When physicians spot polyps during standard colonoscopy exams, they can remove them and retrieve the tissue for biopsy using special grasping and cutting tools mounted on the scope. Patients who have suspicious lesions detected by the noninvasive technique must then undergo standard colonoscopy. But having a less-intimidating procedure available may bring more people through their doctor's door for screening as well as identify more patients who need to be treated.
"Right now, the number of Americans being screened for colon cancer is less than 40% of the patients who should be screened, so there is a huge number of people out there who are just unscreened," Yee tells WebMD. "The hope is that using this noninvasive technique, with basically no risk, that we can increase the number of patients screened and we will find more lesions."