Virtual Colonoscopy Doesn't Replace Conventional Type

Q:  Please tell me about virtual colonoscopy. My doctor found polyps during my last colonoscopy five years ago, and now she has scheduled a follow-up test. I am dreading it.

My doctor says the conventional colonoscopy is better than the virtual colonoscopy, but I would really rather avoid drinking all that stuff!

A:  Virtual colonoscopy sounds good, doesn't it? But let's compare. In both conventional and virtual colonoscopy, the doctor is looking for polyps (which could turn into cancer) and colon cancer.

Conventional colonoscopy is established as an effective screening tool that may prevent colon cancer by taking out polyps that would have turned into cancer, and by and finding any cancer early, when it is more likely to be curable.

Conventional colonoscopy involves using a long tube with a camera and a light on one end (the "scope"). The scope is inserted into the rectum and advanced to inspect the colon. During this procedure, you receive medications for pain and to keep you sleepy, which generally work so well that most people do not complain about the procedure itself.

What most people complain about, and it seems you are included, is the "prep." Usually, the preparation is to drink about a gallon of a medicated beverage that forces out the contents of the colon - that is, forces out the stool.

This means many trips to the bathroom and lots of drinking until you are cleaned out. This step is necessary because colonoscopy is not effective if stool is in the way of a clear view.

Virtual colonoscopy involves a scan like a CAT scan in the x-ray department, and it is relatively new. Just like the conventional colonoscopy, your colon has to be free of stool, but the prep is somewhat different and often better tolerated.

While the virtual colonoscopy doesn't use a scope, it does require a bit of air to be injected into the colon so that the colonic walls do not fall against each other, thereby obscuring a polyp. Also, with virtual colonoscopy, you wouldn't get pain or sedation medications, which may mean a bit of discomfort. But as soon as it's done, you are free to go about your day instead of needing a ride home, as after conventional colonoscopy.

The real problem with virtual colonoscopy is that, if polyps were found, you would still need a conventional colonoscopy to remove them. This occurs frequently: in people older than 60, about 40% to 50% have polyps that may turn into cancer.

W. Dennis Foley, MD, FACR is a Professor of Radiology at the Medical College of Wisconsin. He tells me that virtual colonoscopy is the choice for patients who have significant bleeding problems or who are at high risk for conventional colonoscopy complications, and when conventional colonoscopy cannot be completed (for example, if there is an obstruction). In other cases, insurance might not pay for it.

Julie L. Mitchell, MD, MS, is an Assistant Professor of Medicine at the Medical College of Wisconsin. She practices at the Froedtert & The Medical College of Wisconsin General Internal Medicine Clinic - East. Her column appears in the Milwaukee Journal-Sentinel.