Bruce Brown, MD, a radiologist at University of Iowa Hospitals and Clinics and an associate professor talks about detecting colorectal cancer and a new screening method, called a virtual colonoscopy:
What is a colonoscopy?
A standard colonoscopy is an examination performed by passing a lighted, flexible tube containing a camera throughout the colon to examine the colon lining for abnormalities such as small areas of tissue overgrowth called polyps. These polyps can lead to cancer. While there are several methods of evaluating the colon for abnormalities, a colonoscopy is the most comprehensive.
When should people consider having a colonoscopy?
The American Cancer Society guidelines suggest that for an average risk person, cancer screenings such as colonoscopy should begin at age 50.
What are doctors looking for in a colonoscopy exam?
They are looking for polyps. It's now known that most colon cancers begin as bumps or polyps that are benign, and over five to 10 years, the polyps can change into cancer, so the doctor doing this colonoscopy is looking for these polyps so that he can remove them before they become cancerous.
So this makes early detection early?
It's very important. Removal of such polyps can remove the risk for cancer.
What is the common colonoscopy procedure like today?
The standard colonoscopy is performed after cleansing the colon and the patient then is sedated and monitored closely; and as I mentioned before, a flexible tube is inserted to view the inside surface of the colon. If a polyp is discovered, it can be removed during the procedure and examined under the microscope to check for any signs of change to cancer. The standard colonoscopy takes sedation, as we said; takes about 30 minutes; and is followed by a one to two hour period of recovery.
How does a virtual colonoscopy differ from the conventional method?
Virtual colonoscopy requires the same colon cleansing as the standard colonoscopy, but there is no need for sedation and no scope is inserted. Instead, the colon is inflated with CO 2 gas and imaged with very high resolution CT scanning, so that the shape of the inside of the colon can be reconstructed in three dimensions. Once the tubular shape is reconstructed using virtual reality, the radiologist is able to fly through the shape and examine it for polyps, much the same as a video game allows you to walk through a room or fly over a landscape. The whole examination takes about 10 minutes and there's no recovery time because there's no need for sedation, so people can go immediately about their daily activities. Of course if a polyp is detected that needs removal, it will have to be removed later.
Are there certain patients for whom the virtual colonoscopy may be the preferred method?
People in whom standard colonoscopy has failed, we use virtual colonoscopy. It may have failed because the endoscope can't be passed beyond a narrowed or a curved portion of the colon, or in some people who are on blood thinners and are at risk for being taken off of them.
Is the virtual colonoscopy as accurate in detecting cancer as the conventional colonoscopy?
In the best studies, the accuracy of virtual colonoscopy for detecting polyps is similar to standard colonoscopy. But there have been some studies where the accuracy is below that of standard colonoscopy.
The best summary of this is that when one considers having a virtual colonoscopy, patients should:
- Go to a center with a large experience with performing this exam
- Compared their techniques with standard colonoscopy
- Learn the accuracy of the test
At University of Iowa Hospitals and Clinics, the departments of Radiology, Internal Medicine, Family Medicine, are actively studying this technique and our preliminary results show that the way we do virtual colonoscopy gives us an accuracy similar to that with standard colonoscopy.
Is virtual colonoscopy used in screening or just in certain situations where colonoscopy has failed?
Studies such as ours in screening population are still ongoing and so for now, at UI Hospitals and Clinics, virtual colonoscopy is only used as a primary means of diagnosis in patients who have had a failed standard colonoscopy or can't be taken off anticoagulants, as I mentioned.
For now, all other patients at UI Hospitals and Clinics having a virtual colonoscopy are those enrolled in our study to determine the accuracy of virtual colonoscopy for screening. These are patients who have given their permission to have a virtual colonoscopy prior to having a standard colonoscopy, and that standard colonoscopy will have been ordered by their doctor for the usual indications. In this way, we're able to compare the results of virtual colonoscopy with the gold standard conventional colonoscopy and determine the accuracy of our virtual colonoscopy for screening.
If a listener wants to learn more about a virtual colonoscopy - where should they look or whom should they call?
We'd be happy to speak with anybody with questions. They should call our Virtual Colonoscopy Coordinator, David Kramer at 353-8067 at University of Iowa Hospitals and Clinics. |
