There have been many recent reports about virtual colonoscopy testing to prevent colon cancer. These reports have stressed that virtual colonoscopy (more accurately called CT colonography) is non-invasive and “as good as” colonoscopy at finding large polyps. Both of these claims are essentially true but gloss over the benefits of colonoscopy over CT colonography.

First, why should anyone, particularly someone feeling good, consider ANY colon testing? Colon cancer is the number two cause of cancer deaths in America, second only to lung cancer. More women die of colon cancer than breast cancer and more men die of colon cancer than prostate cancer.

There are no early symptoms of colon cancer and no simple diagnostic tests. By the time you or your doctor know something is wrong, it is usually an advanced cancer that may not respond to radical surgery and chemotherapy. However, colon cancers start as benign polyps and slowly become more and more abnormal as they grow. They can be found and removed before they become cancerous. The risk of colorectal cancers and polyps starts to increase substantially after age 50 therefore screening for colorectal polyps and cancers is recommended starting at 50.

The techniques available to look for polyps include checking the stool for signs of blood, looking at the lining of the colon with x-ray testing or looking for polyps directly with scopes inserted into the rectum. Stool testing involves a chemical test of a stool sample to see if there may be small amounts of blood mixed into the stool. This is particularly important for polyps or tumors high in the colon. Any amount of blood in the stool should prompt more detailed examination to look for polyps or cancers. Stool testing needs to be combined with other testing to be reliable since many large polyps or tumors only bleed intermittently.

X-ray colorectal screening options include barium enema or the new CT colonography test. Barium enema coats the lining of the colon with barium and looks for changes in the shape of the lining that could indicate a polyp or cancer. A bowel preparation is required to remove stool from the colon. The best barium studies also have air added to the colon to make the lining easier to see on x-ray. The added air can be quite uncomfortable. Up to 10-15 percent of polyps can be missed and there is no opportunity to treat any abnormality found.

CT colonography is more accurate in finding polyps than a barium enema. A bowel prep is still required and the colon is again filled with air or carbon dioxide. Up to 35 percent of screening studies will find a polyp (or a portion of the colon wall that looks like a polyp) that will need to be investigated by colonoscopy.

Colonoscopy is a direct examination of the lining of the colon and rectum with a lighted flexible scope inserted into the rectum and guided through the entire length of the large intestine. A bowel preparation is required to remove stool from the colon. The study is done under sedation and most patients have no recollection of the study itself. Most polyps found during colonoscopy can be removed at the time of colonoscopy and sent for evaluation.

Other abnormalities of the surface that do not change the shape of the surface, such as colitis, can also be seen in very early stages by colonoscopy but are only seen in later stages on x-ray studies.

Colonoscopy is an invasive test and should be done by physicians specially trained in the procedure, such a gastroenterologists, colon and rectal surgeons and some general surgeons. Complications are uncommon but do occur. Some bleeding after polyp removal is common but significant bleeding is unusual.

The ability to remove polyps at the time of colonoscopy gives a definite advantage. One recent study on virtual colonoscopy discussed abnormal findings and referred patients for “immediate” colonoscopy. While this might be available at some university settings most communities do not have the ability to just add on another colonoscopy with no notice. An abnormal virtual colonoscopy finding then results in a colonoscopy at another time with a repeated bowel prep. Since most patients complain the most about the bowel prep, such a high possibility of doing it again is not relished.

Virtual colonoscopy is a great addition to the available screening tools. It is particularly helpful for patients who are very anxious, have increased risk for sedation or have had a difficult colonoscopy in the past. However, without the opportunity to remove polyps found it cannot be said to be equal to colonoscopy.