Virtual colonoscopy is an alternative to colonoscopy, and it is a technique that uses computerized tomography (CT) scanning to obtain images of the colon that are similar to the views of the colon obtained by direct observation through colonoscopy.
The day before the examination, the colon is cleaned out using laxatives. During the examination, a tube is inserted into the anus, then air is injected into the colon through it because the colon must be inflated when the CT scans are performed.
Virtual colonoscopy can find polyps "hiding" behind folds that occasionally are missed by colonoscopy, but it has several limitations:
- It has difficulty identifying small polyps (less than 5 mm in size) that are easily seen at a colonoscopy
- Flat cancers or premalignant lesions that are not protruding, that is, are not polyp-like
Also, virtual colonoscopy does not allow removal of polyps that are found and exposes individuals to a moderate amount of radiation. Because of these limitations, virtual colonoscopy has not replaced colonoscopy.