Virtual colonoscopy, also known as computed tomography (CT) colonoscopy, is an imaging technique that uses X-rays to create images of the colon. These images are assembled by a computer to produce a three-dimensional representation of the colon on a computer screen (hence virtual), which is then examined by a gastroenterologist. The technique is less invasive than conventional colonoscopy since the X-rays are applied from an external source and no physical colonoscope is required – although a thin tube still needs to be inserted a short distance into the rectum to slightly inflate the colon for better visibility. Virtual colonoscopy is mainly used to detect tumors, polyps and diverticulitis, which it does with high accuracy. The main advantage of virtual colonoscopy is its non-invasive character. The procedure itself is not painful and requires therefore no sedation. Accordingly, patients can return to their normal daily activities immediately after the test, which takes only about 20 minutes. Despite these advantages, virtual colonoscopy has two major limitations. Firstly, since no physical colonoscope is used, any found polyps cannot be removed in the same session, and a second conventional colonoscopy session is required for this. Secondly, inflamed areas of the colon cannot be detected or sampled by virtual colonoscopy, i.e. no biopsy can be taken. Because of these limitations, the method is less suitable in the context of IBS where direct viewing of the colonic wall is necessary to differentiate between IBS and other inflammatory conditions such as IBD or colitis. Virtual colonoscopy is also not suitable for pregnant women, as the X-rays may cause an abnormality to the unborn child.
The Preparation for a virtual colonoscopy requires a bowel-cleansing regimen similar to that of conventional colonoscopy. This includes laxatives and a restrictive diet the day before the examination. The procedure itself is similar to a CAT scan. As a patient, you will be placed on a moveable examination table and slid into the doughnut-shaped CT scanner which takes the images. The nurse or physician will insert a thin tube a short distance into your rectum to slightly inflate the bowel for better visibility. This may be somewhat uncomfortable but is not painful. During the scanning, you will be asked to change position and hold your breath to obtain clear images from various angles. Pillows and straps may also be used to help you hold the correct position. The scanning is painless and takes about 20 minutes. After the scan, you will be able to resume all normal activities.
The obtained images will be reviewed by a radiologist and discussed with you immediately of forwarded to your general practitioner. Should any abnormalities be observed, a conventional colonoscopy may be required to further examine any suspicious areas, collect tissue samples or remove polyps.
In patients suffering from IBS only, virtual colonoscopy will not detect any abnormalities as IBS does not cause any visible alterations in the gastrointestinal tract. In such patients the persistence of abdominal complaints along with negative findings of the examination will be considered a confirmation of IBS.
In summary, virtual colonoscopy is a technique that uses x-rays to obtain images of the entire gastrointestinal tract. Its main advantage is the non-invasive and thus painless execution. The method is suitable to detect gastrointestinal tumors and polyps and may be considered for screening of individuals with an increased risk of such conditions. In the context of IBS, the method is less suitable as it cannot detect inflamed tissue and does not allow collection of tissue samples. Accordingly, virtual colonoscopy cannot be used to differentiate between IBS and several other conditions with similar symptoms. Here, classical colonoscopy remains the most reliable diagnostic method for patients with suspected IBS.