Medical Informative Booklets
Medical Imagery (Screening of Colorectal Cancer)
Virtual Colonoscopy
Colorectal neoplasia is the second cause of cancer-related deaths in the United States and in Europe.
The detection of precancerous polyps and their removal is said to reduce mortality related to colon cancer over 80%.
Moreover, the five-year survival rate of colon cancer, early detected and treated, at an early stage, is about 90%.
Unfortunately, very few people accept a screening examination. In 2002, a new non invasive technique (non endoscopic) has been developed to explore the colon by CT, the virtual colonoscopy. 
The exam is preceded by a preparation (click) with the objective to eliminate faeces present in the colon or at least to mark them by ingesting baryum during the meals the day before.
The exam consists of 2 acquisitions of images lasting 20 seconds each, first resting on the belly and then on the back, following intravenous injection of a spasmolytic and inflation of air through the rectum, in order to completelydistend the colon. There is no need to be fasting and the exam will not need iodinated contrast injection.
After image acquisition, the 600 to 800 slices generated by the exam are displayed on a workstation which enables to reconstruct the images in two dimensions (fig 2) and to obtain three-dimensional endoscopic views (fig 3).
According to several studies, virtual colonoscopy had a sensitivity of 95% to detect 10mm-large polyps, which is the real risk threshold, and 75 to 89% to detect 6 to 9 mm-large polyps. Detection of invasive cancers is close to 100%. If a significant anomaly is found, a second examination will be made through a traditional endoscopic exam allowing the resection of polyps or the performance of a biopsy.
In addition to detection, virtual colonoscopy is also indicated in case of contra-indication or incomplete conventional colonoscopy. This exam also allows to explore the colon proximal to obstructive lesion , unreachable by endoscope.
A huge advantage of the virtual method, is the visualisation on the native slices of all the other intra-abdominal organs. According to a study, 9% of virtual colonoscopy detected important extra-colic anomalies : liver cancer, pancreatic cancer, genito-urinary cancer, urinary stones, vesicular lithiasis.
As X-rays are used, pregnant women may not be screened (however, irradiation used in virtual colonoscopy is well below baryum enema : approximately 3,6 mSv compared to 9,2 mSv respectively).
As for every radiological exam, virtual colonoscopy (also called colon-CT), must be prescribed by a medical doctor. Its price is the equivalent of a CT of the abdomen.
Virtual colonoscopy is a new non invasive technique, well-tolerated without any need of sedation, which enables to explore the colon completely, and which performances outdo those of baryum enemaand are similar to the traditional optical colonoscopy, with, moreover, the possibility to visualise the other abdominal organs.
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