La coloscopie virtuelle joue-t-elle un rôle dans le dépistage du cancer colorectal?
Has virtual colonoscopy a role in screening for colorectal cancer?
Virtual colonoscopy (VC) represents a new promising methodology of noninvasive examination of the colon and rectum in patients screened for colorectal cancer or adenomas. The major advantages of this examination as compared to colonoscopy are 1) the limited risk, as no colonie perforation has been reported at this time and 2) the absence of need for sedation, although patient’s comfort does not appear to be optimal during prone and supine acquisitions of VC. The clinical usefulness of VC has to be estimated by comparison with available screening tests in different situations: Hemoccult and colonoscopy for general population screening and colonoscopy in case of patients at higher risk of colorectal cancer. The case of high risk patients appears simple: the perpolyp sensitivity of VC ranges between 40 and 100% for polyps more than 10 mm in maximal diameter, and drops for smaller lesions including flat adenomas that represent 30 % of all adenomas, and are a characteristic of these highrisk patients in case of HNPCC syndrome. Thus, VC does not compare favorably with colonoscopy in this group of atrisk patients. Regarding patients from the general population with a 4% cumulated risk of colorectal cancer, VC has a clearly higher sensitivity than Hemoccult for the diagnosis of cancer or adenomas. However, in a population context, increased specificity is a major aim in order to avoid unnecessary colonoscopies. The specificity of VC colonoscopy appears lower than that of Hemoccult, and most of all no prospective populationbased study has been performed: specificity would probably drop in such studies, as compared to selected population at higher risk of colorectal cancer and adenomas, for multiple reasons including the fear of missing adenoma or cancer. Moreover, despite this bias that overestimates the specificity of VC, costefficacy studies have shown that VC is at this time the more costly screening modality as compared to Hemoccult and colonoscopy. For all these reasons, indications of VC remain limited to incomplete colonoscopy (because of colonie loops or obstructive cancer) and examination of old and/or diseased patients not suitable for usual colonoscopy. These are the actual recommendation of the French Health Accreditation Agency (ANAES) as well as that of the American Society for Gastrointestinal Endoscopy (ASGE).
J.-C. SAURIN, G. GAUTIER, P.-J. VALETTE