[Virtual CT colonoscopy. Examination technique, limitations and perspectives]

Virtual CT-colonoscopy is a post-processing method which allows for reconstruction of inner bowel surface structures from helical CT datasets. The reconstructed images simulate the views which are known from fiberoptic endoscopy. Since colorectal cancer is the second main cause of death in USA and Europe today and since recent screening recommendations are often ignored by the public, a non-invasive or minimal-invasive procedure for colonic evaluation would offer some benefits. Virtual CT-colonoscopy generally involves three essential steps: patient preparation with cleansing of the bowel and administration of an air enema, helical CT-examination by using appropriate scan parameters, and interactive 3D rendering of the volume data-set. Although recent studies have demonstrated that polypoid lesions of about 5 mm size are well detectable and although virtual colonoscopy offers many advantages over fiberoptic endoscopy, some technical and clinical limitations must still be noted. Thus, the current inability of virtual colonoscopy to provide texture and color leads to problems in identifying flat lesions; the presence of retained or adherent fecal matter may result to false positive diagnosis and collapsed segments of bowel may cause problems as they cannot subsequently be evaluated during image reconstruction. Virtual endoscopy is still in its infancy and further technical and clinical developments are necessary. Virtual CT-colonoscopy may then prove to be equal or superior to colonoscopy in sensitivity and specificity for polyp detection and be able to reduce the number of unnecessary colonoscopic procedures.