Virtual Colonoscopy Virtual colonoscopy uses data from computed tomography (CT) to generate two- and three-dimensional images of the colon and rectum. Due to the inclusion of CT imaging, this procedure has also been referred to as computed tomographic colonography (CTC). Internal images of the colon and rectum can be stored, viewed on a monitor, or printed on film. These high-resolution images are used to create a three-dimensional model of the colonic lumen that can be navigated in an interactive fashion, resembling the view seen through a colonoscope, which involves inserting a fiber optic camera into the colon for a visual inspection.

Virtual colonoscopy is a minimally-invasive procedure that requires no intravenous administration of sedatives or analgesics. The day before the CT scan, bowel cleansing is performed. At the time of the CT scan, a thin tube is inserted into the rectum and air or carbon dioxide is introduced into the colon to distend the bowel, allowing polyps to be differentiated from the normal surface. Adenomatous polyps, which are the precursors to colon cancer, may be identified using this technique. Colonic perforation has been reported due to over inflation of the colon. Patients who are suspected of having inflammatory bowel disease may not be good candidates due to the potential risk of bowel perforation (Torres, 2007).

Researchers have proposed the use of this minimally-invasive procedure as an alternative to existing screening tests (i.e., colonoscopy) for CRC, and as a means of diagnosing patients with contraindications that would make the use of conventional colonoscopy unsafe: fulminant colitis, acute diverticulitis, perforated viscus, or a recent myocardial infarction. Other relative contraindications include chronic, stable irritable bowel syndrome, chronic abdominal pain, acute diarrhea, upper gastro-intestinal tract bleeding or melana with a demonstrated upper gastrointestinal tract source, metastatic adenocarcinoma or unknown primary site in the absence of colonic signs, or symptoms when the colonoscopy would not influence patient management (Beers, 2007).

Virtual colonoscopy does permit visualization of the entire colon, even in the presence of stenosing lesions (Torres, 2007). CT can also be used in high-risk patients as a “one-stop” test to detect not only the primary tumor but synchronous colon lesions, and to provide additional information regarding regional and distant metastatic disease, depth of wall invasion and precise localization of the lesion within the colon prior to surgery (Harford, 2006; O’Hare, 2006). Inadequate colonic inflation or excess fluid retained within the colon may lead to false-positive reports due to the misinterpretation of findings. However, advances in imaging techniques using fecal tagging and fluid subtraction have enhanced the clarity of the images that are documented (Harford, 2006; O’Hare, 2006). Another drawback of this diagnostic procedure is that a traditional colonoscopy is still needed in order to biopsy or remove any lesion/polyp that is found (Torres, 2007; Feldman, 2006).