Current guidelines recommend colorectal cancer screening for all average-risk individuals beginning at age 50. Colonoscopy has been considered the gold standard as it permits detection and removal of pre-cancerous polyps. A normal colonoscopy for an average-risk individual can clear them for 10 years. If small pre-cancerous polyps are detected and removed, the recommended interval for polyp surveillance is shorter (generally 5 years, but this can be even shorter based on the size and number of polyps).
A “virtual colonoscopy” is a specialized CT scan of the colon, which can be used as an alternative test for colorectal cancer screening. While it can be as good as colonoscopy at detecting large polyps and cancers, it can miss smaller polyps. Also, the patient must still take the same bowel preparation that is necessary for a colonoscopy. No sedation is required for a virtual colonoscopy, but a rectal tube is inserted and large amounts of air are insufflated into the colon, which can result in discomfort. If a suspicious lesion is seen on virtual colonoscopy, a standard colonoscopy must then be performed to further investigate and likely remove the polyp. While the exposure is small, a virtual colonoscopy exposes the patient to radiation. A virtual colonoscopy may have a role in colorectal cancer screening, but it does not yet appear ready to replace conventional colonoscopy.