Colorectal cancer

Colorectal cancer is the second deadliest type of cancer in developed countries. Early disease detection greatly improves the survival rate. In its July 2016 report, US Preventive Services Task Force (USPSTF) included CT colonography (CTC – virtual colonoscopy) as an equally valuable method for colorectal cancer screening among seven acceptable screening options. Approved screening methods are colonoscopy, fecal immunochemical test (FIT), for occult bleeding, sigmoidoscopy + FIT and CT colonography. Fecal immunohistochemical DNA test, guaiac test for occult bleeding and sigmoidoscopy by itself are inferior in comparison with the first four methods. With proper bowel preparation, new CT colonography studies have shown CTC sensitivity and specificity in discovering lesions that are 6mm or larger to be comparable to colonoscopy (sensitivity: 73-98% and specificity: 89-90%).

CT colonography (virtual colonoscopy) is done with the help of modern CT devices that enable the imaging of colon convolutions after air or carbon dioxide spreading. Prerequisite for the examination are thoroughly cleansed bowels using a high amount of liquid in combination with laxative. After computer imaging, reconstructions of inner bowel surface are also analyzed.

Main advantages of CTC are its minimal invasiveness, short procedure time and the capability to image all parts of the bowel. Disadvantages are exposure to low radiation level, inability to take samples and the potential remains of stool in the bowel that disables quality examination, same as in case with classic colonoscopy. Colonoscopy is required for the final histological evaluation or polyp removal.

1. US Preventive Services Task Force. Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement. JAMA. 2016;315(23):2564-2575. doi:10.1001/jama.2016.5989

Click here to download the official USPSTF brochure.