Virtual colonoscopy for colorectal cancer screening: current status

Abstract

Computed tomography colonography (CTC) (also known as 'virtual colonoscopy') is a noninvasive method of imaging the colon using helical CT. Although CTC has been shown to be useful for certain clinical indications, it has not yet been endorsed as a colorectal cancer screening test. The purpose of this article is to review the current status of CTC for colorectal cancer screening. CTC is an accurate method to detect colonic polyps and to select patients who would benefit from colonoscopy. The major advantages of CTC over conventional colonography include its relatively low risk and greater tolerance by patients. In this article, the CTC procedure and results of clinical trials are reviewed, as well as potential pitfalls related to CTC performance and interpretation. Finally, radiation dose, the discovery of incidental extracolonic findings with CTC, bowel preparation methods, and computer-aided diagnosis are addressed.

Figure 1

Sigmoid polyp. 2D transaxial (a) and 3D endoluminal (b) images demonstrate a 1 cm sessile sigmoid polyp.

Figure 2

Sigmoid mass and polyp. (a) A sagittal 2D image demonstrates a lobulated mass in the sigmoid colon. (b) The corresponding 3D endoluminal image shows a nearby 9 mm sessile polyp in addition to the mass.

Figure 3

Pedunculated descending colon polyp. (a) A transaxial 2D image acquired with the patient in the supine position shows a 9 mm polyp (arrow) that appears sessile. (b) A transaxial 2D image acquired with the patient in the prone position demonstrates that the polyp (arrow) arises from a haustral fold and is pedunculated. (c) The corresponding 3D endoluminal view with the patient in the prone position also demonstrates the pedunculated nature of the polyp.