The Prerequisite: Faecal Tagging

As described in the previous chapter, preparing the colon is a sine qua non to adequately perform state-of-the-art CT colonography. The option of an intensive preparation to obtain a colon as clean and dry as possi ble has been approved in 2005 in a consensus statement by several CT colonography experts and is currently still the method of choice to prepare the colon for CT colonography (Barish et al. 2005). Indeed, in a well-distended, clean, and dry colon, con-spicuity of tumoral lesions should be at its best. However, the real world is not that simple. Indeed, two large trials of >600 patients have shown that an intensive cathartic preparation might be insufficient in obtaining good results of polyp detection (Cotton et al. 2004; Rockey et al. 2005). Both the Cotton and Rockey trials obtained very disappointing results with a sensitivity of <60% for adenomas ≥ 6 mm. Of the many flaws these two trials have been inflicted with, the lack of fecal tagging was considered a major shortcoming (Ferrucci and Working Group on CT C olongraphy 2005a and author reply Ferrucci 2005b). Furthermore, to date, the U.S. Department of Defence trial obtained the best results of polyp detection in a large asymptomatic population of 1,233 patients at average risk for colorectal cancer using a preparation combining a low-residue diet and oral laxatives with fecal tagging (Pickhardt et al. 2003a, b). Since the publication of this landmark study, fecal tagging was gradually accepted as an indispensable part of the colonic preparation for CT colonography. This propensity for fecal tagging was confirmed in the ESGAR-CTC consensus statement published in 2007 (Taylor et al. 2007) and in the recent ACRIN 6664 trial fecal tagging was part of the preparation (Johnson et al. 2008).