Accuracy of CT colonography for colorectal cancer screening.

* Data are from Johnson et al.1 To the Editor: Johnson et al. (Sept. 18 issue)1 discuss the use of computed tomographic (CT) colonography as a noninvasive option in screening for colorectal cancer, with optical colonoscopy and histologic review serving as the reference standard. Two important points merit discussion. First, sensitivities that are reported in the “perpolyp” analysis for lesions measuring 5 to 9 mm in diameter are deceiving since values are reported as “greater than or equal to” a certain size. With this method, a higher sensitivity for larger lesions falsely elevates the sensitivity for smaller ones. Using data abstracted from Tables 3 and 4 in the article, we calculated the number of adenomas or cancers of each specified size (Table 1). For example, for the specified size of 5 mm, 32 of 104 known lesions were detected by CT colonography, yielding a sensitivity of 31%. Our analysis revealed a sensitivity of 46% (113 of 246) for adenomas measuring 5 to 9 mm and of 57% (81 of 142) for those measuring 6 to 9 mm in size in aggregate. This factor is important because the field is maturing to the point at which specific treatment is predicated on the size of individual lesions.2 The second critical point has to do with the generalizability of the study’s results, since only 15 of 20 highly experienced radiologists were allowed to participate. If CT colonography were widely implemented, could the average radiologist participate? Don C. Rockey, M.D. Samir Gupta, M.D.