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Ankara University Medical School, Ibn-i Sina Hospital, Ankara, Turkey
WEB—This is a Web exclusive article.
We are astonished at how the authors found the results of the two studies "similar." When one reads and compares the two articles with modest care, he or she will quickly grasp the major differences in the methodology used and, perhaps more important, the results reached.
Unlike the study of Covey et al. [2], we evaluated separately the variations involving the main portal vein ramification and right portal vein ramification. In the Results section, we presented our findings separately. To summarize, 34.5% of our patients showed variations only in the main portal vein ramification. This is higher than most of the former studies, including that of Covey et al. [2], in which the relevant figure is 22% (the sum of 9% with type 2 variation and 13% with type 3 variation, as presented in Table 1 of their study). More specifically, although 9.5% of our patients had type 2 main portal vein anatomy, similar to the 9% in the older study, 23.5% had type 3 anatomy, very much different from the 13% reported by Covey et al. When we total the frequencies of type 2 and type 3 anatomy in our study and their study, we find 33% and 22%, respectively. If these figures are similar, then Drs. Covey and Brown are right in their arguments.
Drs. Covey and Brown must have failed to recognize the separate presentation of right portal vein branching variations in our study. Briefly, 22 of 131 patients with type 1 main portal vein anatomy had variant right portal vein branching, which was 11% of the total study group. If we add this 11% to the 34.5% of patients with variant main portal vein branching, we reach 45.5%, which is also quite different from the 35% reported by Covey et al. [2]. The types of variations involving the right portal vein branch are also different in the two studies, but a detailed discussion of these variations is beyond the scope of this letter.
We believe these major differences might have resulted from the different methodology used in the two studies. We evaluated the thin overlapping axial sections obtained with a helical MDCT scanner and 3D reconstructions. In their article, Covey et al. [2] have already admitted that the study was potentially limited by its retrospective nature and the use of thick nonoverlapping 7-mm axial slices that did not allow 3D reformatting. Notwithstanding this admission, Drs. Covey and Brown, in their letter, appear to ignore the potential benefit of 3D images in the detection of subtle variations or the differentiation of those variations from each other. Although the different genetic backgrounds of the two populations may have had an effect, we believe the differences might also have resulted from the 3D reconstructions routinely obtained in our study.
Finally, we apologize for not including their valuable study in our reference list and thank the authors for giving us this opportunity to reveal the striking disparity between the two studies.
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