25 Pearls and pitfalls of structured staging and reporting of rectal cancer on MRI 2 Figure 2 Example of a case that was staged as cT4a by expert consensus because of involvement of the peritoneum on the left anterior side, above the level of the anterior peritoneal reflection (arrowheads in A). There is simultaneous focal involvement of the MRF below the level of the anterior peritoneal reflection (arrow in B). The study readers unanimously scored this case as MRF+ (100%), but 81% of readers scored it as cT3 and only 19% as T4a. cN-staging Agreement with the expert reference for dichotomized assessment of cN0/N+ stage was 80%, which was considerably higher than for multicategorical cN-staging as cN0/1/2 (agreement 60%). The number of detected positive mesorectal lymph nodes varied widely, as reflected by the very low group agreement in defining the number of suspicious mesorectal nodes (α=0.05).
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