23 Pearls and pitfalls of structured staging and reporting of rectal cancer on MRI 2 Table 3 Mean diagnostic accuracy and interobserver agreement for the main categorical staging variables Staging variables* Interobserver agreement Agreement with expert reference Reference standard (i.e. results of expert consensus reading; total n=75) Suboptimal (<60%) Moderate (60-80%) Good (>80%) I – Main staging variables used for risk stratification cTstage (cT0/1/2/3/4a/4b) 16% 40% 44% 69% 13 cT1-2, 39 cT3, 10 cT4a, 13 cT4b dichotomized cT-stage (≤cT3ab vs. ≥cT3cd) 17% 23% 60% 81% 33 low risk, 42 high risk cN-stage (cN0/1/2) 40% 32% 28% 60% 21 cN0, 26 cN1, 28 cN2 dichotomized cN-stage (cN0/ cN+) 9% 33% 57% 80% 21 cN0, 54 cN+ lateral N+ nodes (yes/no) 5% 19% 76% 88% 16 Yes, 59 No tumor deposits (yes/no) 7% 19% 75% 86% 13 Yes, 62 No MRF involvement (yes/no) 13% 23% 64% 82% 28 Yes, 47 No EMVI (yes/no) 9% 36% 55% 77% 30 Yes, 45 No Ia – Assessing the presence of high risk disease - Presence of any (≥1) high risk feature (≥T3cd, N+, tumor deposits, or EMVI) 9% 20% 71% 84% 60 Yes, 15 No II – Other staging variables morphology – shape (annular/ semi-annular/polypoid) 29% 31% 40% 67% 29 annular, 36 semiannular, 10 polypoid morphology – composition (solid/mucinous/mixed) 8% 27% 65% 79% 58 solid, 5 mucinous, 12 mixed relation to peritoneal reflection (above/below/straddling) 12% 23% 65% 77% 10 above, 41 below, 24 straddling sphincter invasion (yes/no) 5% 16% 79% 91% 16 Yes, 59 No Note, diagnostic accuracies represent the averages for all cases and readers combined. * The categorical staging variables cT3 substage (cT3ab vs cT3cd) and level of sphincter involvement (internal, intersphincteric plane, external sphincter) are not included in this table as these were only available for varying subsets of patients depending on assigned cT-stage and presence of sphincter invasion.
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