29 Pearls and pitfalls of structured staging and reporting of rectal cancer on MRI 2 Discussion In this study we evaluated uniformity in structured reporting of rectal cancer among an international group of 21 radiologists. When looking at the main staging variables used for risk- and treatment stratification, good results were achieved for dichotomized assessment of high versus low-risk cT-stage and cN0 vs N+ stage, lateral nodes and tumour deposits, and MRF involvement. These variables resulted in good (>80%) interobserver agreement in the majority of patient cases. Less favourable results were found for multicategorical cT- and cN-staging, and for assessing EMVI. We observed a clear significant positive correlation between diagnostic confidence and the agreement of study readers with an expert standard of reference (which was used as a surrogate standard to estimate diagnostic accuracy, considering the lack of pathologic correlation for most study cases and variables). This correlation is an interesting finding considering that template reports tend to force radiologists to assign a specific stage or category, even if they are unsure about their diagnosis, which is a potential drawback of structured reporting. Our results show that this uncertainty can lead to substantial variations in staging. Given the potential impact on treatment, it might be better to incorporate the level of confidence into structured reporting templates to better inform risk-based clinical decision making during multidisciplinary team discussions, at least for those items that are poorly reproducible and strongly influenced by variations in diagnostic confidence. Interestingly, the dichotomized classification of cT-stage into high risk (≥cT3cd) versus low risk (≤cT3ab) resulted in better IOA than the multicategorical cT-stage classification as defined the TNM staging manual.4 Some guidelines, like those from the National Comprehensive Cancer Network (NCCN)18, use cT3 disease as a key risk factor indicating a need for neoadjuvant treatment. However, several studies have shown that MRI often overstages T2 tumours as T3 resulting in potential overtreatment.19–21 Other guidelines consider early stage T3 disease (T3ab with ≤5 mm extramural invasion) as low risk, with comparable prognostic outcomes and treatment implications as T2 tumours.22,23 Our results show that this dichotomous classification results in better agreement and is therefore perhaps better suited to guide risk and treatment stratification. Assessment of T4a and T4b disease remains a problem area with poor IOA. As illustrated in Figure 3, there were several cT4a cases with simultaneous MRF involvement that were understaged as T3 MRF+. Apparently readers tend to choose either MRF or peritoneal (cT4a) invasion, rather than acknowledging that the two may co-occur. Moreover, some readers may mistake anterior invasion of the peritoneum above the level of the peritoneal reflection as MRF invasion (Figure 5AB). These issues were also demonstrated as pitfalls that require further teaching in a recent international survey study.12 It could be helpful
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