31 Pearls and pitfalls of structured staging and reporting of rectal cancer on MRI 2 (but also size and location) of tumour lesions from the endoscopy reports to allow proper clinically-informed image interpretation and reporting. Concerning the level of sphincter involvement, recent guidelines recommend that in distal tumours a coronal sequence parallel to the anal canal should be included to properly assess the relation between tumour and anal sphincter.1 In our current cohort, such a sequence was only available in 38% of the cases with suspected sphincter involvement. Our cohort dates back as far as 2010, which means that some scans were obtained using outdated study protocols, including suboptimal sequence angulation. Though a more in-depth analysis of the impact of image quality was beyond the scope of this paper, we acknowledge this as a limitation that may have introduced bias. There are some other limitations to our study design. First and foremost, as aforementioned, accuracy figures could only be estimated and were calculated using expert consensus as a standard of reference, considering the lack of histological confirmation for the majority of patients. Our study cohort was skewed towards advanced disease (77%) and direct correlation with pathology was only available for 17 cases. Moreover, not all staging variables were routinely reported in the pathology reports. Diagnostic confidence scores were furthermore missing for some of the staging variables. Image evaluation was performed using only T2-weighted sequences. Though DWI sequences are not routinely recommended for primary staging (mainly for restaging)1 they are also commonly included in primary staging protocols and might have been of benefit to aid in tumour detection and delineation. MRI scans in our cohort originate from one single country. Still, we believe that the sample derived from 10 different centres is representative for general clinical routine with representation of different vendors and common variations in clinical protocols. Finally, the number of patient cases assessed in this study was relatively small (n=75). This number was chosen as a minimum requirement to allow meaningful statistical analyses 26 while at the same time ensuring the feasibility that a large number of radiologists would complete all the scans within an acceptable timeframe. In conclusion, this study shows that – though structured reporting aims to accomplish uniformity in staging – there are still some pitfalls that need to be acknowledged as they may result in insufficient staging reproducibility. Suggestions for improvement include more simplified, dichotomized risk stratification of cT- and cN-stage, adoption of confidence scores for items with low reproducibility, embedding more specific definitions for image interpretation into staging templates, and ensuring state-of-the-art image protocols.
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