30 Chapter 2 to include the anatomical boundaries between MRF and peritoneum, and the distinction between cT3 MRF+ and cT4a MRF+ disease as specific staging options in template reports, aiming to increase radiologists’ awareness and ultimately uniformity in staging. Future studies should focus on establishing the benefit of further training and teaching in reducing interobserver variability in such pitfall cases. Similar to cT-staging, results for cN-staging were also better when dichotomized (into cN0 vs cN+). Considering the known limitations of MRI, radiologists should perhaps refrain from detailed cN-staging and limit themselves to estimating the risk for cN0 or cN+ disease, including a level of confidence to support their findings. Results for assessment of lateral nodes and tumour deposits were remarkably good, especially when considering the concerns voiced in recent reports on the lack of validated imaging criteria.12 These good results can likely be partly explained by the low prevalence of positive lateral nodes and tumour deposits in our cohort and the fact that agreement with our expert standard or reference was particularly high (88%-93%) to diagnose these negative cases. Results for assessment of EMVI were lower than expected (>80% interobserver agreement reached in only half of the study cases). Although image-detected EMVI has been acknowledged as an important prognostic factor for some time, it was introduced into reporting guides and templates more recently and is still less routinely reported than other risk factors such as TN-stage and MRF.1,7 Some readers may therefore still be going through a learning curve and experience difficulties with less straightforward cases such as Figure 3. In line with a previous report that showed relatively low sensitivity and PPV (62-67%) and high specificity and NPV (88-89%)17, radiologists in our study were also better in assessing EMVI- than EMVI+ tumours. Further teaching, and inclusion of specific published grading systems to diagnose EMVI+ disease into reporting templates, could be beneficial to further improve uniformity in the staging of EMVI. When looking at the other staging items, tumour morphology (in particular the distinction between annular, semi-annular and polypoid tumours) and level of sphincter involvement showed the poorest results. Describing the tumour morphology is mainly relevant as polypoid tumours typically have a better prognosis compared to (semi-) annular tumours with a more extensive invasive margin.24 Disease-focused panel recommendations from the Society of Abdominal Radiology (SAR) define a polypoid tumour as a tumour with a pedicle or stalk.25 A later report by Golia Pernicka et al. suggested to redefine the polypoid definition to ≤¼ wall circumference attachment and a visible pedicle.24 Future guidelines and reporting templates should perhaps adopt such more specific definitions to improve uniformity in the radiological assessment of tumour morphology. Moreover, radiologists should be properly informed about the morphology
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