55 Evolutions in rectal cancer MRI staging and risk stratification in the Netherlands 4 – despite technological improvements in high-resolution imaging – it remains difficult to distinguish T2 tumors with desmoplasia from tumor stranding in early T3 tumors (6). Recently, the clinical significance of this distinction has been questioned as several pathology studies have demonstrated that it is mainly T3 tumors with more extensive invasion (>5 mm) beyond the rectal wall that constitute the group with a high risk of locoregional recurrence (7-11). The Mercury study group showed that high-resolution MRI can accurately determine the depth of extramural invasion (12) and a report by Taylor et al. showed that, by doing so, MRI can accurately identify tumors with a low-risk cT-stage (cT1-2 and cT3 with <5 mm perirectal invasion) that can safely be managed by surgery only (13). This subdivision of cT-stage according to the depth of invasion has meanwhile been adopted for risk stratification in several guidelines(1,3,14). The staging of lymph nodes has also evolved during the last decade. Although the clinical significance of node-positive disease (as assessed on imaging) is questioned by some (13,15), it is still included as a treatment determinant in many guidelines (1-5). Traditionally, positive nodes were mainly determined using size criteria, resulting in insufficient sensitivities and specificities ranging between only 55 and 78% (16,17). More recently, adverse morphologic features (heterogeneous signal, round shape, irregular border contour) have been adopted into guidelines as additional criteria to diagnose cN+ nodes which has improved the performance of MRI for nodal staging (3, 14, 18). A third development has been the increased acknowledgement of extramural vascular invasion (EMVI) as a relevant prognostic risk factor. Although not (yet) adopted in most guidelines as a main treatment determinant, there have been several reports showing that the presence of MRI-detected EMVI is a poor prognostic factor associated with an increased risk for metastases and impaired disease-free survival (15,19,20). In the most recent consensus guidelines on rectal MRI published by the European Society of Gastrointestinal and Abdominal Radiology (ESGAR) it is therefore now recommended to routinely include EMVI in the radiological staging report as a factor entailing more high-risk disease stage (14). Such developments warrant more precise radiological reporting and increase the need for structured reporting where all key elements to allow informed clinical decision making are sufficiently described. As with any new developments and guidelines updates, it takes time before these are fully acknowledged and implemented into general clinical practice. The aim of this study was to retrospectively analyze how the MRI reporting of rectal cancer has evolved over a period of ±seven years in the Netherlands (following guideline updates) by assessing trends in the use of structured reporting, evaluating how novel risk concepts such as cT3 substaging, updated nodal staging criteria, and EMVI have been adopted into routine reporting, and exploring its potential impact on treatment stratification.
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