• Jae Seok Bae, Se Hyung Kim, Bo Yun Hur, Won Chang, Juil Park, Hye Eun Park, Jung Ho Kim, Hyo-Jin Kang, Mi Hye Yu, and Joon Koo Han.
• Department of Radiology, Seoul National University Hospital, 101 Daehak-ro, Jongno-gu, Seoul, 03080, South Korea.
• Eur Radiol. 2019 Aug 1; 29 (8): 4379-4388.

ObjectivesThis study was conducted in order to determine the prognostic value of MRI for extramural venous invasion (EMVI) in rectal cancer compared to pathology and to assess the diagnostic performance of multireaders.MethodsWe retrospectively enrolled 222 patients (M:F = 148:74; mean age ± standard deviation, 61.5 ± 12 years) with histopathologically proven rectal cancers who underwent preoperative MRI between 2007 and 2016. Among them, 74 patients had positive EMVI on pathology (pEMVI) and 148 patients had negative pEMVI. Three radiologists with 7 (reviewer 1), 3 (reviewer 2), and 1 (reviewer 3) year of experience in rectal MR imaging determined the presence of EMVI on MRI (mrEMVI) using a 5-point grading system. Using histopathologic results as the reference standard, radiologists' performances were analyzed and compared with receiver operating characteristic (ROC) analysis. For assessment of interobserver variation, intraclass correlation coefficients (ICC) were used. Lastly, Kaplan-Meier estimation and Cox proportional hazard models were used for survival analysis.ResultsThe area under the ROC curve (AUC) was highest in reviewer 1 (0.829), followed by reviewer 2 (0.798) and reviewer 3 (0.658). Differences in AUCs between reviewer 1 or 2 and reviewer 3 were statistically significant (p < 0.001). ICC was substantial between reviewers 1 and 2. Overall survival (OS) was significantly different according to the positive circumferential resection margin, adjuvant treatment, and the presence of mrEMVI, but not by the presence of pEMVI.ConclusionsFor experienced radiologists, the diagnostic performance of mrEMVI was good, resulting in better prediction of OS than with pEMVI, with substantial interobserver agreement.Key Points• When read by experienced radiologists, MR can provide reliable diagnostic performance in assessing EMVI for patients with rectal cancer. • Positive mrEMVI is an adverse prognostic factor of overall survival and may influence the clinical decision-making.

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