Interobserver variability and diagnostic performance of gadoxetic acid-enhanced MRI for predicting microvascular invasion in hepatocellular carcinoma

Background: Accurate identification of microvascular invasion (MVI) in hepatocellular carcinoma (HCC) before treatment is critical for selecting a proper treatment strategy. Purpose: To evaluate the interobserver agreement and the diagnostic performance of the MRI assessment of MVI in HCC according to the level of radiologist experience. Materials and Methods: This retrospective study included 100 patients with surgically confirmed HCCs smaller than 5 cm who underwent gadoxetic acid-enhanced MRI between 2013 and 2016. Eight postfellowship radiologists (four with 7-13 years of experience [more experienced] and four with 3-6 years of experience [less experienced]) evaluated four imaging features (nonsmooth tumor margin, irregular rim-like enhancement in the arterial phase, peritumoral arterial phase hyperenhancement, peritumoral hepatobiliary phase hypointensity) and assigned the possibility of MVI. Interobserver agreement was determined by using Fleiss k statistics according to reviewer experience and tumor size (≤3 cm vs >3 cm). With reference standards of histopathologic specimens, the diagnostic performance in the identification of MVI was assessed by using receiver operating characteristic curve analysis. Results: In 100 patients (mean age, 58 years ± 10 [standard deviation]; 70 men) with 100 HCCs (mean size, 2.8 cm ± 0.9), 39 (39%) HCCs had MVI. The overall interobserver agreement was fair to moderate for the imaging features and their combinations (k = 0.38-0.47) and MVI probability (k = 0.41; 95% confidence interval: 0.33, 0.45). More experienced reviewers demonstrated higher agreement in MVI probability than less experienced reviewers (k = 0.55 vs 0.36, respectively; P = .002). Diagnostic performance of each reviewer was modest for MVI prediction (area under the receiver operating characteristic curve [AUC] range, 0.60-0.74). The AUCs for the diagnosis of MVI were lower for HCCs larger than 3 cm (range, 0.55-0.69) than for those less than or equal to 3 cm (range, 0.59-0.75). Conclusion: Considerable interobserver variability exists in the assessment of microvascular invasion in hepatocellular carcinoma using MRI, even for more experienced radiologists.