Liver imaging reporting and data system category 4 observations in MRI: Risk factors predicting upgrade to category 5.

Purpose: To identify demographic and imaging features in magnetic resonance imaging (MRI) that are associated with upgrade of Liver Imaging Reporting and Data System (LI-RADS) category 4 (LR-4) observations to category 5 (LR-5), and to assess their effects on risk of upgrade and time to upgrade.

Materials And Methods: Institutional Review Board approval was obtained for this retrospective, dual-institution Health Insurance Portability and Accountability Act (HIPAA)-compliant study. Radiologists reviewed 1.5T and 3T MRI examinations for 181 LR-4 observations in 139 patients, as well as follow-up computed tomography (CT) and MRI examinations and treatment. A stepwise multivariate Cox proportional hazards model analysis was performed to identify predictive risk factors for upgrade to LR-5, including patient demographics and LI-RADS imaging features. Overall cumulative risk of upgrade was calculated by using the Kaplan-Meier method. The cumulative risks were compared in the presence/absence of significant predictive risk factors using the log-rank test.

Results: The independent significant predictive risk factors in the 56 LR-4 observations that upgraded to LR-5 were mild-moderate T hyperintensity (P < 0.001; hazard ratio = 1.84), growth (P < 0.001; hazard ratio = 3.71), and hepatitis C infection (P = 0.02; hazard ratio = 1.69). The overall 6-month cumulative risk of upgrade was 32.7%. The 6-month cumulative risk rate was significantly higher in the presence of T hyperintensity (P = 0.03; 48.1% vs. 25.4%).

Conclusion: For LR-4 observations, mild-moderate T hyperintensity, threshold growth, and hepatitis C infection are associated with significantly higher risk of upgrade to LR-5. Although mild-moderate T hyperintensity was the most useful risk factor for predicting upgrade, actual risk level was only mildly elevated, and the risk of upgrade associated with LR-4 observations is similar across subtypes.

Level Of Evidence: 3 Technical Efficacy: Stage 5 J. MAGN. RESON. IMAGING 2017;46:783-792.