T1‐Hyperintense Cystic Renal Masses: MR Subtraction Imaging May Improve Interobserver Agreement and Diagnostic Performance in the Bosniak Classification

BACKGROUND: T1-hyperintensity in cystic renal masses (CRMs) complicates Bosniak classification assessment due to inherent signal interference from hemorrhage and proteinaceous content, potentially obscuring enhancement visibility. PURPOSE: To investigate whether MR subtraction imaging improves interobserver agreement and diagnostic performance in the Bosniak classification of T1-hyperintense CRMs. STUDY TYPE: Retrospective. POPULATION: A total of 139 consecutive patients (mean age, 50 ± 12 years; 97 males) with 141 T1-hyperintense CRMs were included, consisting of surgically confirmed 133 lesions and clinically diagnosed 8 benign CRMs that were stable during follow-up (≥ 5 years). FIELD STRENGTH/SEQUENCE: 1.5/3 T. fat-saturated T2-weighted imaging, diffusion-weighted imaging, unenhanced, and triphasic dynamic contrast-enhanced T1-weighted imaging (T1WI). Subtraction images were generated automatically by subtracting unenhanced from triphasic contrast-enhanced T1WI. ASSESSMENT: Six radiologists (half less experienced) independently classified all T1-hyperintense CRMs using the Bosniak classification (v2019) in two sessions, with and without subtraction imaging. A 1-month washout period was implemented between sessions, and the order of cases was re-randomized. Interobserver agreement and diagnostic performance were evaluated in all experienced and less experienced readers. STATISTICAL TESTS: Weighted κ statistics assessed interobserver agreement. Diagnostic performance (the area under the curve [AUC], sensitivity, specificity) was compared using Delong and McNemar tests. Statistical significance was defined as p < 0.05. RESULTS: Subtraction imaging significantly improved interobserver agreement in all radiologists (weighted κ = 0.62 vs. 0.46), and less experienced radiologists (3-5 years of experience, weighted κ = 0.63 vs. 0.42), though not significantly among experienced radiologists (10-15 years of experience, weighted κ = 0.61 vs. 0.52; p = 0.051). Less experienced radiologists showed significantly higher AUC (0.865 vs. 0.804), sensitivity (88.9% vs. 75.5%), and specificity (88.2% vs. 72.5%) with MR subtraction imaging. DATA CONCLUSION: MR subtraction imaging may improve overall interobserver agreement in the Bosniak classification of T1-hyperintense CRMs. Furthermore, it could improve diagnostic accuracy and interobserver agreement among less experienced radiologists. EVIDENCE LEVEL: 4. TECHNICAL EFFICACY: Stage 2.