Prognostic Value of Subependymal Enhancement on Baseline MRI in Primary Central Nervous System Lymphoma.

Background/Objectives: Baseline magnetic resonance imaging (MRI) findings may provide prognostic information beyond existing clinical scoring systems in primary central nervous system lymphoma (PCNSL). This study evaluated whether baseline MRI findings predict survival in immunocompetent PCNSL and assessed the clinical implications of subependymal enhancement for treatment decision-making. Methods: Fifty immunocompetent PCNSL patients treated at a single institution (2010-2024) were retrospectively analyzed. Baseline MRI features, including subependymal enhancement, leptomeningeal spread, and ventricular involvement, were evaluated. Univariate and multivariate Cox analyses were performed for progression-free survival (PFS) and overall survival (OS), and the relationship between subependymal enhancement and chemoradiotherapy outcome was assessed by log-rank and interaction testing. Results: Median PFS and OS were 21.1 and 23.6 months, respectively. On multivariate analysis, subependymal enhancement was the strongest independent predictor of both PFS (hazard ratio [HR] 2.447, 95% confidence interval [CI] 1.164-5.145; p = 0.018) and OS (HR 2.607, 95% CI 1.279-5.313; p = 0.008), and leptomeningeal spread was independently associated with worse OS (HR 3.418, 95% CI 1.473-7.932; p = 0.004). Among patients with subependymal enhancement, chemoradiotherapy was associated with markedly improved PFS (33.5 vs. 3.0 months; p = 0.029) and OS (39.8 vs. 13.4 months; p = 0.029) and a higher complete response rate (100% vs. 0%) compared with chemotherapy alone. No significant chemoradiotherapy benefit was observed in patients without subependymal enhancement (PFS p = 0.332; OS p = 0.907). Conclusions: Subependymal enhancement and leptomeningeal spread independently predict survival in PCNSL. Although subependymal enhancement marks a poor-risk subgroup overall, patients with this feature who received chemoradiotherapy achieved markedly better outcomes, suggesting a role for early chemoradiotherapy in this population. Systematic MRI assessment at diagnosis may guide individualized treatment decisions beyond existing clinical scoring systems.