Tumor apparent diffusion coefficient combined with the lipid-to-creatine ratio for preoperative differentiation of primary central nervous system lymphoma from high-grade glioma: a single-center diagnostic model development and internal validation study

Abstract

Background and purpose Primary central nervous system lymphoma (PCNSL) and high-grade glioma (HGG) may share overlapping conventional MRI appearances. We developed and internally validated a parsimonious model combining tumor apparent diffusion coefficient (ADC) and the lipid-to-creatine ratio (Lip/Cr), compared it with every single predictor, and evaluated the secondary contribution of proximal peritumoral ADC. Materials and methods This retrospective, availability-based cohort included 83 consecutive eligible patients with pathologically confirmed PCNSL (n = 38) or HGG (n = 45) who underwent pretreatment 3.0-T MRI with diffusion-weighted imaging and proton magnetic resonance spectroscopy. Four prespecified logistic models were evaluated. Internal validation used 2,000 stratified bootstrap resamples with standardization repeated within each resample. Distribution-appropriate summaries, paired incremental performance, empirical calibration, sensitivity analyses, and exploratory decision-curve analysis were reported. Results Tumor ADC was lower and Lip/Cr was higher in PCNSL than in HGG (both P < 0.001). The tumor ADC plus Lip/Cr model achieved an apparent AUC of 0.925 and an optimism-corrected AUC of 0.918 (95% CI, 0.868–0.980); the corrected Brier score was 0.114 (95% CI, 0.073–0.160). Relative to Lip/Cr alone, the corrected changes were small and uncertain (ΔAUC, 0.021; 95% CI, −0.039 to 0.055; ΔBrier, −0.020; 95% CI, −0.044 to 0.023). Adding proximal peritumoral ADC also produced small and uncertain changes (ΔAUC, 0.004; 95% CI, −0.039 to 0.023; ΔBrier, −0.005; 95% CI, −0.018 to 0.027). Findings were directionally stable after log transformation of Lip/Cr and restriction of the HGG comparator to IDH-wildtype glioblastoma. Conclusions Tumor ADC plus Lip/Cr showed favorable exploratory internal-validation performance, but superiority over Lip/Cr alone was not established. The model requires multicenter external validation with prespecified MRS quality control and should support, rather than replace, expert interpretation and histopathologic confirmation.