Validation of the “purfling sign” for differentiating primary central nervous system lymphoma from high-grade glioma: a retrospective multicenter cohort study

Background The study aimed to evaluate whether the imaging marker “purfling sign” can reliably distinguish primary central nervous system lymphoma (PCNSL) from high-grade glioma and systematically assess its diagnostic performance, differential utility and clinical value. Materials and methods This retrospective multicenter cohort study included 209 patients with PCNSL and 285 patients with glioma who underwent contrast-enhanced magnetic resonance imaging (CE-MRI). Two board-certified neuroradiologists independently reviewed CE-MRI features including lesion number, “purfling sign”, tumor necrosis and cystic changes, and tumor parenchymal enhancement heterogeneity, with inter-rater reliability assessed using Cohen’s kappa coefficient. Group comparisons were performed between the PCNSL group and the glioma group, and the diagnostic performance of the “purfling sign” was evaluated by calculating its sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy, with 95% confidence intervals (CIs) reported for all metrics. Results PCNSL and glioma showed significant between-group differences in lesion number, tumor necrosis and cystic changes, and tumor parenchymal enhancement heterogeneity (all P < 0.001). The purfling sign also differed significantly between groups ( P < 0.001): it was detected in 100 PCNSL cases (47.80%) and 34 glioma cases (11.93%), yielding a sensitivity of 47.85% (95% CI: 41.1%–54.6%), specificity of 88.07% (95% CI: 84.3%–91.8%), PPV of 74.63% (95% CI: 67.3%–82.0%), NPV of 69.72% (95% CI: 64.9%–74.5%), and diagnostic accuracy of 71.05% (95% CI: 67.1%–75.0%) for PCNSL diagnosis. Notably, the target sign was exclusive to PCNSL (14/14, 100%), resulting in 100% specificity and PPV. In terms of inter-rater agreement, excellent consistency was achieved for the purfling sign and tumor necrosis and cystic changes (κ= 0.982 and 0.869, respectively), with good agreement for parenchymal enhancement heterogeneity (κ= 0.709). Conclusion Consistent with prior findings, the “purfling sign” serves as a valuable auxiliary diagnostic indicator for differentiating PCNSL from high-grade glioma, thereby facilitating improved diagnostic confidence and providing supportive evidence for clinical management.