The "purfling sign": a new imaging marker for the diagnosis of primary CNS lymphoma.

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To investigate whether the "purfling sign," a new imaging marker, could distinguish primary central nervous system lymphoma (PCNSL) from brain gliomas, and its diagnosis value for preoperative identification of PCNSL. Contrast-enhanced MR imaging features of 161 PCNSL and 161 glioma were evaluated by 2 independent neuroradiologists: (1) the presence/absence of the "purfling sign"; (2) the presence/absence of lesion necrosis and cystic changes; and (3) the heterogeneity of tumor parenchymal enhancement. Inter-rater agreement was assessed with Cohen's kappa (κ), and the diagnostic performance of the "purfling sign" in identifying PCNSL was investigated. Three separate institutional validation cohort (including 177 PCNSL and 177 glioma patients) was analyzed to validate the diagnostic performance of the "purfling sign." Among the test set, the inter-rater agreement of the "purfling sign" was high (κ = 0.907), while that for the other features was only good [κ = 0.663-0.691]. The purfling sign was present in 89 (55.28%) lymphoma and 13 (8.07%) glioma cases with a specificity of 91.93%, a sensitivity of 55.28%, a positive predictive value (PPV) of 87.25%, and a negative predictive value (NPV) of 67.27% for the diagnosis of PCNSL. Furthermore, the tumors presenting with the "target sign" were all PCNSL (16/16,100%), with a specificity and PPV of 100%. Analysis with the validation cohort, 85.09% cases with a positive "purfling sign" were PCNSL (p < 0.0001; PPV = 85.09%, NPV = 66.67%, specificity = 90.40%, sensitivity = 54.80%). With a robust inter-rater agreement, our study found that the "purfling sign" on enhanced MR represents a high specific imaging marker for the preoperative diagnosis of PCNSL. This noninvasive marker may aid in the guidance of the clinical diagnosis and treatment processes of PCNSL.