Qualitative MRI features in the differentiation between primary and secondary CNS lymphoma

Differentiating between primary CNS lymphomas (PCNSL) and secondary CNS lymphomas (SCNSL) remains a challenge in imaging. The aim of this study was to differentiate histopathologically-proven PCNSL and SCNSL by using 25 qualitative VASARI and five other MRI features.

MRIs of 31 cases (19 PCNSL and 12 SCNSL) obtained between January 2010 and February 2022 were retrospectively reviewed. Two blinded readers independently evaluated images without knowledge of clinical data or whether CNS lymphoma was primary or secondary. The findings of each reader were recorded to assess interreader agreement. The results of two readers were evaluated by a senior neuroradiologist to reach a consensus. A statistical analysis was performed on the collected data.

Most VASARI features showed no statistically significant differences between the two groups, except for two features. Tumor location exhibited a statistically different distribution between PCNSL and SCNSL groups (p = 0.036). Proportion of edema was greater in the PCNSL group compared to the SCNSL group (p = 0.049). Among other MRI features, infratentorial involvement was more frequent in the SCNSL group (p = 0.014), while notch sign was more commonly detected in the PCNSL group (p = 0.027). Inter-reader agreement for VASARI features ranged from moderate to almost perfect, and for other MRI features, it ranged from fair to almost perfect.

Despite the challenges in distinguishing imaging features of PCNSL and SCNSL; frontal lobe location, a higher proportion of edema and the presence of a notch sign may indicate PCNSL, while infratentorial involvement may suggest SCNSL.