Decoding MRI Presentation of Primary Central Nervous System Diffuse Large B Cell Lymphoma: A Novel Subgroup...

Primary central nervous system Epstein-Barr Virus-negative diffuse large B-cell lymphoma (PCNSL) of immunocompetent patients is an aggressive extranodal lymphoma with challenging imaging features. In a large histopathologically-confirmed cohort, we aimed to update conventional MRI characteristics of PCNSL, identify radiological subtypes, and explore early survival differences across subgroups.

We retrospectively evaluated the consecutive cohort of immunocompetent patients diagnosed with PCNSL who presented to our Lymphoma Unit between 2010 and 2023, enrolling patients with available pre-biopsy 1.5T or 3.0T brain MRI including T1-weighted, T2-weighted, FLAIR, DWI, and post-contrast T1 sequences. Two neuroradiologists independently assessed lesion characteristics (number, location, morphology, volume, signal).Unsupervised hierarchical clustering was applied to identify radiologically-homogeneous subgroups. Associations between subgroup and progression-free/overall survival were assessed using Cox regression in prespecified models adjusted for age, sex, International Extranodal Lymphoma Study Group (IELSG) score and induction regimen.

We enrolled 100 patients (median age 63.9 years, 51% female). Lesions were multifocal in 55% and involved only supratentorial brain in 66%, both supratentorial and infratentorial compartments in 28% and only infratentorial in 6%. Morphology was predominantly mass-like (75%). Median volume was 5.5 mL (IQR 2.0 - 14.9). Relative to brain cortex, T2 signal was hypointense in 63%, isointense in 21%, and hyperintense in 16%; T1 was isointense in 50%, hypointense in 44%, and hyperintense in 6%. Enhancement was solid in 74%, patchy in 7%, closed-ring in 4%, mixed solid-patchy in 15%. Hierarchical clustering identified four subgroups according to radiological characteristics: 1) classical mass-forming (40%): supratentorial, T2-hypointense, solidly enhancing masses; 2) CSF surface-predominant (22%): ependymal, intraventricular, or cortical-pial locations with homogeneous enhancement; 3) infiltrative (20%): small enhancing foci with extensive T2/FLAIR hyperintensity and perivascular enhancement; and 4) atypical mass-forming (18%): large, heterogeneous lesions enriched in necrosis and haemorrhage. Adjusted overall survival differed across subgroups in exploratory analyses (p=0.02), with higher mortality in CSF surface-predominant and infiltrative patterns and lower mortality in the atypical mass-forming group compared with classical mass-forming.

This study updates MRI features of PCNSL and identifies four radiological subgroups, offering a basis for future molecular correlations and prognostic stratification.