Atypical radiological findings of primary central nervous system lymphoma.

Primary central nervous system lymphoma (PCNSL) presenting with atypical radiological findings often leads to delayed diagnosis. We aim to characterize the radiological features and apparent diffusion coefficient (ADC) values of PCNSL with atypical neuroimaging presentation in our local population. We retrospectively reviewed all patients with histological diagnosis of CNS lymphoma at our tertiary center from 2005 to 2016. We screened all initial pre-treatment MRIs and excluded cases with typical imaging findings of contrast-enhancing lesions without intra-lesional susceptibility and central non-enhancement. Additional exclusion criteria included (i) relapsed PCNSL, (ii) secondary CNS lymphoma, and (iii) positive HIV status. Two independent raters scored MRI and CT scans at presentation. We computed ADC values in the tumors by 2 methods: single region of interest (ROI1) and multiple ROI (ROI2). Sixteen (25.4%) of 63 patients with CNS lymphoma met inclusion criteria. There were 8 men; median age was 61 (range 22–81) years. Histological diagnoses were diffuse large B cell lymphoma (n = 14) and intravascular lymphoma (n = 2). Fifteen (93%) patients had enhancing lesions (5 solitary; 10 multifocal); most enhancing lesions had T1 hypointense (67%) and T2 mixed (53%) signals, and 6 (40%) had central non-enhancing regions. Nine (56%) patients had lesions with susceptibility. Using the ROI methods, median values for minimum ADC and mean ADC ranged 0.65–0.71 × 10–3 mm2/s and 0.79–0.84 × 10–3 mm2/s respectively. PCNSL with atypical radiological features represented one-fourth of our histologically diagnosed lymphoma cases; low ADC values in atypical lesions should prompt clinicians to consider early biopsy for definitive diagnosis.