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Purpose: 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., Methods: 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)., Results: 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  mm 2 /s and 0.79-0.84 × 10 -3  mm 2 /s respectively., Conclusion: 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.

Purpose: Adult-onset neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder described mainly in the Japanese population, with characteristic DWI abnormalities at the junction between gray and white matter. We identify possible cases of NIID in the picture archive and communication system (PACS) of a tertiary neurological referral hospital in Singapore and describe their radiological features., Methods: The neuroradiology imaging database was reviewed using keyword search of radiological reports to identify patients who had "subcortical U fibre" abnormalities on DWI. MRI were retrospectively reviewed, and those fulfilling inclusion criteria were invited for skin biopsy to detect nuclear inclusions by light and electron microscopy., Results: Twelve Chinese patients (nine female; median age 70.5 years) were enrolled. Seven patients were being assessed for dementia and five for other neurological indications. In all patients, DWI showed distinctive subcortical high signal with increased average apparent diffusion coefficient (ADC), involving frontal, parietal, and temporal more than occipital lobes; the corpus callosum and external capsule were affected in some patients. On T2-weighted images, cerebral and cerebellar atrophy and white matter hyperintensity of Fazekas grade 2 and above were seen in all patients. Three patients underwent skin biopsy; all were positive for intranuclear hyaline inclusion bodies on either p62 staining or electron microscopy, which are pathognomonic for NIID., Conclusion: Previously undiagnosed patients with NIID can be identified by searching for abnormalities at the junction between gray and white matter on DWI in PACS and subsequently confirmed by skin biopsy. Radiologists should recognize the distinctive neuroimaging pattern of this dementing disease.