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To differentiate between pineal germ cell tumour and pineoblastoma using apparent diffusion coefficient (ADC) values due to their overlapping imaging findings on magnetic resonance imaging (MRI). This retrospective study was conducted on 33 patients with pineal germ cell tumours and eight patients with pineoblastoma who underwent pretreatment MRI. Twenty-seven patients (21 with pineal germ cell tumour and six with pineoblastoma) were included for ADC measurement. The minimum and mean ADC values of the tumours were measured, with normalized tumour to control ADC ratios generated. The MRI characteristics of the tumours were evaluated. The mean and minimum ADC values, normalized mean and minimum ADC ratios of pineal germ cell tumours were significantly higher than those of pineoblastomas (all p <0.005). A cut-off value of 0.92 for the normalized mean ADC ratio was used to distinguish between pineal germ cell tumour and pineoblastoma and achieved an area under the curve of 0.95, sensitivity of 90.5%, specificity of 83.3%, and accuracy of 92.6%. An equal degree of contrast enhancement to the adjacent venous sinus was the only MRI characteristic that suggested the diagnosis of pineal germ cell tumour. The ADC values could help differentiate between pineal germ cell tumour and pineoblastoma, specifically when conventional MRI findings are indeterminate. • Pineal germ cell tumor and pineoblastoma have overlapping imaging findings on MRI. • ADC values could help differentiate between both tumor entities. • ADC values of pineal germ cell tumors were significantly higher than pineoblastoma. [ABSTRACT FROM AUTHOR]