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Objectives: To determine the diagnostic accuracy of conventional MRI in detecting tumour invasion of advanced intraocular retinoblastoma and to correlate ADC values with high-risk prognostic parameters.Method: The sensitivities, specificities, positive predictive values (PPV), negative predictive values (NPV) and accuracies of MRI in detecting tumour-extent parameters of 63 retinoblastomas were determined. Furthermore, ADC values were correlated with high-risk prognostic parameters.Results: MRI detected postlaminar optic nerve with a sensitivity of 73.3% (95% CI 44.9-92.2%) and a specificity of 89.6% (77.3-96.5%), while the specificity for choroidal invasion was only 31.8% (13.9-54.9%). Likewise, MRI failed to predicted early optic nerve invasion in terms of low sensitivity and PPV. In contrast, scleral and ciliary body invasion could be correctly excluded with high NPV. ADC values were significantly lower in patients with undifferentiated tumours, large tumour size, as with optic nerve and scleral invasion (all p < 0.05). However, no correlation was found between ADC values and the degree of choroidal or ciliary body infiltration. Additionally, ADC values were negatively correlated with Ki-67 index (r = -0.62, P = 0.002).Conclusions: Conventional MRI has some limitations in reliably predicting microscopic infiltration, with the diagnostic efficiency showing room for improvement, whereas ADC values correlated well with certain high-risk prognostic parameters for retinoblastoma.Key Points: • Conventional MRI failed to predicted microscopic infiltration of the retinoblastoma. • Scleral and ciliary body invasion could be excluded with high NPV. • ADC values correlated well with some high-risk pathological prognostic parameters. [ABSTRACT FROM AUTHOR]