Evidence of supratentorial white matter injury prior to treatment in children with posterior fossa tumours using diffusion MRI

Background Paediatric brain tumour survivors can have neurocognitive deficits that negatively impact their quality of life, but it is unclear if deficits are primarily caused by treatments, such as radiotherapy, or manifest earlier due to the tumour and related complications. The aim of this work is to characterise white matter injury caused by brain tumours, unrelated to treatment effects, and explore heterogeneity in these white matter abnormalities between individual patients. Methods We used diffusion tensor imaging (DTI) and Neurite Orientation Dispersion Diffusion Imaging (NODDI) to assess white matter injury in 8 posterior fossa tumour patients. A novel one-against-many approach was used by comparing an individual patient to 20 age- and sex-matched healthy controls to assess variability in white matter abnormalities between the posterior fossa tumour patients. White matter was analysed at presentation (prior to treatment), post-surgery (24-72 hours after surgery), and at follow-up (3-18 months after surgery). Results We demonstrate white matter abnormalities in 5 posterior fossa tumour patients before treatment, likely related to tumour-induced hydrocephalus, which persisted after treatment. White matter changes were complex and patient-specific, and group-based comparisons with control sub-jects may fail to detect these individual abnormalities. Conclusions Identifying pre-treatment white matter injury in posterior fossa tumour patients highlights the importance of personalised assessment of brain microstructure, which should be considered in minimising neurocognitive deficits to improve patient quality of life.