Diffusion-weighted MRI may support the identification of non-enhancing IDH wildtype astrocytoma

AIM: To determine if apparent diffusion coefficient (ADC) measurements permit the distinction of non-enhancing IDH mutant (IDHmut) from IDH wildtype (IDHwt) astrocytoma. BACKGROUND: Lack of Gadolinium contrast enhancement... [ view full abstract ]

AIM: To determine if apparent diffusion coefficient (ADC) measurements permit the distinction of non-enhancing IDH mutant (IDHmut) from IDH wildtype (IDHwt) astrocytoma. BACKGROUND: Lack of Gadolinium contrast enhancement represents a typical feature of low grade astrocytomas, but is increasingly considered an unreliable predictor of non-aggressive behaviour. The latest World Health Organisation (WHO) classification recognises a distinct subgroup of rapidly progressive gliomas (IDHwt astrocytoma) without histopathological grade IV characteristics. On molecular grounds, IDHwt astrocytomas constitute malignant neoplasms and are suspected to represent early glioblastomas (GBM). Their histology may be matched by initially innocuous imaging appearances, which could lead to misdiagnosis if a ‘watch and wait’ approach is adopted. METHODS: From a cohort of 58 WHO grade II/III astrocytomas (34 IDHwt/24 IDHmut), 22 non-enhancing tumours were selected. Manually obtained T2w volumetric segmentation masks were spatially registered (FSL) to ADC maps derived from standard DWI (b0-b1000). A quantitative analysis of diffusion values was performed blinded to molecular data and compared (Student’s t-test) for both groups. RESULTS: 13 IDHwt (6 WHO II/7 WHO III) and 9 IDHmut (6 WHO II/3 WHO III) astrocytomas were analysed. Maximum, mean and minimum ADC values for the IDHwt group were significantly lower (p < 0.01) than for the IDHmut group. CONCLUSION: ADC values derived from clinical DWI may reveal the aggressive nature of non-enhancing IDHwt astrocytomas, whereby mean ADC measurements are obtainable on most hospital imaging systems. Further study is required to determine, if a threshold value can be defined and to consider potential influences from WHO grade.