Morphologic patterns of noncontrast-enhancing tumor in glioblastoma correlate with IDH1 mutation status and patient survival.

Glioblastomas with a substantial proportion of noncontrast-enhancing tumour (nCET) have a variety of imaging appearances. We aimed to determine whether glioblastomas demonstrating a substantial proportion (>33%) of nCET can be sub-classified by different morphologic pattern of nCET. We then assessed whether this improves the ability of MRI to predict isocitrate dehydrogenase-1 (IDH1) mutation status and whether this has prognostic significance independent of IDH1 mutation status. Pre-operative MRIs of patients with a new diagnosis of glioblastoma were reviewed. Tumours with >33% nCET were sub-classified by the dominant morphologic pattern of nCET: mass-like expansion, white matter dissemination, grey matter dissemination or a combination. IDH1 mutation status (by immunohistochemistry) and survival were compared for each pattern. 153 patients met the inclusion criteria, of whom 34 patients demonstrated >33% nCET. 10 patients had a significant mass-like component, either as the dominant pattern (n=4) or as part of a mixed pattern (n=6). The 10 patients with a significant mass-like component had longer survival than those without (median 387days, compared to 241days), though this was not statistically significant (p=0.242). Three patients had R132H-IDH1 mutations and >33% nCET, and all three had a mass-like component. Using the presence of a mass-like component of nCET for predicting IDH1 mutation status improved the positive predictive value, specificity and overall accuracy of MRI. Classification of nCET by morphologic pattern improves the ability of MRI to predict IDH1 mutations and may provide useful prognostic information.