Gyriform infiltration as imaging biomarker for molecular glioblastomas

Background Molecular glioblastomas (i.e. without the histological but with the molecular characteristics of IDH-wild-type glioblastoma) frequently lack contrast enhancement, which can wrongly lead to suspect a lower-grade glioma. Herein, we aimed to assess the diagnostic value of gyriform infiltration as an imaging marker for molecular glioblastomas. Methods Two independent investigators reviewed the MRI scans from patients with newly diagnosed gliomas for the presence of a gyriform infiltration defined as an elective cortical hypersignal on MRI FLAIR sequence. Diagnostic test performance of this sign for the diagnosis of molecular glioblastoma were calculated. Results A total of 426 patients were included, corresponding to 31 molecular glioblastoma, 294 IDH-wild-type glioblastoma, 50 IDH-mutant astrocytoma, and 51 IDH-mutant 1p19q-codeleted oligodendroglioma. A gyriform infiltration was observed in 16/31 (52%) molecular glioblastoma, 40/294 (14%) IDH-wild-type glioblastoma, and none of the IDH-mutant glioma. All the 56 gyriform-infiltration-positive tumors were IDH-wild-type and all but two had a TERT promoter mutation. The inter-rater agreement was good (κ = 0.69, p < 0.001). The sensitivity, specificity, positive predictive value and negative predictive value of the presence of a gyriform infiltration for the diagnosis of molecular glioblastoma were 52%, 90%, 29%, 96%, respectively. The median overall survival was better for gyriform-infiltration-negative patients compared to gyriform-infiltration-positive patients in the whole series and in patients with non-enhancing lesions (n = 95) (25.6 vs 16.9 months, p = 0.005 and 20.2 months vs not reached, p < 0.001). Conclusion Gyriform infiltration is a specific imaging marker of molecular glioblastomas that can help distinguishing these tumors from IDH-mutant lower-grade gliomas.