T2-FLAIR mismatch sign for diagnosis of 1p19q non-codeleted or ATRX mutant astrocytoma

Abstract Aims The World Health Organisation (WHO) classification of adult gliomas has undergone significant revision in recent years, with current emphasis on the role of the molecular biomarkers IDH, 1p19q, ATRX, and p53 for classification of glioblastoma, astrocytoma, and oligodendroglioma. When correctly applied the T2-FLAIR mismatch sign is reported to have 100% specificity for WHO grade II or III IDH mutant 1p19q non-codeleted astrocytoma. We sought to verify this classic imaging-molecular correlate in our cohort at a single tertiary level neurosurgical referral centre in the United Kingdom. Method Data were gathered by searching the histopathology database for cases between 2014 and 2019 containing the keywords ‘IDH Mutant’ AND ‘Astrocytoma’ or ‘Glioblastoma’ or ‘Oligodendroglioma’ in the report. Inclusion criteria: Biopsy/resection proven IDH mutant tumours in adults (age >17). A strict application of the T2-FLAIR mismatch sign was used when evaluating MRI. Native T2 signal was required to be homogenous or near homogenous, with hypointense signal on T2 weighted FLAIR except for a hyperintense peripheral rim. In addition, the T2-FLAIR mismatch sign was not applied to tumours showing any unequivocal contrast enhancement or macrocystic change. Results 66/185 cases were excluded for reasons of insufficient imaging, duplication, 1p19q partial deletion/unknown + ATRX wild type/unknown, IDH wild type/negative, Grade IV histology. 119 cases fit the inclusion criteria, all IDH positive. Group 1 comprised 49 (39%) 1p19q codeleted tumours, or oligodendrogliomas. ATRX was wild type (78%), unknown (18%), or mutated (