Imaging cannot give the molecular diagnosis but can predict it: the T2–FLAIR mismatch sign suggests IDH-mutant astrocytoma, calcification and frontal cortical location suggest oligodendroglioma, necrosis and a thick enhancing rim suggest glioblastoma — and the report maps eloquent cortex for surgery.
Orient first
- CNS5 classifies adult diffuse gliomas by molecular markers: astrocytoma IDH-mutant, oligodendroglioma IDH-mutant and 1p/19q-codeleted, and glioblastoma IDH-wildtype (verify the edition).
- An IDH-wildtype astrocytoma with TERT promoter mutation, EGFR amplification or +7/−10 is glioblastoma even without necrosis — so a non-enhancing tumour can be grade 4.
- Enhancement is not the tumour border: infiltrative tumour extends into the FLAIR abnormality.
Acquire the study
- MRI brain: 3D T1 pre- and post-gadolinium, axial T2, 3D FLAIR, DWI/ADC, SWI; perfusion (DSC rCBV) and MR spectroscopy where available.
The manoeuvre
- T2 and FLAIR: extent of the non-enhancing tumour; T2–FLAIR mismatch (homogeneously T2-bright, FLAIR-dark centre with a bright rim) suggests IDH-mutant 1p/19q-intact astrocytoma.
- Post-gadolinium 3D T1: enhancing component, necrosis (non-enhancing centre with thick irregular rim), measure in three planes (RANO baseline).
- SWI: calcification (favours oligodendroglioma) and haemorrhage.
- DWI/ADC: low ADC in solid parts = high cellularity.
- DSC perfusion: raised rCBV in the non-enhancing tumour points to higher grade or target for biopsy.
- Mass effect: midline shift in mm, subfalcine and uncal herniation; relation to eloquent cortex and the corticospinal tract.
What confirms it
- An intra-axial infiltrative mass with imaging features in keeping with a glioma; histology and molecular testing give the integrated diagnosis.
What licenses you to exclude it
- A lesion with restricted diffusion and an incomplete ring open towards the cortex favours demyelination; a well-defined ring with a smooth inner wall and restricted centre favours abscess.
The classic misread
- Calling a non-enhancing tumour "low grade" — IDH-wildtype tumours can be glioblastoma without enhancement.
- Measuring only the enhancing rim and missing the infiltrative FLAIR component.