WHO 2016 Classification of Infiltrating Gliomas

Diagnosis	Common Mutations	Additional Characteristics
Astrocytoma
Diffuse astrocytoma, IDH-mutant (WHO grade II)	IDH1/IDH2 ATRX TP53 TERT promoter EGFR amplification +7/−10 PTEN mutation/loss H3.3 p.K27M	Usually younger patients (40–50 years old); present as lower gliomas; most glioblastomas in this group are secondary
Anaplastic astrocytoma, IDH-mutant (WHO grade III)
Glioblastoma, IDH-mutant (WHO grade IV)
Diffuse astrocytoma, IDH-wildtype (WHO grade II)		Usually older patients (>55 years old); present as high-grade gliomas; most glioblastomas in this group are primary
Anaplastic astrocytoma, IDH-wildtype (WHO grade III)
Glioblastoma, IDH-wildtype (WHO grade IV)
Diffuse midline glioma, H3 -K27M-mutant		Midline location, infiltrating on histology, H3.3 p.K27M mutation
Oligodendroglioma
Oligodendroglioma, IDH-mutant, 1p/19q codeleted (WHO grade II)	IDH1/IDH2 1p/19q codeletion	ATRX is wild-type (ATRX mutations are mutually exclusive with 1p/19q codeletion), strong correlation with perinuclear clearing histology
Anaplastic oligodendroglioma, IDH-mutant, 1p/19q codeleted (WHO grade III)

Low Grade Glioma

1° goal in initial Tx of LGG is max. safe resection → assoc. w/ prolonged survival, sz pPx, ↓ risk of transformation;
Qx for suspected LGGs challenges:
- GTR is difficult d/t the diffusely infiltrative growth pattern of LGG → difficult to id the exact tumor borders; ∴ image guidance w/ FLAIR is crucial.
- Histopathological undergrading is common w/ Bx, as LGG often exhibits focal areas of malignant transformation (anaplastic foci). To avoid this and reduce subsequent treatment failure, the surgical goal is to perform precise tissue sampling from a potential anaplastic focus.
- "Eloquent" localization → awake Qx ± functional mapping