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Anaplastic astrocytoma, IDH-mutant is a CNS WHO Grade 3 infiltrative astrocytic tumor, defined by:

Histologic features of high-grade astrocytoma, and
Presence of an IDH1 or IDH2 mutation. </aside>

It is more aggressive than diffuse (grade 2) astrocytoma but distinct from glioblastoma due to absence of microvascular proliferation or necrosis.

Etiopathogenesis

Arises from lower-grade diffuse astrocytomas (IDH-mutant)
Key mutations:
- IDH1/IDH2 mutation (required)
- TP53 mutation (common)
- ATRX loss
No 1p/19q co-deletion (excludes oligodendroglioma)
CDKN2A/B homozygous deletion may suggest worse prognosis or grade 4 behavior

Clinical Features

Feature	Description
Age	Typically 30–50 years
Symptoms	Seizures, headache, focal neurologic deficits, cognitive decline
Common sites	Frontal and temporal lobes

Radiology

MRI Sequence	Imaging Features
T1WI	Hypointense or isointense mass
T2/FLAIR	Hyperintense, infiltrative lesion; more extensive than seen on T1
Contrast-enhanced T1	Variable enhancement (patchy or nodular), but not ring-enhancing like GBM
DWI/ADC	Mild-to-moderate diffusion restriction (reflects increased cellularity)
Perfusion MRI	rCBV is elevated, less than glioblastoma but more than grade 2
MR Spectroscopy	↑Choline, ↓NAA, possible lactate peak
SWI	May show microhemorrhage, calcification if aggressive

![Targeting biopsy for a non-enhancing tumour. Conventional MRI: a, b Post-contrast T1W and T2W sequences demonstrate a large non-enhancing space occupying mass lesion without significant oedema. Multiparametric MRI: c, d Heterogeneous ADC and rCBV values throughout the lesion. e Multi-voxel MRS clearly shows focal area of very high Cho/Cr (3.1) and very small lactate peak. f Targeted biopsy taken from the area of highest choline peak (arrow). Histopathology shows anaplastic astrocytoma with moderately atypical astrocytic cells in a fibrillary background with a few abnormal mitoses (WHO grade III).

Sawlani, V., Patel, M.D., Davies, N. et al. Multiparametric MRI: practical approach and pictorial review of a useful tool in the evaluation of brain tumours and tumour-like lesions. Insights Imaging 11, 84 (2020). https://doi.org/10.1186/s13244-020-00888-1](attachment:2a5a6bde-d535-44d6-a857-c76bcac46654:13244_2020_888_Fig5_HTML.webp)

Targeting biopsy for a non-enhancing tumour. Conventional MRI: a, b Post-contrast T1W and T2W sequences demonstrate a large non-enhancing space occupying mass lesion without significant oedema. Multiparametric MRI: c, d Heterogeneous ADC and rCBV values throughout the lesion. e Multi-voxel MRS clearly shows focal area of very high Cho/Cr (3.1) and very small lactate peak. f Targeted biopsy taken from the area of highest choline peak (arrow). Histopathology shows anaplastic astrocytoma with moderately atypical astrocytic cells in a fibrillary background with a few abnormal mitoses (WHO grade III).

Differentials

Key differences vs related tumors:

Feature	Diffuse astrocytoma	Anaplastic astrocytoma	Glioblastoma
WHO grade	Grade 2	Grade 3	Grade 3
Enhancement	Absent/minimal	Variable	Ring-enhancing with necrosis
Cellularity	Low	Moderate-high	Very high
DWI restriction	No	Mild	Prominent
Necrosis	Absent	Absent	Present
Prognosis	8–10 years	3–5 years	~15 months

Other differentials: