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Diffuse astrocytoma, IDH-mutant

Case contributed by Derek Smith

Presentation

First seizure. MRI work up.

Patient Data

Age: 35 years
Gender: Male

Right frontal signal abnormality involving cortex and white matter, with mild expansion. There is minor midline shift anteriorly, but no abnormality of the displaced left frontal lobe. There is T2-FLAIR mismatch. Diffusion is predominantly facilitated. No abnormal enhancement.

Opinion: Features compatible with a lower grade glial tumor. Astrocytoma favored with T2-FLAIR mismatch and subcortical center, but oligodendroglioma also possible given position / age.

The lesion was debulked, with trace residual tissue at the deep margin.

PATHOLOGY: Extensively infiltrated sample with astrocytic glioma. Mild to moderate nuclear pleomorphism. No microvascular involvement. Inconspicuous mitotic activity. No calcification. GFAP strongly expressed, with IDH1 mutation. ATRX expression is lost. Low MIB1. No evidence of 1p19q co-deletion.
--> Diffuse astrocytoma, WHO grade 2.

The case was followed up for a number of years with frequent clinical and imaging review. There was progression of non-enhancing tumor with radiotherapy delivered in year 3 with good response. 

6Y after initial debulking

mri

At the deep resection margin there is now a approximately 20 mm solid enhancing nodule. This appears cellular with low ADC values. There has also been progressive surrounding FLAIR abnormality and while some of this will be treatment effects (scattered microbleeds on SWI noted), some is also considered likely to be nonenhanicng tumor infiltration.

The patient proceeded to repeat surgery.

PATHOLOGY: Diffusely infiltrating pleomorphic astrocytic tumor with mucinous stroma. Mitotic figures are easily identified. Intrinsic necrosis and microvascular proliferation are seen. Some vessel walls are hyalinised consistent with previous radiotherapy. GFAP and IDH1 are expressed (mutant). ATRX is lost (mutant), with associated upregulation of P53. High MIB1 index proliferation. No expression of H3K27M. No evidence of 1p19q co-deletion. MGMT is methylated (34%).
--> diffuse astrocytoma, IDH1 mutated, WHO CNS grade 4

Case Discussion

This case shows a progression over 6 years from a grade 2 to a grade 4 lesion, with an enhancing focus with necrosis and microvascular proliferation confirmed on pathology. Prior to the 2021 WHO CNS 5th edition update, this would have been termed a glioblastoma IDH mutant (or in even older terminology a secondary glioblastoma), but now due to this mutation it should be termed a diffuse astrocytoma, IDH mutant, WHO CNS grade 4.

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