Anaplastic astrocytoma IDH mutant
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A right frontal lesion is present demonstrating mass-effect on the inferior aspect of the superior frontal gyrus. The lesion is T1 hypointense and T2 hyperintense with incomplete suppression, occasional areas of central irregular low signal and a peripheral high rim on FLAIR. The lesion demonstrates no enhancement, is well defined and there is no surrounding oedema. Whilst the distinction between intra and extra-axial location is somewhat difficult, a cortically-based tumour arising from the middle frontal gyrus is strongly favoured. No significant diffusion restriction. No intrinsic or surrounding gradient susceptibility cerebral blood volume (CBV) is not elevated and spectroscopy is equivocal. No additional lesions identified.
Conclusion: The lesion is favoured to represent a low-grade cortically-based tumour such as a DNET, diffuse astrocytoma or oligoastrocytoma.
The patient went on to have surgery.
MICROSCOPIC DESCRIPTION: Paraffin sections show a moderately hypercellular glial tumour with mixed morphology. Both oligodendroglial and astrocytic morphology is discernible and there is a prominent population of reactive astrocytes. Scattered mitotic figures are identified (3/20 HPF). A focus of microvascular proliferation with multi-layering of atypical cells around vessel lumens is demonstrated. No necrosis is identified.
- GFAP positive in astrocytic cells, negative in oligodendroglial cells.
- NogoA positive in oligodendroglial cells
- Nestin positive (low)
- IDH-1 R132H positive (mutated)
- ATRX negative (mutated)
- MGMT negative (likely methylated)
- p53 positive
- p16 CDKN2A positive
- Topoisomerase labelling index: Approximately 5%.
COMMENT: This glial tumour has mixed morphological features. Positive immunostaining for p53 and weak/negative staining for ATRX favour astrocytoma. However, many tumour cells show strong positive staining for NogoA indicating an oligodendroglial component. FISH for chromosome 1p/19q deletion is thus indicated.
SUPPLEMENTARY REPORT - 1p19q co-deletion:
- 1p/19q FISH 1p36 NO DELETION DETECTED
- 19q13.3 DELETION DETECTED
Right frontal tumour: IDH-1 mutated/ATRX mutated anaplastic astrocytoma (WHO Grade III)
This case is tricky and represents a low-grade glioma (IDH mt) which is in the process of becoming far more aggressive. Microvascular proliferation strictly speaking is grounds for calling this tumour a WHO grade IV (GBM). As the majority of this tumour does not demonstrate this feature, absence of necrosis and low-grade MRI appearances resulted in it being designated a grade III.