Astrocytoma, IDH-mutant - grade 3

Case contributed by Frank Gaillard
Diagnosis certain



Patient Data

Age: 35 Years

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 edema. Whilst the distinction between intra and extra-axial location is somewhat difficult, a cortically-based tumor arising from the middle frontal gyrus is strongly favored. 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 favored to represent a low-grade cortically-based tumor such as a DNET, diffuse astrocytoma or oligoastrocytoma.

Case Discussion

The patient went on to have surgery.


Paraffin sections show a moderately hypercellular glial tumor 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 labeling index: Approximately 5%.

COMMENT: This glial tumor has mixed morphological features. Positive immunostaining for p53 and weak/negative staining for ATRX favor astrocytoma. However, many tumor cells show strong positive staining for NogoA indicating an oligodendroglial component. FISH for chromosome 1p/19q deletion is thus indicated. 

1p19q co-deletion:



astrocytoma IDH-mutant (WHO CNS grade 3)


This case is unusual and presumably represents a low-grade astrocytoma IDH-mutant which is in the process of becoming more aggressive.

Note, the presence of microvascular proliferation strictly speaking is sufficient to designate this tumor a WHO grade 4, however as the majority of this tumor does not demonstrate this feature, the absence of necrosis, preservation of CDKN2A and low-grade MRI appearances resulted in it being designated a grade 3 tumor by the pathologists. 

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