Diffuse astrocytoma IDH-mutant

Case contributed by RMH Neuropathology
Diagnosis certain


Aortic valve replacement on warfarin. One episode of seizure/syncope with the loss of consciousness +/- head strike. No focal neurology.

Patient Data

Age: 50 years
Gender: Male

CT Brain


There is a well-defined hypodense lesion centered on the right insular cortex extending into the right frontal and temporal lobes. It does not demonstrate any ring enhancement post contrast administration nor is there any identifiable contrast enhancing component elsewhere in the lesion. The lesion exerts mass effect, with partial effacement of the right lateral ventricle and midline shift of 2 mm to the left as measured at the septum pellucidum. A small peripheral hypodense cortical component extends into the inferior aspect of the right frontal lobe. No vascular malformation associated with the lesion.

No acute intracranial hemorrhage or acute cortical infarct. No acute calvarial fracture. The mastoid air cells and paranasal sinuses are aerated.

Impression: Right insular/frontal/temporal non-enhancing hypodense lesion exerting mild local mass-effect. Appearances favor low-grade tumor and MRI is suggested to further characterize.

MRI Brain


There is a large intra-axial mass in the right insula extending anteriorly into the frontal operculum and inferiorly into the temporal lobe close to the amygdala. A small component extends inferolaterally to involve the right lateral orbital gyrus. This is joined to the main bulk of tumor by a small area of abnormal FLAIR hyperintense cortex via the inferior frontal gyrus.

There is extensive involvement of grey matter with gyral expansion in the insula and frontal lobe. The tumor is well circumscribed, brightly T2 and FLAIR hyperintense with a few small foci of FLAIR suppression.

There is very subtle wispy contrast enhancement in the mass.

No abnormal elevation of relative cerebral blood volume (CBV). MR spectroscopy is non-contributory.

No abnormal susceptibility related signal loss. No abnormal diffusion restriction.

Tumor exerts mass effect on the superior temporal gyrus and causes partial effacement of the right sylvian fissure and 2.5 cm of midline shift to the left.

Conclusion: Large intra-axial tumor centered in right insula. Appearance most in keeping with of low-grade glioma. Foci of FLAIR suppression, wispy contrast enhancement, and cortical involvement suggest protoplasmic or oligodendroglial components.


MICROSCOPIC DESCRIPTION: Sections show a moderately cellular tumor composed of glial cells with round-to-oval nuclei, smooth chromatin and inconspicuous nucleoli. No necrosis or microvascular proliferation is seen. No mitoses are identified.Immunohistochemistry results show tumor cells stain:

  • GFAP Positive
  • Nestin Positive (low)
  • IDH-1 R132H Positive (mutated)
  • ATRX Negative (mutated)
  • MGMT Negative (likely methylated)
  • NogoA Positive (focal)
  • p53 Positive
  • p16 CDKN2A Positive

Topoisomerase labeling index: Approximately <5%.

The features are of low-grade diffuse astrocytoma, WHO grade II.

DIAGNOSIS: diffuse astrocytoma, WHO grade II.



FISH for chromosome 1p/19q deletion.



Case Discussion

This case demonstrates a confirmed case of a low-grade diffuse astrocytoma, which is a well-differentiated but infiltrating tumor. 

This tumor is: 

  • IDH-1 positive (mutated) = better prognosis
  • 1p19q not codeleted


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