Diffuse astrocytoma NOS

Case contributed by Dr Henry Knipe

Presentation

High-speed motor vehicle accident.

Patient Data

Age: 30 years
Gender: Male
CT

There is a large low-density intra-axial mass centred in the left frontal lobe, crossing the midline via the corpus callosum. Marked compression of the frontal horns of the lateral ventricles, with up to 10 mm of rightward subfalcine midline shift. No enhancement is appreciated.

MRI

Very large left frontal mass measuring approximately 9.1 x 7.0 x 6.3 cm. It has high T2 signal with loss of grey-white differentiation and gyral expansion. It appears very heterogeneous on FLAIR, studded with numerous small cystic spaces, and has mildly heterogeneous low T1 signal. It crosses the midline via an expanded corpus callosal genu. There is a small amount of surrounding high FLAIR signal. No diffusion restriction. No definite enhancement. At the inferolateral aspect of the mass is some intrinsic T1 signal, likely haemorrhage with corresponding susceptibility artefact and precontrast hyperdensity on the CT. No increased CBV. MRS demonstrated low NAA and reversal of the normal choline-creatine ratio.

The patient proceeded to surgery.

Histopathology

MICROSCOPIC DESCRIPTION: Paraffin sections show a moderately hypercellular glial tumour. The majority of tumour cells have oligodendroglial morphological features with moderately pleomorphic round and oval hyperchromatic nuclei and a paucity of delicate processes. Moderate numbers of mini-gemistocytes and gliofibrillary oligodendroglial cells are also noted. There is prominent microcyst formation. Scattered mitotic figures are noted (2 in 20 HPF). There is no microvascular proliferation and no necrosis is identified. The features are of a diffuse glioma favouring oligodendroglioma (WHO Grade II).

IMMUNOHISTOCHEMISTRY:

  • GFAP positive
  • Nestin positive (low) 
  • Nogo A negative
  • IDH-1 R132H negative (not mutated)
  • ATRX negative (mutated)
  • p53 positive
  • MGMT negative (likely methylated)
  • p16 CDKN2A positive
  • Topoisomerase labelling index: Approximately 2%.

FINAL DIAGNOSIS: probable IDH wild type diffuse astrocytoma (WHO Grade II).

Note: The diagnosis of astrocytoma is very likely but according to the current WHO classification of CNS tumours (2016) it has actually not yet been established in this case as the IDH wild-type status has only been inferred with a negative IDH1 R132H immunohistochemistry. Although it is likely to reflect true IDH wild-type status, it is possible that this is a non-R132H IDH1 mutation or an IDH2 mutation (which account for ~20% of all IDH mutations). In younger patients, IDH sequencing is therefore recommended to prove that no IDH mutation is present.

Additionally, as the histological morphology suggests that this is an oligodendroglioma, 1p19q codeletion status would also need to be established (if IDH sequencing showed a mutation).  

Having said that the absence of IDH1-R132H and mutated ATRX are highly suggestive of 1p19q being intact, and thus not an oligodendroglioma under the current classification. 

Overall this would be therefore classified as a diffuse astrocytoma NOS

Case Discussion

IDH-1 negative/nonmutated is known as IDH wild-type, and carries a worse prognosis than IDH-mutated diffuse gliomas. 

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Case information

rID: 53616
Case created: 27th May 2017
Last edited: 7th Jun 2017
Inclusion in quiz mode: Included

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