Oligoastrocytoma NOS

Case contributed by Bruno Di Muzio
Diagnosis certain

Presentation

Not available.

Patient Data

Age: 30 years
Gender: Male
ct

CT brain shows a right frontal hypodense subcortical area that does not enhance after contrast administration. No acute intracranial hemorrhage. Cortical volume is age-appropriate. No hydrocephalus. The basal cisterns are unremarkable. The paranasal sinuses and mastoid air cells are clear. No suspicious osseous lesion.

mri

MRI brain shows a right precentral frontal superior gyrus lesion characterized by two small subcortical T2 hyperintense foci surrounded by FLAIR hyperintensities and without contrast enhancement. The remaining brain parenchyma is unremarkable. 

mri

MRI brain demonstrates again the precentral lesion slightly increased compared to the previous MRI exam and now showing linear enhancement in its borders. The remaining brain parenchyma is unremarkable. 

MICROSCOPIC DESCRIPTION: Sections show white matter invaded by a diffuse population of atypical glial cells with enlarged, round nuclei many of which are surrounded by clear haloes. There is a network of fine capillaries in the background and some small calcified foci. Scattered mitotic figures are identified (2/10HPF). No endothelial cell hyperplasia or necrosis is seen.

IMMUNOHISTOCHEMISTRY:

  • GFAP positive
  • Nogo A positive
  • IDH-1 positive
  • MGMT negative (likely methylated)
  • p53 positive in a small number of tumor cells
  • Topoisomerase labeling index: Approximately 10%. 

DIAGNOSIS: Right precentral gyrus lesion: Oligoastrocytoma (NOS) (WHO Grade II)

Case Discussion

Both CT and MRI illustrate features of a low-grade glioma tumor in the right precentral frontal lobe.

Oligoastrocytomas are infiltrating gliomas composed of a mixture of two distinct neoplastic cell types resembling the tumor cells in oligodendroglioma and astrocytoma. They are a WHO grade II tumors and preferentially develop in adults between 35-45 years of age. 

NOTE: This case predates the 2016 WHO classification of CNS tumor revision. As no 1p19q co-deletion status is available a formal diagnosis cannot be reached and the NOS is therefore used (not otherwise specified) - which is recognized in the current classification for cases where molecular information is unavailable. It should also be noted, that under the new classification both an astrocytic and oligodendroglial component needs to be identified, each with its own molecular markers. True oligoastrocytomas are therefore going to be rare, and this case would most likely be classified as either an astrocytoma or an oligodendroglioma. 

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