Oligoastrocytoma NOS (multifocal)
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MRI demonstrates a diffuse and enhancing mass which involves the left side of the pons as well as the cerebral peduncle and left thalamus. Appearances are consistent with a glioma.
The patient went on to have a biopsy.
Sections show fragments of a high-grade glial neoplasm with an oligodendroglial component, characterised by cells with anaplastic round nuclei and variable perinuclear halo formation. Neuronal satellitosis is evident in some of the fragments. Also identified is a population of tumour cells with more elongated nuclear profiles associated with hyperchromasia and significant pleomorphism. The latter cells are consistent with neoplastic astrocytes. Mitotic figures are identified. Single cell apoptosis is identified focally but no areas of necrosis are seen. There are prominent endothelial cells but no definite microvascular proliferation is seen.
Immunohistochemistry for glial acidic protein (GFAP) shows that the tumour contains GFAP-positive cells, some with anaplastic elongated nuclei, but many of the cells with round nuclei are negative for GFAP. Nuclei are frequently positive for the cell proliferation marker MIB1.
The biopsy findings are those of high-grade oligoastrocytoma with many cells showing an oligodendroglial morphologic phenotype and probably less numerous astrocytes. Given the lack of necrosis, the grading of this oligoastrocytoma in this stereotactic biopsy would be Grade 3 by the most recent WHO criteria. However, since a stereotactic biopsy is a small sample, it is possible that other areas of the tumour may be of a different grade and have a different relative proportion of the two glial cell lineages.
NOTE: This case predates the 2016 WHO classification of CNS tumour 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 recognised 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.