The patient went on to have a craniotomy and debulking of the mass.
The sections show a glial neoplasm that diffusely infiltrates brain tissue. The tumour is remarkable for the variety of histologic appearances. Many areas show definite oligodendroglioma differentiation with uniform round cells surrounded by perinuclear halos associated with capillary proliferation and focal microcalcification. In focal areas, this portion of the tumour becomes more cellular and shows a greater degree of nuclear pleomorphism and rare mitotic figures. Other areas show definite astrocytic differentiation, including both gemistocytic and pilocytic morphology. Rare mitotic figures are present in the gemistocytic areas. Finally, areas composed of cells with relatively uniform small round nuclei and short delicate processes associated with prominent microcystic architecture could either represent oligodendroglioma or protoplasmic astrocytoma. Vascular changes include hyalinized vessels and focal aggregates of dilated capillary vessels resembling telangiectasia. No endothelial proliferation or necrosis is identified. Large neurons are scattered throughout the tumour, however, these appear to represent entrapped normal cortical neurons.
This tumour shows distinct areas of both oligodendroglioma and astrocytoma (oligoastrocytoma). Although much of the tumour appears to be low grade, the presence of some mitotic activity in the more poorly differentiated portions of the oligodendroglioma as well as the gemistocytic areas of astrocytoma are worrisome and suggest this tumour should be graded as III.