The patient went on to have a resection. 

Histology

Microscopic Description:

Sections show brain tissue infiltrated by a glial tumor that displays oligodendroglial features. Tumor infiltration into adjacent brain tissue is represented by subpial infiltration, focally prominent neuronal satellitosis and linear profiles of tumor cells. Perivascular infiltration by tumor cells is also observed. In the more cellular areas, the tumor cells display characteristic oligodendroglial features. Mitotic activity is increased in areas. Very focal vascular neogenesis is noted, represented by focal proliferation of endothelial cells. Tumor necrosis is not seen.

Final Diagnosis: anaplastic oligodendroglioma

Note: This case predates the 2016 revision WHO classification of CNS tumors, and thus molecular markers (IDH mutation and 1p19q co-deletion) are not available. As such, this tumor would now be classified as an oligodendroglioma NOS grade 3.