The patient went on to have a biopsy and sub-total resection.
All sections show a diffusely infiltrating glial neoplasm. The majority of the tumor is composed of cells with uniform small round nuclei surrounded by a clear perinuclear halo. These areas are associated with delicate branching capillary vasculature, macrocalcification, and focal microcystic architecture. Where the tumor diffusely infiltrates into the neocortex, there are prominent Sherer's secondary structures in the form of perineuronal, perivascular, and subpial aggregation of cells. In addition, there are focal nodular areas of marked hypercellularity where the cells have greater variation in nuclear size and shape and much more mitotic activity (up to 5 mitoses in a single high power field). Some of these cells have visible cytoplasm with either short delicate processes or micro-gemistocytic morphology. The hypercellular regions are also associated with and at least some endothelial proliferation and focal tumor necrosis. There are much larger confluent areas of acute necrosis associated with hemorrhage that more likely represents acute hemorrhagic infarction of part of the tumor. GFAP immunohistochemistry stains the minigemistocytes as well as reactive astrocytes in the cortex. MIB-1 labeling in significantly higher in the hypercellular nodules.
Right frontal lesion: anaplastic oligodendroglioma (WHO grade 3/4).