Fig. 2

Typical histologic features of infiltrating gliomas. In diffuse astrocytomas (a), cellularity is increased due to infiltrating neoplastic astrocytes with irregular, hyperchromatic nuclei and scant associated cytoplasm. Immunohistochemistry for IDH1 R132H mutant protein (A, inset) can be helpful when infiltrating cells are sparse or rare. b Anaplastic astrocytoma is distinguished by mitotic activity (black arrow). Note the infiltrating tumor cells around a non-neoplastic neuron (white arrowhead). c Palisading necrosis (left) and endothelial proliferation (upper right) are histologic features of glioblastoma, though neither feature is absolutely specific. d WHO grade II oligodendroglioma with uniform, rounded nuclei and perinuclear clearing, the latter feature being an artifact of formalin fixation. Infiltrative growth is demonstrated by entrapped non-neoplastic neurons (white arrowheads). e Oligodendrogliomas with high cellularity, cytologic atypia, significant mitotic activity (black arrows) generally defined as 6 or more mitoses per 10 high-power fields, and vascular proliferation qualify for anaplastic oligodendroglioma, WHO grade III. Necrosis often accompanies vascular proliferation and mitotic activity, but is not required. f Gemistocytic astrocytoma appears as cells with abundant, glassy, eosinophilic cytoplasm, and frequently is associated with perivascular inflammatory infiltrates. This astrocytoma subtype has a propensity toward rapid malignant progression