(A) “Malignant” oligodendroglioma characterized by large, well-circumscribed lesions spread over multiple areas of the brain, with necrosis and hemorrhage. (B) Atypical capillary endothelial hyperplasia characteristic of malignant oligodendrogliomas. (C) “Benign” oligoden-droglioma characterized by a small, well-circumscribed lesion that is confined to one major area of the brain. (D) The benign oligodendroglioma often shows a “honeycomb” or “fried egg” cell pattern. (E) Astrocytoma with cells that have protoplasmic or fibrillary differentiation and prominent round or oval nuclei. (F) Necrosis with pseudopalisading is one characteristic feature of astrocytomas. (G) The mixed glioma of the mouse can show both proliferative astrocytoma and oligodendroglioma-like features. (H) A malignant pinealoma often expands by invasion into the adjacent brain tissue and is highly cellular, rich in mitotic figures, and pleomorphic.