A relatively slow-growing glioma that is derived from oligodendrocytes and tends to occur in the cerebral hemispheres, thalamus, or lateral ventricle. They may present at any age, but are most frequent in the third to fifth decades, with an earlier incidence peak in the first decade. Histologically, these tumors are encapsulated, relatively avascular, and tend to form cysts and microcalcifications. Neoplastic cells tend to have small round nuclei surrounded by unstained nuclei. The tumors may vary from well-differentiated to highly anaplastic forms. (From DeVita et al., Cancer: Principles and Practice of Oncology, 5th ed, p2052; Adams et al., Principles of Neurology, 6th ed, p655).