Neoplasms of the intracranial components of the central nervous system, including the cerebral hemispheres, basal ganglia, hypothalamus, thalamus, brain stem, and cerebellum; subdivided into primary (originating from brain tissue) and secondary (metastatic) forms; primary neoplasms are subdivided into benign and malignant forms; brain tumors may also be classified by age of onset, histologic type, or presenting location in the brain.