ABSTRACT
Neoplasms of the nervous system may be categorized into those that derive from cells of the brain, spinal cord, and peripheral nerve (primary tumors) and those that have metastasized to the central nervous system (CNS) from nonneural tissues. Metastatic tumors of the nervous system are more common than malignant brain and spinal cord tumors. Brain tumors account for 2% of all cancers but produce disproportionate morbidity and mortality when compared with other malignancies. Systemic malignancies may metastasize to the brain and cord parenchyma, leptomeninges, dura, and epidural space. Increased incidence may also be due to longer survival, as a result of improved systemic therapies with incomplete CNS penetration, creating sanctuary sites in the brain parenchyma and leptomeninges. According to the Monro–Kellie doctrine, brain parenchyma, blood, and cerebrospinal fluid occupy the fixed volume of the cranium. Increase in the volume of one compartment requires a compensatory decrease in the others.
