Tumors of the central nervous system constitute a vitally important chapter of neurologic medicine. Their importance derives from their great variety; the numerous neurologic symptoms caused by their size, location, and invasive qualities; the destruction and displacement of tissues in which they are situated; the elevation of intracranial pressure they cause; and, most of all, their lethality. The nature of practice for brain tumors is changing as a result of advances in anesthesiology, stereotactic and microneurosurgical techniques, focused radiation therapy, and the use of new chemotherapeutic agents. Moreover, our understanding of the genetic aspects of brain tumors is undergoing vast changes, which offer the prospect of new treatments.
For clinicians, several generalizations create a helpful framework for understanding these diseases. First, many types of tumor, both primary and secondary, occur in the cranial cavity and spinal canal but certain ones are much more frequent than others and are prone to occur in particular age groups. For example, secondary metastatic deposits are more common than primary brain tumors in adults and the opposite is true in children. Furthermore, certain cancers (breast, lung, melanoma, renal cell cancer) display a tendency to metastasize to nervous tissue and many others rarely do so. Second, some primary intracranial and spinal tumors, such as craniopharyngioma, meningioma, and schwannoma, have a disposition to grow in particular parts of the cranial cavity, thereby producing characteristic neurologic syndromes. Third, the presence of a state of immunosuppression such as AIDS or cancer chemotherapy, special inherited disorders such as neurofibromatosis, and exposure to radiation each predispose to the development of tumors of the nervous system. Fourth, the growth rates and invasiveness of tumors vary; some, like glioblastoma, are highly malignant, invasive, and rapidly progressive and others, like meningioma, are most often benign, slowly progressive, and compressive. These different qualities have substantial clinical implications, frequently providing the explanation of slowly or rapidly evolving clinical states as well as potential surgical cure and prognosis.
Furthermore, a special class of disorders results from the production of autoantibodies that are elaborated by systemic, nonneural tumors and these antibodies target cerebral and spinal neurons. These remote effects, referred to as paraneoplastic, often constitute the initial or only clinical manifestation of the underlying neoplasm. To this can be added the numerous direct and indirect effects on the nervous system of treatments for systemic cancer.
Comprehensive references on brain tumors and on the effects of cancer on the nervous system are the text edited by Kaye and Laws, and one by DeAngelis and Posner.
Incidence of CNS Tumors and Their Types
Currently, in each year there are an estimated 600,000 deaths from cancer in the United States. Of these, the number of patients who died of primary tumors of the brain seems comparatively small (approximately 20,000, half of them malignant gliomas), but in roughly another 130,000 patients ...