Part of this increase in tumors incidence might be attributed to improvement in imaging technology, yet further studies are required to look for other causes especially with the increasing incidence of CNS tumors at younger ages also. CNS tumors represent the second most frequent malignancy in children under the age of 15 years. Children with brain tumors have a better prognosis than adults, in part, because children rarely develop the highly malignant tumors of adults, glioblastoma. Also, low grade gliomas tend to remain histologically low grade and, in general, gliomas in children do not demonstrate the same molecular genetic changes identified in adults. Although brain tumors rarely metastasize outside the CNS with the exception of medulloblastoma and malignant meningioma, yet in general they have a poor prognosis and a grim outcome.
Several features serve to distinguish primary brain tumors both clinically and biologically.
First, because of their location inside the bony confines of the skull or spinal column, these tumors may cause symptoms and morbidity by direct invasion or compression of normal tissue or by increasing intracranial or intraspinal pressure. The focal organization of brain function, together with poor ability to regenerate and the obvious difficulties of radical surgical excisions, means that these tumors are associated with high morbidity and mortality. These gliomas are prone to infiltrative invasion of normal brain tissue that renders complete surgical excision of such tumors a rare occasion. Also, these tumors tend to progress from a well differentiated to higher grade, poorly differentiated neoplasms with a more aggressive behavior. Aside from tumors of neuronal and central glial origin, several other tumor types in the CNS deserve mention.