Several characteristics of brain tumors distinguish them from other types of tumors. Even the most malignant brain tumors rarely metastasize outside the nervous system.
• The location of a tumor often determines whether a neurological deficit occurs.
• The most common brain tumor, the astrocytoma, ranges from a low- to high-grade type (the grade of each
tumor is based on its microscopic features and determines type of treatment and prognosis).
• Even tumors regarded as slow growing or more benign can produce symptoms as severe and life-threatening as
malignant tumors. This is because they may occur in a vital area of the brain or because when they reach a
critical size there is no room for them to expand within the surrounding skull. This puts significant pressure on
key structures.
• The brain has no lymphatic blood vessels to remove the products of tumor dissolution, so the tumor may not
appear to shrink on CT or MRI scans even if treatment is successful.
• Treatment of a tumor can result in a new neurological deficit. A temporary or permanent loss of function can
occur after surgery and problems of brain swelling can occur during radiation treatments, for example.
• Unless a dramatic, early and sustained improvement occurs after therapy, it may be difficult for a long time to
determine the response to treatment. Treatments may themselves produce temporary neurological deterioration
