ABSTRACT
Introduction Once the genetic changes that lead to uncontrolled cellular reproduction have occurred, central nervous system (CNS) tumors must grow to a fairly large size (at least 1 cm) before causing neurologic symptoms. Most brain tumors grow both by increasing their core mass and by invading surrounding normal brain. In order to grow, a tumor requires nutrients that are supplied by the vasculature. After a tumor exceeds a few millimeters in size, it requires the production of new blood vessels (angiogenesis) to meet its metabolic demands. The newly formed blood vessels do not possess a normal blood-brain barrier and are thus a source of brain edema (see below), which contributes to the total tumor mass. The combined tumor mass and its edema not only cause neurologic dysfunction, but also raise interstitial fluid pressure, compromising blood flow and causing local hypoxia.1,2 The combined size of a tumor and its edema necessary to cause symptoms depends, in part, on the location of the lesion (for example, a 1 cm lesion in the brainstem may be symptomatic, but a 5 cm lesion in the frontal lobe may be asymptomatic) and, in part, on the nature of the symptom(s) (e.g. small lesions may cause seizures but it requires a large lesion to alter cognition or personality).
