Breakdown of the blood-brain barrier surrounding brain tumors and following infection or trauma disrupts fluid homeostasis and hydrostatic efflux of protein-rich fluid from the intravascular into the extracellular space occurs. Vasogenic edema is generated in the gray matter (more blood vessels) but spreads to the white matter where there are fewer cells and brain compliance is greater. Edema accumulation increases with fever, hypercarbia, hypoxia, and hypertension, and falls with hyperventilation, hypotension, and raised ICP but at the risk of cerebral ischemia. Studies utilizing CT and magnetic resonance imaging (MRI) have demonstrated pathways of edema formation and spread (Fig, 1). The initial pressure required to open channels is high, but thereafter bulk flow allows edema to spread with little pressure gradient. Edema resolves mainly by drainage into the ventricles or subarachnoid cerebrospinal fluid, down a pressure gradient between edematous subependymal regions and the cerebrospinal fluid in ventricles, and from uptake by glial cells. A small amount is reabsorbed into capillaries. The resolution of vasogenic brain edema is inversely related to ICP.
Fig. 1 Vasogenic edema in a patient with cerebral metastases. The CT scan shows a hypodense area around the tumor in the right hemisphere.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...