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Ischemic brain edema, the accumulation of fluid within the brain parenchyma following stroke, is a predictable consequence of both ischemic and hemorrhagic strokes. Its development is the result of injury to both brain parenchyma and the blood vessels supplying the parenchyma. Ischemic stroke produces both cytotoxic (intracellular) edema, which develops when cells are damaged, and vasogenic (extracellular) edema, which arises from injury to structures essential to blood–brain barrier integrity. An understanding of the distinction between cytotoxic and vasogenic edema is essential in preventing secondary brain injury, since the treatments for the two entities differ. The development of new brain imaging technologies has advanced our understanding of brain edema. Both computed tomography (CT) and magnetic resonance imaging (MRI) can detect edema. Specific MRI sequences such as diffusion-weighted imaging can distinguish cytotoxic and vasogenic subtypes, and thereby detect ischemic cell injury within minutes of the onset of symptoms.Brain edema causes neurologic deterioration predominantly through its mass effect, which leads to distortion of the intracranial contents and impairment of both regional and global cerebral blood flow (CBF). Edema may also cause local tissue dysfunction. Management of the intracranial hypertension and tissue shifts caused by ischemic brain swelling is based on the fundamental relationship between pressure, flow, and resistance. Interventions are directed at preserving CBF and preventing secondary brain injury. Strategies include reducing intracranial blood volume with hypocapnia, reducing brain volume with osmotic agents, reducing cerebral metabolism with hypothermia and barbiturates, reducing resistance with rheologic agents, increasing blood pressure with vasoconstrictors, and expanding the cranial vault with decompressive surgery. All individual therapies must be used as part of a structured approach that involves frequent serial neurologic assessments, quantitative measures of pressure, flow, and resistance, and prespecified protocols for intervention.