Furthermore, stroke is the major cause of disability in the adult population and has a staggering socioeconomic impact both directly in terms of health care costs and indirectly in lost income. A stroke may be caused by a diverse spectrum of disorders, such as a vascular occlusion, hypoxia, hypoglycemia, or bleeding into a tumor. 32-34 Most hemorrhagic strokes are caused by hypertensive arteriopathy, with other less common etiologies including amyloid angiopathy, aneurysms, vascular malformations, and moyamoya disease. The role of the radiologist is to confirm the clinical diagnosis and to more specifically identify the particular insult responsible for the stroke syndrome so that appropriate and timely therapy can be instituted. Ischemia is a physiological term indicating insufficient blood flow for normal cellular function.
Infarction is a pathological term denoting permanent tissue damage caused by ischemia.
There is often a dissociation between the events at the cellular level and the clinical status of the patient. Ischemia leads to alterations in the brain water content, even in its earliest stages. Because of MRI's inherent sensitivity to depict alterations in tissue-free water content, it can detect ischemic insult to the brain within 1 hour after onset. In addition, as a result of recent advances in MRI scanner hardware and software, the capability to image and measure molecular diffusion and capillary flow or perfusion has emerged, which is likely to significantly alter the future of neuroimaging. This chapter begins with an overview of the fundamental pathophysiological mechanisms of cerebral ischemia.