Management of Patients with Ischemic Stroke

In a case with embolic occlusion of cerebral artery, residual cerebral blood flow (CBF) in symptomatic ischemic region is distributed heterogeneously and cerebral infarction is developed gradually from ischemic core to penumbra. Ischemic core is defined as a region with irreversible tissue damage due to fairly poor collateral circulation, and ischemic penumbra is defined as a region with preservation of tissue reversibility in a certain time. Reversibility of ischemic penumbra is also depending on both residual CBF and time from stroke onset, and the existence of ischemic penumbra is essential for thrombolytic therapy. Ischemic penumbra is thought to be the first therapeutic target in management of patients with acute cerebral ischemia. Using 133Xe SPECT imaging, penumbral flow is estimated as 15-30 m1/100g/min within 3 hours from stroke onset and 20-30 m1/100g/min during 3-6 hours from stroke onset. Ischemic penumbra could be diagnosed accurately by both negative findings on DWI and critical flow level in brain perfusion SPECT or other perfusion image. Hemodynamic cerebral ischemia could be stratified into Stage I and Stage II (Misery perfusion). According to vasodilatory and metabolic compensation toward reduction of cerebral perfusion pressure, Stage I ischemia is defined as both preservation of resting CBF and reduction of vascular reserve (VR). Stage II ischemia is defined as reduction of resting CBF associated with loss of VR. The vasodilatory response to acetazolamide provides an effective parameter of VR: (acetazolamide-activated CBF / resting CBF ? 1) X 100%. Stage II ischemia is quantitatively defined as both CBF less than 80% of normal mean CBF and VR less than 10%. Stratification of hemodynamic cerebral ischemia could be important to determine future risk of stroke. Stage II ischemia is thought to be the second therapeutic target in management of patients with hemodynamic cerebral ischemia. The characteristics and kinetics of brain perfusion radiotracers should be considered in quantitative stratification of hemodynamic cerebral ischemia using brain perfusion SPECT