Stroke and brain parenchyma radiology

Stroke and Brain Parenchyma Nima Aghaebrahim August 28, 2008 Stroke  Third leading cause of death and leading cause of disability in the U.S  Incidence: 700,000 per year and increasing  about one stroke every minute  Every 3.3 minutes, someone dies of a stroke  Goal of imaging:  Establish diagnosis fast  Obtain accurate information regarding intracranial vasculature and brain perfusion  Appropriate therapy Goals of Acute Stroke Imaging   Ps Parenchyma:   Pipes:    Assess extracranial circulation (carotid and vertebral arteries of the neck) Assess intracranial circulation for evidence of intravascular thrombus Perfusion:   Assess early sign of acute stroke, rule out hemorrhage (unenhanced CT) Assess Cerebral blood volume, cerebral blood flow, and mean transit time Penumbra:  assess tissue at risk of dying if ischemia continues without recanalization of intravaslular thrombus It is all about the Penumbra!      When a cerebral artery is occluded, a core of brain tissue dies rapidly (irreversible) Surrounding this infarct core is an area of brain that is hypoperfused but does not die quickly, because of collateral blood flow, This surrounding area is penumbra (salvageable) Its fate depend on the reperfusion of the ischemic brain Will also die unless early recanalization is present  Thrombolysis via tPA, thrombus removal, etc Imaging options  Unenhanced  Not  T1 CT: rule out hemorrhage very good to detect ischemia or T2 weighted MRI  Good for detecting ischemia  Cannot differentiate between acute versus chronic ischemia  So we have… Diffusion-weighted MR  More sensitive for detection of hyperacutre ischemia  becomes abnormal within 30 minutes  Distinguish b/w old and new stroke  New stroke: bright on DWI  Old stroke: Low SI on DWI  It detects irreversible infarcted tissue Physiology  Ischemia  shortage of metabolites  Na+/K+ channel failure in the cell  Cause cytotoxic edema: shift of water into intracellular compartment  Leads to a narrowing of the extracellular matrix  Restricted diffusion of water within the cell  Increase signal which can be measured with DWI MRI OLD –VS- NEW ISCHEMIC INFARCT T1 T2 DIFFUSION Perfusion-Weighted imaging  Allows the measurement of capillary perfusion of the brain  Uses a MR contrast agent  The contrast bolus passage causes a nonlinear signal decrease in proportion to the perfusion cerebral blood volume  Meaning, it can identify areas of hypoperfusion, the reversible ischemia, as well (unlike DWI) Comparison of PWI and DWI  DWI  irreversibly damaged infarct  PWI  reflects the complete area of hypoperfusion  The volume difference between these two, the PWI/DWI mismatch would be the PENUMBRA!  If there is no difference in PWI and DWI, no penumbra is present Significance of PWI/DWI mismatch  IV thrombolytic treatment is not typically administered to patients with acute stroke beyond 3-hrs period  Risk of hemorrhage  However, recent studies have shown that IV thrombolytic therapy may benefit patients who are carefully selected according to PWI/DWI mismatch, beyond 3-hrs window (a) Diffusionweighted MR image shows an area of mildly increased signal intensity in the right parietal lobe (arrows) The ADC values in this region were decreased (b) Perfusion-weighted MR image shows a larger area with increased time to peak enhancement (arrows) in the right cerebral hemisphere The mismatch between the perfusion and diffusion images is indicative of a large penumbra Acute stroke in a 67-year-old woman with acute left hemiplegia hours after carotid endarterectomy CT PERFUSION Iodine Injection  CT angiography (CTA) and Perfusion CT (PCT) also provide information regarding vessel patency and the hemodynamic repercussions of a possible vessel occlusion  More widely available  Lower cost The Future   More effective selection of patient for thrombolytic therapy  PWI/DWI mismatch rather than time of onset as sole determinant of selection MR permeability imaging: based on dynamic contrastenhanced imaging  Allows quantization of defects in the blood-brain barrier, who have increased risk of hemorrhagic transformation with thrombolytic therapy Conclusion  Current imaging techniques can be used to identify hyperacutre stroke and guide therapy  PWI/DWI mismatch would be a good tool to identify a target group who would benefit from early reperfusion  Both CT and MR imaging are useful for the comprehensive evaluation of acute stroke Questions? Thank you .. .Stroke  Third leading cause of death and leading cause of disability in the U.S  Incidence: 700,000 per year and increasing  about one stroke every minute  Every... dies of a stroke  Goal of imaging:  Establish diagnosis fast  Obtain accurate information regarding intracranial vasculature and brain perfusion  Appropriate therapy Goals of Acute Stroke Imaging... hyperacutre ischemia  becomes abnormal within 30 minutes  Distinguish b/w old and new stroke  New stroke: bright on DWI  Old stroke: Low SI on DWI  It detects irreversible infarcted tissue Physiology