![]() ![]() Based on the total amount and speed that blood flows to different vascular territories of the brain this technique can assist in identifying a stroke and potential areas of reversible and salvageable brain tissue in the ischemic penumbra. During CT perfusion a rapid intravenous infusion of contrast is administered and sections of the brain are repeatedly imaged. 4 Rotation of these images can also assist stroke neurologist, interventional neuroradiologist and surgeons in planning operations and procedures.ĬT perfusion is more widely available than magnetic resonance imaging (MRI) and can be performed quickly on any standard helical CT scanner right after unenhanced CT. In addition to identifying stenotic and occluded blood vessels the CTA can provide images of aneurysms ( Figures 6 and and7) 7) and other vascular abnormalities such as arterio-venous malformation (AVM) and their feeding arteries and veins ( Figure 8). For example, when a carotid dissection is identified on the CTA, then more aggressive mechanical thrombolytic therapy would not be indicated. The identification of extracranial carotid arterial disease on the CTA and the visualization of the aortic arch might provide the cause of an ischemic event. Intra-arterial administration of thrombolytics or mechanical clot removal using catheter angiography might be beneficial in patients presenting later than three hours if a large and accessible thrombus is identified and it becomes the decision of the skilled interventional neuroradiologist or neurosurgeon to consider these patients for experimental therapy. When the CT angiogram reveals an occlusion of a major cerebral blood vessel within the three hour time limit, then the decision to administer intravenous tissue plasminogen activator (TPA, specifically alteplase) can be made with more confidence as the cause of the stroke is more accurately identified. CT angiograms that identify occluded blood vessels in the brain assist the neurologist and emergency physician in treatment decisions. The identification of areas of stenosis or occlusion of vessels allows for rapid and accurate diagnoses and decisions in the clinical arena. Coronal two-dimensional reconstruction from a computed tomography angiogram demonstrates transfalcine herniation (arrows) to the left due to large right sided intraparenchymal hemorrhage. Hypertensive intraparenchymal hematoma with subfalcine herniation. 4 This tool’s availability and speed make it very useful in the initial evaluation of suspected stroke patients. Noncontrast CT is also used in the evaluation of acute intracranial hemorrhage as it produces good contrast between the high attenuating (“bright”) clot and the low attenuating (“dark”) cerebrospinal fluid (CSF). Chronic strokes have loss of brain tissue and are hypoattenuating.Ī noncontrast head CT may identify the early signs of stroke, but most importantly will exclude intracerebral hemorrhage and lesions that might mimic acute ischemic stroke such as tumor or intracerebral hemorrhage. Mass effect and risk of herniation is greatest at this stage. A subacute stroke represents vasogenic edema, with greater mass effect, hypoattenuation and well-defined margins. A thrombus in the proximal middle cerebral artery (MCA) is sometimes seen in the acute phase and appears as hyperattenuation. It is intracellular edema and causes loss of the normal gray matter/white matter interface (differentiation) and effacement of the cortical sulci. They are also termed “early ischemic changes “and were formerly termed “hyper-acute”. 3 Acute stroke represents cytotoxic edema, and the changes can be subtle but are significant. Three main stages are used to describe the CT manifestations of stroke: acute (less than 24 hours), subacute (24 hours to 5 days) and chronic (weeks). Axial nonenhanced computer tomography demonstrates hypoattenuating foci throughout the left sided white matter (arrows) and sulcal effacement in the left MCA territory, consistent with infarction. ![]() Left middle cerebral artery (MCA) infarction. ![]()
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