Imaging description

CT has an unparalleled track record in the detection of intracranial hemorrhage and therefore is the first imaging study obtained in this setting. In addition to excluding intracranial hemorrhage, CT may help demonstrate early signs of acute ischemic stroke (AIS), such as insular ribbon sign, hyperdense cerebral artery sign, sulcal effacement, and development of acute parenchymal low attenuation (Fig. 3.1). Patients who have advanced signs of infarction involving more than one-third of the middle cerebral artery (MCA) territory are generally excluded from intravenous tissue plasminogen activator (tPA) therapy because of a higher risk for hemorrhagic conversion.

Advanced imaging as a triage tool for selecting patients for intravenous (IV) or intra-arterial (IA) stroke therapies beyond 3 hours is a focus of evaluation of many ongoing clinical trials [1]. Central to the idea of advanced imaging is to obtain a precise measure of the area of ischemic core versus ischemic but still viable tissue that is at risk for infarction in the absence of early recanalization (penumbra). It can be argued that patients can only benefit from recanalization if there is a relatively modest area of already infarcted tissue and significant (ideally >20% of area of core infarction) ischemic tissue that can be potentially salvaged.