Neurovascular Emergencies: Imaging Diagnosis and Neurointerventional Therapy

Acute Ischemic Stroke Acute ischemic stroke accounts for the majority of acute neurovascular emergencies, with approximately 795,000 cases of new or recurrent stroke occurring annually. An estimated 6.6 million Americans over the age of 20 have had a stroke. In the United States, a stroke occurs every 40 seconds while a stroke-related death occurs every 4 minutes. The first-line imaging examination for stroke is unenhanced head CT to exclude a brain mass or intracranial hemorrhage and to identify early signs of ischemia. These early signs of ischemic stroke on CT include hypoattenuation of the lentiform nuclei and insular cortex, loss of graywhite differentiation, sulcal effacement, and dense vessels representing intra-arterial thrombus (Figure 1). CT or MR angiography can identify arterial occlusion. CT perfusion may be performed to differentiate infarcted from viable brain tissue at risk of ischemia that may benefit from early intervention. On MRI, early hyperacute ischemia, defined as occurring within 0 to 6 hours of arterial occlusion, demonstrates restricted diffusion. Fluid-attenuated inversion recovery (FLAIR) signal can be variable in this period. Late hyperacute stroke, occurring within 6 to 24 hours of arterial occlusion, also will restrict diffusion; however, there is usually high FLAIR signal and T1 hypointensity after 16 hours. Acute stroke presenting from 24 hours to 1 week after symptom onset will demonstrate restricted diffusion, FLAIR hyperintensity, low T1 signal, and high T2 signal. The intensity of restricted diffusion diminishes as the stroke evolves from acute to chronic, and arterial enhancement can occur at any time point. The mainstay of stroke therapy is IV recombinant tissuetype plasminogen activator (tPA), which should be administered before endovascular treatment and within 4.5 hours of symptom onset to improve outcome. Unenhanced CT should be performed before any stroke treatment to exclude the contraindications of acute intracranial hemorrhage or brain tumor. Patients are eligible to receive endovascular therapy with a stent retriever device if they meet specific criteria (Table 1). The Alberta Stroke Program Early CT Score (ASPECTS) may affect eligibility for tPA therapy, which quantifies ischemic changes in the middle cerebral artery (MCA)