GENERAL CONCEPTS Figure 1 illustrates the writing group s conceptual repre- sentation of ischemic stroke subtypes. Lacunar stroke: Lacunar syndrome, with normal com- puted tomography (CT)/magnetic resonance imaging (MRI) or subcortical stroke measuring <1.5 cm in diam- eter on CT or MRI. Most, although not all, of lacunar strokes are due to small vessel disease. Stroke attributable to small vessel disease: Subcorti- cal stroke measuring <1.5 cm in diameter on CT or MRI without evidence of a concomitant cortical infarct. Cardioembolic stroke: Stroke attributable to arte- rial occlusion from an embolus that presumably arose in the heart. Clinical and brain imaging find- ings are similar to those described in large artery atherosclerosis. Evidence of a previous TIA or stroke in >1 vascular territory supports a clinical diagnosis of cardioembolic stroke. Cryptogenic stroke: An imaging-confirmed stroke with unknown source despite thorough diagnostic assess- ment (including, at a minimum, arterial imaging, echo- cardiography, extended rhythm monitoring, and key laboratory studies such as a lipid profile and hemoglobin A1c [HbA1c]). Stroke caused by large artery atherosclerosis: Ischemic stroke in the vascular distribution of a major intracranial or extracranial artery with >50% stenosis or occlusion on vascular imaging. Clinical findings include those of Table 3. Applying Class of Recommendation and Level of Evidence to Clinical Strategies, Interventions, Treatments, or Diagnostic Testing in Patient Care (Updated May 2019)* CLINICAL STATEMENTS AND GUIDELINES Kleindorfer cerebral cortical involvement or brainstem or cerebellar dysfunction. Cortical and cerebellar lesions and brain- stem or subcortical lesions >1.5 cm are considered potentially caused by large artery atherosclerosis. Diag- nostic studies should exclude potential sources of car- dioembolic embolism. 