1) large-vessel atherosclerosis

2) small-vessel disease

3) cardioembolism (due to medium or high risk cardiac embolic source)

4) other specific etiology, including non-atherosclerotic vasculopathies (dissection of extracranial arteries, migraine, inflammatory vasculopathy associated with illicit drugs, infections, connective tissue disease...) and hypercoagulable states

5) undetermined etiology, which was further classified into 3 subtypes
5.a) two or more possible causes identified (undetermined, multiple possible etiologies);
5.b) negative evaluation after exhaustive etiological diagnostic workup which excluded atherothrombotic, lacunar, cardioembolic or specific etiologies; the complete workup includes: cerebral imaging studies as computed tomography (CT) scanning or magnetic resonance imaging, echocardiography, extracranial cerebrovascular Doppler studies, a hemostatic test and arteriography, if needed (undetermined, complete evaluation or unknown etiology)
5.c) incomplete evaluation.