A 64 year old man with hypertension and atrial fibrillation abruptly developed a right hemiparesis affecting the face, arm and leg, accompanied by a non-fluent aphasia. Within 2 days, his speech was improved, but the hemiparesis remained.

Axial CT scan shows a large hypodensity in left basal ganglia and internal capsule. A large deep infarct such as this can be caused by occlusion of the middle cerebral artery with intact collateral blood supply over the hemisphere. Although watershed infarcts are most often thought of as areas between two major blood vessels, there is a deep watershed area between the superficial cortical arteries and the deep penetrating arteries (see pathologic specimen). A deep infarct of this size is caused by large vessel disease (i.e., thrombosis or embolus) and not by small penetrating artery infarcts (i.e., lacunar strokes) which are much smaller. These lesions are sometimes referred to as giant lacunaes, and other names.