Lacunar infarcts are small infarcts in the deeper parts of the brain (basal ganglia, thalamus, white matter) and in the brain stem. They are responsible for about 20 percent of all strokes. They are caused by occlusion of deep penetrating branches of major cerebral arteries and are particularly common in hypertension and diabetes, which are associated with severe atherosclerosis of small vessels and small vessel disease (see below). A small lacunar infarct (e.g., one involving the internal capsule) can cause as severe a neurological deficit as can a much larger hemispheric infarct but without the life-threatening cerebral edema that is seen in the latter.