Small cystic lesions in the lenticular nucleus, thalamus, and internal capsule are most closely associated with lacunar infarctions, which are most commonly secondary to hypeension. They account for 20% of all strokes. The small aerioles supplying these areas are branches of the middle cerebral aery. They exhibit aeriolar sclerosis, which thrombose and cause microinfarctions (liquefactive necrosis) that leave cystic spaces ranging in size from 1 to 15 mm. Multiple lesions are commonly observed. They account for a number of syndromes including (1) a pure motor hemiparesis if the posterior limb of the internal capsule is infarcted and (2) a pure sensory stroke if the infarct is in the ventrolateral thalamus. In some cases, these infarcts are associated with diabetes mellitus, which also produces small vessel disease.Embolism usually produces hemorrhagic infarctions in the distribution of the middle cerebral aery. They generally occur at the periphery of the cerebral coex.The plaques of a demyelinating disease are softened rather than cystic areas in the brain.Genetic diseases are an uncommon cause of cystic lesions in the brain.Cystic astrocytomas may occur in the cerebellum.