Background and PurposeThe clinical significance of the periventricular hyperintensity incidentally found on magnetic resonance images of the brain is questionable. We evaluated resting cerebral blood flow and cerebrovascular dilatory capacity of subjects with asymptomatic periventricular hyperintensities to study their cerebral hemodynamics.Methods Magnetic resonance imaging of the brain was performed in 28 asymptomatic subjects with cerebrovascular risk factors to determine the severity of periventricular hyperintensity. Mean gray matter flow was computed by a "'Xeclearance technique in subjects at rest and after the administration of 1 g acetazolamide. Flow values were correlated with the scores for periventricular hyperintensity.

The centrum semiovale T2 hyperintensities lateralized to the side of carotid occlusion are specific and sensitive for the presence and severity of hemodynamic compromise from carotid occlusive disease.

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At 4 weeks and 8 months following initial symptoms, we performed single-photon emission computed tomography (SPECT) with acetazolamide (ACZ) testing in a patient recovering from acute encephalitis, possibly acute disseminated encephalomyelitis (ADEM). Both regional hypoperfusion at baseline and diminished cerebrovascular reserve were seen after focal hyperintensities had disappeared in magnetic resonance imaging (MRI). The time course of SPECT abnormalities reflected the clinical course more closely than the time course of MRI abnormalities. Thus, persistent cerebral circulatory impairment probably contributed to cognitive and language deficits observed at the subacute stage.

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