[en] SPECT and planar images of 35 patients with stroke were compared with images of 26 patients with Alzheimer disease, two with Creutzfeldt-Jakob disease, and one with schizoaffective disorder. Transtentorial diaschisis (TTD) with decreased cerebellar activity was shown in 18 patients with large infarcts of middle cerebral artery (MCA) territory and in four patients with internal capsule and basal ganglia infarcts. No TTD was shown in the 29 patients without stroke and those with small infarcts. Decreased cerebral activity contralateral to cerebral infarct due to interruption of cerebellar flow in TTD was hypothesized. The authors concluded that TTD occurs exclusively in an extensive cerebral infarct of the MCA territory, and an absent cortical perfusion abnormality with presence of TTD may indicate basal ganglia and/or internal capsule infarct