\"Top of the basilar\" syndrome.
CT shows bilateral cerebellar hemispheric and rostral brain stem infarcts with mass effect on 4th ventricle causing mild hydrocephalus.
Top-of-the-basilar syndrome:
This is the manifestation of upper brainstem and diencephalic ischemia caused by occlusion of the rostral basilar artery, usually by an embolus.
Patients present with changes in the level of consciousness due to involvement of reticular activating system in rostral brainstem infarct. They may experience visual symptoms such as hallucinations and/or blindness. Third nerve palsy and pupillary abnormalities are also frequent. Motor abnormalities include abnormal movements or posturing.