- Three patients became demented after surgery for cerebellar hemorrhage or infarction with acute hydrocephalus. All were inattentive, perseverative, and disoriented. They had difficulty with memory, and trouble solving arithmetic problems or copying geometric figures. None showed aphasia, apraxia, or agnosia, although one had word-finding difficulty. One improved substantially in 6 months; one improved slightly in 1 year, and one did not change. None had persistent hydrocephalus. Acute hydrocephalus may have damaged the periventricular white matter to cause the dementia.