Intracranial MR Dynamics in Clinically Diagnosed Alzheimer's Disease: The Emerging Concept of Pulse Wave Encephalopathy

As increasingly shown in neuropathological and predementia clinical studies, cognitive decline with altered intracranial dynamics can fulfill current clinical criteria of dementia of the Alzheimer's type (DAT) and there is a marked pathogenic complexity of this epidemic syndrome. Whereas structural studies only suggest the unexpected frequency of cerebrovascular changes in late life DAT, flow quantification MR sequences now offer a great opportunity of in vivo accurate analysis of cerebrovascular function. Their first applications have allowed development of a modern concept of the intracranial dynamics; a complex windkessel system allows two processes that are crucial to insure brain oxygenation and nutrition, a periodic systolic marked expansion of the intracranial blood compartment within the rigid cranial cavity on the one hand, a marked dampening of the arterial pulse wave before it reaches capillary level on the other hand. This modern concept has allowed better understanding of two archetypes of windkessel failure or so-called pulse wave encephalopathy, normal pressure hydrocephalus and subcortical arteriosclerotic encephalopathy. Dynamic MRI may now help to detect and classify distinct patterns of cerebrovascular dysfunction in DAT. This dynamic approach helps to understand the major association between aging and DAT as well as the increasingly recognized overlap between Alzheimer's pathology, normal pressure hydrocephalus and arteriosclerotic neurodegeneration. Evidence of such a great variety of disturbances in intracranial dynamics behind a single clinical syndrome of DAT can greatly impact therapeutic research on this devastating disorder.