Vascular cognitive impairment - an ill-defined concept with the need to define its vascular component.

New guidelines for the diagnosis of vascular cognitive impairment (VCI) represent an important step in the definition of this clinical entity. These guidelines still remain vague in the definition of "vascular" brain lesions causing cognitive decline, because longitudinal correlative imaging studies are still scarce. In this review we explore which abnormalities are likely to contribute to VCI based on a proven vascular etiology, fast progression and their incidence or progression being related to cognitive decline. Among focal changes visible on standard MRI these features apply for coalescent white matter changes. The evidence for lacunes and microbleeds is much less convincing. Microstructural alterations in normal appearing brain tissue which can be detected by new MRI techniques such as magnetization transfer imaging (MTI), diffusion tensor imaging (DTI) and high resolution MR appear to better correlate with cognitive decline, but the etiology of these changes and their histopathological correlates is still incompletely understood as is their evolution over time. New multimodal image processing such as voxel-based lesion-symptom mapping (VLSM) or combinations of DTI and voxel-based analysis will allow to allocate the lesion patterns that show the greatest covariance with clinical outcome. Such data and more longitudinal correlative data on lacunes and microbleeds will increase our pathophysiologic understanding of VCI including the interplay with primary degenerative processes and will lead to refinement of current VCI criteria.