ABSTRACT: IMPORTANCE:Cerebral microbleeds (CMBs) are collections of blood breakdown products that are a common incidental finding in magnetic resonance imaging of elderly individuals. Cerebral microbleeds are associated with cognitive deficits, but the mechanism is unclear. Studies show that individuals with CMBs related to symptomatic cerebral amyloid angiopathy have abnormal vascular reactivity and cerebral blood flow (CBF), but, to our knowledge, abnormalities in cerebral blood flow have not been reported for healthy individuals with incidental CMBs. OBJECTIVE:To evaluate the association of incidental CMBs with resting-state CBF, cerebral metabolism, cerebrovascular disease, ?-amyloid (A?), and cognition. DESIGN, SETTING, AND PARTICIPANTS:A cross-sectional study of 55 cognitively normal individuals with a mean (SD) age of 86.8 (2.7) years was conducted from May 1, 2010, to May 1, 2013, in an academic medical center in Pittsburgh; data analysis was performed between June 10, 2013, and April 9, 2015. INTERVENTIONS:3-Tesla magnetic resonance imaging was performed with susceptibility-weighted imaging or gradient-recalled echo to assess CMBs, arterial spin labeling for CBF, and T1- and T2-weighted imaging for atrophy, white matter hyperintensities, and infarcts. Positron emission tomography was conducted with fluorodeoxyglucose to measure cerebral metabolism and Pittsburgh compound B for fibrillar A?. Neuropsychological evaluation, including the Clinical Dementia Rating scale, was performed. MAIN OUTCOMES AND MEASURES:Magnetic resonance images were rated for the presence and location of CMBs. Lobar CMBs were subclassified as cortical or subcortical. Measurements of CBF, metabolism, and A? were compared with the presence and number of CMBs with voxelwise and region-of-interest analyses. RESULTS:The presence of cortical CMBs was associated with significantly reduced CBF in multiple regions on voxelwise and region-of-interest analyses (percentage difference in global CBF, -25.3%; P?=?.0003), with the largest reductions in the parietal cortex (-37.6%; P?
