The content of this Review is based on the group consensus from a conference entitled “Cerebral Microbleeds: Detection and Definition”. Additional references for this Review were identified through searches of PubMed with the search terms “microbleed(s)”, “microh(a)emorrhage(s)”, or “petechial h(a)emorrhage(s)”; or “gradient-echo”, “T2*”, or “susceptibility” in conjunction with “h(a)emorrhage(s)”, from January, 1966 to October, 2008. References were also identified from the bibliography
ReviewCerebral microbleeds: a guide to detection and interpretation
Introduction
Small foci of chronic blood products in normal (or near normal) brain tissue, known as cerebral microbleeds (CMBs), have become increasingly recognised with the widespread use of MRI techniques that are sensitive to iron deposits.1, 2 Advances in software and hardware have led to substantial increases in the sensitivity of MRI to CMBs and improvements in the criteria for their identification. Another area of recent progress has been the use of sensitive MRI in community-dwelling elderly people, in whom the prevalence of CMBs detected is as high as 11·1–23·5%.3, 4 Data from population-based MRI analyses also suggest connections between normal ageing and asymptomatic stages of age-associated small-vessel diseases, such as hypertensive vasculopathy and cerebral amyloid angiopathy. Despite several comprehensive reviews of CMBs,5, 6, 7, 8, 9 recent advances warrant a new assessment of emerging technical features of image acquisition, specific criteria for lesion identification, and recent data from population-based studies.
Section snippets
Detection of CMBs
CMBs are primarily a radiological construct (ie, small MRI signal voids), but one that is indicative of specific underlying microscopic pathological changes (ie, perivascular collections of haemosiderin deposits that are foci of past haemorrhages). Here, we review advances in MRI for the detection of CMBs, the criteria used to include or exclude MRI lesions as genuine CMBs, and what is known of the correlation between MRI and underlying histopathology. A glossary of commonly used MRI terms is
Vascular pathological changes
One approach to the interpretation of CMBs is to regard them as a marker of accompanying vascular pathological change. Histopathological analyses of the vessels associated with CMBs, done primarily in brains with haemorrhagic stroke, have generally identified two types of vascular pathological changes: hypertensive vasculopathy and cerebral amyloid angiopathy.10, 35, 37 For example, among the 11 brains examined by Fazekas and co-workers,10 advanced hypertensive lipohyalinotic changes were seen
Recommendations and future directions
CMBs are a well defined pathological lesion that can be detected by use of T2*-weighted MRI techniques with high sensitivity (particularly by use of new methods), high reliability (with careful image interpretation and consideration of CMB mimics), and high specificity (proven for conventional T2*-weighted MRI, still to be established for the newer methods). The full brain coverage by MRI probably renders neuroimaging a more sensitive method for CMB detection than are histopathological
Search strategy and selection criteria
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