[Brain microbleeds - definition, pathophysiology and the consequences].

Brain microbleeds are defined as small, circular hypointense changes in T2-sequensec of brain MRI, well demarcated from the surrounding tissue. They represent the phagocytized products of blood distribution extravasated from pathologically altered vessels. The echo-T2-dependent gradient (GRE) and magnetic susceptibility testing (SWI) sequences are usually used to visualize them. The pathogenesis of microbleeds very complex but angiopathy associated with arterial hypertension and cerebral amyloid angiopathy play a special role. Atherosclerotic lesions and inflammatory processes are also important. Microbleeds can be found in healthy people as well as in many disorders such as hypertension, Alzheimer's disease or other types of dementia. Their prevalence increases with age. Microbleeds may have a multidimensional effect on the surrounding brain tissue. It is suggested that they disrupt both the brain structure and the electrical function of neurons. In this review article we present current knowledge on the cerebral microbleeds.