Cerebral microbleeds as a predictor of macrobleeds: what is the evidence?

Cerebral microbleeds on blood-sensitive magnetic resonance imaging sequences have emerged as a common and important marker of small vessel disease. Cerebral microbleeds differ from other imaging manifestations of small vessel disease (e.g. lacunes and leukoaraiosis), as they seem to provide more direct evidence of microvascular leakiness from bleeding-prone arteriopathies, namely hypertensive arteriopathy and cerebral amyloid angiopathy, the two leading causes of spontaneous intracerebral haemorrhage. Thus, cerebral microbleeds in specific sub-populations might provide evidence of an ongoing active small vessel arteriopathy with increased future risk of symptomatic intracerebral haemorrhage ('macrobleeding'). If this hypothesis is correct, it raises clinical dilemmas especially regarding the safety of antithrombotic drug use. Although data so far are limited, the relationship of microbleeds to future macrobleeding (and cerebral ischemia) seems to critically depend on the specific patient population and cerebral microbleeds location and burden, which may reflect the nature and severity of the underlying arteriopathies.