microhemorrhages

Microhemorrhages, commonly referred to as cerebral microbleeds when they occur in the brain, are small foci of prior bleeding from the brain’s microvasculature. Pathologically, they consist of deposits of hemosiderin around sites of tiny blood leakage, reflecting previous hemorrhage. On magnetic resonance imaging, microhemorrhages appear as punctate, hypointense (dark) foci typically less than about 2 millimeters in diameter, most readily detected with susceptibility-weighted imaging (SWI) or T2*-weighted sequences. They are often distributed along vascular territories corresponding to their underlying cause.

Most cerebral microhemorrhages result from small vessel disease. Hypertensive arteriopathy tends to produce deep or infratentorial microbleeds in structures such as the basal ganglia, thalamus, brainstem, and cerebellum. Cerebral amyloid angiopathy commonly causes lobar microbleeds near the cortex and subcortical white matter. Microhemorrhages are also observed with aging and can be associated with other conditions that affect small vessels, including certain inflammatory or degenerative disorders, trauma, and after reperfusion in ischemic syndromes.

Imaging plays a central role in detection. SWI and T2*-weighted MRI sequences are most sensitive for identifying microbleeds; CT is less reliable for small foci. Histologically, microhemorrhages are characterized by hemosiderin-laden macrophages surrounding a small area of prior red blood cell leakage.

Clinical significance rests on their use as markers of cerebral small vessel disease and risk stratification. The presence and pattern of microhemorrhages can influence prognosis and management, particularly in decisions about anticoagulation or thrombolysis, and they correlate with cognitive impairment in various vascular brain syndromes.