Sequelae of Remote Microhemorrhage (Cerebral Microbleeds)
Remote cerebral microhemorrhages are associated with increased risk of recurrent intracerebral hemorrhage, cognitive decline, dementia, and all-cause mortality, with the clinical significance determined primarily by their number and location (lobar versus deep/infratentorial). 1
Recurrent Hemorrhagic Stroke Risk
Microbleeds substantially increase the risk of future intracerebral hemorrhage (ICH), particularly when multiple microbleeds are present or when they occur in lobar locations suggesting cerebral amyloid angiopathy (CAA). 1
The 2022 AHA/ASA guidelines identify the presence, number, and lobar location of microbleeds as reasonable risk factors to incorporate into decision-making for ICH recurrence. 1
Four or more microbleeds (<10 mm diameter) are exclusionary criteria for antiamyloid monoclonal antibody therapy due to increased risk of amyloid-related imaging abnormalities (ARIA). 1
In CAA-related ICH, microbleeds predict a recurrence risk of 7.4% per year, substantially higher than the 1.1% per year in non-CAA ICH. 1
Cognitive Impairment and Dementia
Microbleeds are associated with approximately 2-fold increased risk of incident dementia in population-based studies with long-term follow-up. 1
The presence of microbleeds correlates with executive dysfunction in patients with ischemic cerebrovascular disease. 2
Vascular cognitive impairment occurs in 38% of stroke survivors within the first year, and microbleeds contribute to this burden as markers of underlying small vessel disease. 1
Microbleeds are more prevalent in individuals with Alzheimer's disease dementia and are now recognized by the NIH as a major factor in Alzheimer's disease pathology. 3
Mortality Risk
The presence of microbleeds, particularly deep or infratentorial microbleeds, is associated with increased all-cause mortality (hazard ratio 1.87) independent of vascular risk factors. 4
Deep or infratentorial microbleeds strongly associate with cardiovascular mortality (hazard ratio 4.08), suggesting they mark severe underlying vascular pathology. 4
Mortality risk increases with increasing number of microbleeds, indicating a dose-response relationship. 4
Ischemic Stroke Risk
Microbleeds are associated with approximately 4-fold increased risk of incident symptomatic stroke in population-based studies. 1
In patients with ischemic cerebrovascular disease, microbleed number and location may predict the occurrence of lacunar infarction. 2
Location-Specific Implications
Lobar Microbleeds
Lobar microbleeds suggest cerebral amyloid angiopathy and confer the highest risk of recurrent lobar ICH. 1, 2
Decision analysis studies recommend against anticoagulation even in the presence of atrial fibrillation when lobar microbleeds indicate CAA pattern. 5
Deep or Infratentorial Microbleeds
Deep or infratentorial microbleeds typically indicate hypertensive vasculopathy and are associated with worse mortality outcomes. 2, 4
These locations are particularly associated with increased cardiovascular mortality risk. 4
Antithrombotic Therapy Considerations
Small numbers of microbleeds (<5) show no statistically significant increase in symptomatic intracranial hemorrhage risk with intravenous thrombolysis, and antithrombotic therapy can generally proceed. 5
Multiple microbleeds (>5) represent underdetermined risk, requiring extreme caution with antithrombotic therapy. 5
The 2022 AHA/ASA guidelines note that some data suggest microbleeds represent markers of bleeding-prone angiopathy and increased risk of hemorrhagic transformation after antithrombotic and fibrinolytic therapy, though other studies have not found increased risk with small numbers. 1
Neuropsychiatric Sequelae
Microbleeds are thought to progressively impair neuronal function, potentially contributing to geriatric psychiatric syndromes and gait disorders. 3
The presence of microbleeds may contribute to post-stroke depression and anxiety, though specific data on this relationship remain limited. 1
Common Pitfalls
The number of microhemorrhages, while helpful for diagnosis, is not currently thought to be associated with injury severity or outcomes in traumatic brain injury, distinguishing traumatic from spontaneous microbleeds. 6
Microbleeds cannot be reliably detected on CT; gradient-echo or susceptibility-weighted MRI sequences are required for detection. 1
Conclusions regarding significance and associated risks must be made based on the population examined (e.g., CAA versus hypertensive vasculopathy, stroke versus asymptomatic elderly). 2