• cerebral microbleeds (CMBs) or cerebral microhemorrhages are characterized by hemosiderin deposits caused by small hemorrhages, and may serve as a radiologic biomarker of small vessel disease (SVD)
    • black lesions on blood-sensitive MRI sequences (GRE T2* or SWI images)
  • often found incidentally; the prevalence increases with age
    • general population ∼ 10-15%   (Sveinbjornsdottir, 2008)
    • 6.5% of the individuals aged 45-50 years
    • up to 40% of the population > 80 years    [Poels, 2009]
    • incidence of CMBs in AD is 20-43%; in vascular dementia, it is up to 85%!   [Seo, 2007]
  • microhemorrhages are associated with:
    • older age (prevalence increasing significantly after the age of 75)
    • hypertension
    • smoking
    • white matter disease and lacunar stroke
    • previous ischemic stroke or intracerebral hemorrhage (ICH)
    • COVID-19 leukoencephalopathy (mostly in critically ill patients) (Agarwal, 2020)
  • a high number of microbleeds is associated with an increased risk of:

  • increased risk of progression is common in:

Cerebral microbleeds and the risk of hemorrhage

  • the risk of ICH increases with the number of CMBs
    • ≥ 5 CMBs – OR for ICH 2.8
    • ≥ 10 CMBs – OR for ICH 5.5!
  • according to the CROMIS-2 trial, the risk of bleeding in patients with CMBs is 9.8/1000 vs. 2.6/1000 patient-years (adjusted hazard ratio 3·67, 95% CI 1·27–10·60) [Wilson, 2018]
  • the incidence of ICH is up to 5%/year in cases with multiple lobar CMBs [Van Etten, 2014]


  • subcortical (mainly caused by arteriolopathy)  → Binswanger’s disease
  • cortical (mostly caused by CAA – with an increased risk of lobar hemorrhage)
  • combined (combination of CAA and arteriolosclerosis or rather arteriolosclerosis alone) [Jung, 2020]

Radiographic features of hypertensive angiopathy

  • cerebral microbleeds (predominantly in the deep grey nuclei and brainstem)
  • subcortical infarcts (lacunar) in the deep grey nuclei, white matter, and brainstem
  • dilated perivascular spaces in the basal ganglia
  • white matter hyperintensities and hyperintensities in the deep grey nuclei and brainstem on T2

Diagnostic evaluation

  • detectable only on specific sequences, such as gradient-recalled echo (GRE) and susceptibility-weighted imaging (SWI)
    • microbleeds are inapparent on other MRI sequences and CT
  • black, round, or oval lesions that are 2-5 mm in diameter, associated with a blooming artifact, which overestimates the size of the lesions

Greenberg’s criteria (Roob, 1999)

  • black round or ovoid lesion with blooming on GRE/SWI
  • devoid of signal hyperintensity on T1- or T2-weighted sequences
  • at least half surrounded by brain parenchyma
  • distinct from other potential mimics such as iron/calcium deposits, bone, or vessel flow voids
  • clinical history, excluding traumatic diffuse axonal injury

Blooming artifact

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Use GRE or SWI sequence?

  • both techniques are used to detect blood products and calcifications due to their sensitivity to local susceptibility effects
  • T2*-weighted gradient-echo (GRE) sequences operate in 2D multi-slice mode, using relatively long TR’s, low flip angles, and relatively long TE’s
  • modern susceptibility-weighted imaging (SWI) methods are based on GRE sequences but include numerous enhancements for improved differentiation between paramagnetic (hemorrhage) and diamagnetic (calcification) substances
  • SWI is superior to GRE (particularly in the diagnosis of traumatic brain injury and microvascular angiopathy)
  • however, SWI sequences take longer than standard GRE and are more susceptible to motion artifacts

Cerebral amyloid angiopathy (CAA) on GRE

Cortical cerebral microbleeds and lobar hematomas in patient with cerebral amyloid angiopathy
Cortical cerebral microbleeds (CMBs)
Cortical cerebral microbleeds (CMBs) on SWI sequence

Differential diagnosis

  • calcium and iron deposits (calcium is hyperdense on the CT scan)   PKAN “eye-of-the-tiger” - bilateral central hyperintense areas within a hypointense region in the medial globus pallidus (T2 a GRE)  PKAN “eye-of-the-tiger” - bilateral central hyperintense areas within a hypointense region in the medial globus pallidus (T2)
    • diseases with an accumulation of iron  see here
  • flow void from veins or small arteries on the cross-section  Subcortical CMB and artery cross section (green arrow)
    • follow the continuum of the vessel on adjacent slices
  • cavernous malformation (cavernoma)  Cerebral cavernous malformation with a typical popcorn appearance
  • malignant melanoma metastases   The malignant melanoma
    • T1 – hyperintense (due to bleeding and/or the presence of melanin)
    • T2 – hypointense
    • T1 C+ – diffuse or ring-like saturation
    • T2*- hypointense
  • pneumocephalus and gas embolism
  • metallic emboli from mechanical heart valve (very rare)


  • no specific therapy
  • strict treatment of hypertension
  • careful indication and monitoring of anticoagulant (preferably use DOACs) and antiplatelet therapy (avoid DAPT if possible)
  • the risk of symptomatic intracranial hemorrhage (sICH) may increase after thrombolytic therapy in patients with cerebral microbleeds (CMBs)
  • CMBs < 10  ⇒  IVT seems safe (ESO guidelines 2021) (AHA/ASA 2019 IIa/B-NR)
  • CMBs > 10 ⇒ IVT carries a higher risk of ICH; the expected benefit of treatment must outweigh the risk ⇒ consider IVT in patients with a severe stroke (ESO guidelines 2021)
    • a small study retrospectively found a slightly increased risk (3%) of bleeding in patients with microbleeds on GRE [Fiehler, 2007]
    • an increased risk of bleeding is associated with CAA as a cause of microbleeds
  • no MRI screening is recommended to assess CMB burden before making a treatment decision regarding IVT (ESO guidelines 2021)
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  • no definitive guidelines exist for antiplatelet use in patients with CMBs
  • single antiplatelet therapy – seems a safe and beneficial approach (RESTART trial subanalysis) [Salman, 2019]
  • dual antiplatelet therapy (DAPT) – individual risk-benefit analysis is crucial (DAPT is acceptable after recent stenting, etc.)

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Cerebral Microbleeds (CMB)