Cerebral microbleeds

Related Subjects: |Neurological History taking | Causes of Stroke

The hemosiderin deposits that comprise microbleeds are superparamagnetic and have considerable internal magnetization when brought into the magnetic field of MRI

About

• Cerebral microbleeds are thought to have potentially important clinical implications in dementia and haemorrhagic stroke and in normal ageing.

Aetiology

• Small foci of chronic blood products in normal (or near-normal) brain tissue, designated here as cerebral microbleeds (CMB)
• Increasing recognitions since the development of MRI techniques tailored to detect magnetic susceptibility.
• Size definitions suggested for discriminating microbleeds from macrobleeds, typically ranging up to a maximum diameter of 5 to 10 mm and in some studies a minimum of 2 mm

Causes

• Normal ageing
• Dementia of Alzheimer's type
• Cerebral amyloid angiopathy: lesions in posterior cortical regions, particularly the occipital lobe
• Hypertensive stroke - lesions in basal ganglia, thalamus, brainstem, and cerebellum
• Calcium and iron deposits
• Flow voids in pial blood vessels seen in sulci
• Cavernous malformations and cavernous malformations
• Metastatic melanoma
• Dffuse axonal injury following head trauma

Investigations

• Both T2*Gradient echo and SWI MR imaging sequences have a high sensitivity for microbleed detection
• It seems that sensitivity in detecting microbleeds was marginally higher on thick-/thin-section SWI compared with T2*.
• SWI is the sequence of choice in microbleed detection.
• Note that areas of low intensity that appear on T2*-weighted MRI are larger than the corresponding hemosiderin deposits, representing the so-called "blooming" effect.

Significance

• Presence of multiple microbleeds seems to suggest an increased risk of a cerebral haemorrhage.
• Their presence may be considered especially in terms of anticoagulation.
• Aetiology may be related to risks. CMB location may be important (deep hemispheric/infratentorial versus lobar only).
• Relationship to CAA and lacunar strokes and small vessels disease is yet to be untangled.

Comparing T2*and SWI

Clearly the right-handed image shows more detail of CAA and microbleeds