Cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is a cerebrovascular disorder that tends to manifest in normotensive elderly patients. It is common and most often presents clinically as an intracerebral haemorrhage ¹. It is usually not associated with systemic amyloidosis.

Epidemiology 

CAA can be found on screening gradient imaging in up to 16% of asymptomatic elderly patients ⁴. Autopsy studies have found a prevalence of approximately 5-9% in patients between 60 and 69 years, and 43-58% in patients over the age of 90 ⁴. 

Clinical presentation

Symptomatic clinical presentation is usually with an intracerebral haemorrhage, found in 40% of autopsy proven cases of CAA ¹. This is often in the form of microhaemorrhages. Of all patients with cerebral haemorrhage, CAA is found in 4-10% of cases ². Vessel damage can also result in ischaemic leukoencephalopathy ¹.

Occasionally mass like lesions have been reported ³ (not to be confused with cerebral amyloidosis seen in patients with systemic amyloidosis). 

The Boston criteria ⁷are a combination of clinical, radiographic and pathological criteria which are used to assess the probability of CAA.

Pathology

CAA is characterised by the deposition of ß-amyloidin the media and adventitia of small and medium sized arteries of the cerebral cortex and leptomeninges ⁴. This is associated with with associated fibrinoid degeneration, and microaneurysm formation ¹. Amyloid is an eosinophylic, insoluble protein, located in the extra-cellular space, and stains with Congo red yielding apple green birefringence when viewed with polarized light ³. It is important to note that amyloid deposition is also encountered in other clinical scenarios including spongiform encephalitis ¹: 

Associations

• Alzheimer's disease 
  • pathological of CAA changes are seen in ~80% of those with Alzheimer's disease ⁵ 
  • ~40% of those with CAA have Alzheimer's dementia type symptoms  

Radiographic features

Findings reflect the various manifestations of the disease.

• microhaemorrhages
  • not seen on CT
  • small focal regions of signal drop out best seen on T2* sequences (gradient echo, echo-planar, SWI) as regions of blooming
  • may be difficult to see on conventional T1 and T2 sequences ⁴
  • tend to be subcortical (grey-white matter junction) rather than basal ganglia (c.f. hypertensive microhaemorrhages) ⁴
• cerebral haemorrhage
  • usually superficial (lobar) 
  • appearance will vary according to age of bleed (see blood on MRI)
• leukoencephalopathy
  • diffuse low density of the white matter 
  • diffuse white matter hyperintensity on T2 weighted scans ^1,6
• focal mass ³
  • low density on CT with mass effect (differential diagnosis : glioma)
  • T1
    • low signal
    • non-enhancing
  • T2
    • high signal
    • evidence of haemorrhage not necessary

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