Which histologic findings are characteristic of cerebral amyloid angiopathy (CAA)?

Updated: Dec 19, 2018
  • Author: Ravi S Menon, MD; Chief Editor: Helmi L Lutsep, MD  more...
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Histologic examination is required for the definitive diagnosis of cerebral amyloid angiopathy (CAA). Pathologic samples are obtained from hematoma evacuation, cortical biopsy, or postmortem specimens. The disease process may be diffuse, however, so pathologic data may be lacking even in biopsy cases. (Brain biopsy has a sensitivity of 53% and a negative predictive value of 70%.)

The presence of vascular amyloid is a sensitive marker for CAA-related hemorrhage. β-amyloid consists of twisted β-sheet fibrils in a vessel wall. It is a homogenous, intensely eosinophilic material that gives a smudged appearance by light microscopy. When stained with Congo red and visualized under polarized light, it gives a characteristic yellow-green (ie, apple green) birefringence. When thioflavin T and S are used and visualized with ultraviolet light, amyloid appears fluorescent.

The presence of fibrinoid necrosis in amyloid-laden vessels is relatively specific for CAA-related intracranial hemorrhage (ICH). CAA, which involves cortical and leptomeningeal vessels, is most common in the parietal and occipital lobes.

Parenchymal features found in the brains of patients with CAA include patchy demyelination and loss of white matter, cortical hemorrhages and infarcts, and neuritic plaques with or without neurofibrillary tangles. Patients with CAA have been found with a progressive increase in white matter lesions; this may suggest a progressive microangiopathy leading to incident lobar hemorrhage. [15] Most patients with CAA-related ICH do not have Alzheimer disease (AD).

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