Amyloid related imaging abnormalities (ARIA)

Last revised by Assoc Prof Frank Gaillard on 19 Aug 2021

Amyloid related imaging abnormalities (ARIA) represents a variety of imaging features identified in patients with Alzheimer disease being treated with novel amyloid lowering therapies such as the monoclonal antibodies bapineuzumab, solanezumab and aducanumab 1-4

In most instances, ARIA is detected incidentally on imaging. Some patients describe various symptoms related, presumably, to cerebral edema and irritation including headaches, vomiting, confusion, and gait disturbance 4

Although the mechanism underlying these phenomena remain to be fully understood they are believed to be related to the breakdown of the blood-brain barrier as a result of the mobilization of the amyloid previously deposited in blood vessels 1,2

The likelihood of developing hemorrhagic lesions correlates with the number of APOE ε4 alleles, also known to correlate with increased risk of cerebral amyloid angiopathy, as well as concurrent use of antithrombic ages 3

Amyloid related imaging abnormalities (ARIA) are primarily identified on MRI, although more pronounced changes would be expected to be visible also on CT. 

ARIA is divided into two subtypes, based on the presence of edema and hemorrhages although they frequently co-exist 1

ARIA-E (e for edema) is characterized by the presence of 1:

  • parenchymal edema (ARIA-E edema)
    • high T2/FLAIR signal involving subcortical white matter and/or cortex
    • no abnormal diffusion restriction
    • no parenchymal enhancement, but subtle overlying leptomeningeal/cortical enhancement may be seen
  • sulcal effusions (ARIA-E effusions)
    • high FLAIR signal (non-attenuating) in sulci often overlying an area of parenchymal edema

Although ARIA-E can occur bilaterally, it is most frequently (~2/3) unilateral 1

ARIA-H (h for hemorrhage) is usually seen in combination with ARIA-E and is characterized by the presence of 1,4:

  • parenchymal microhemorrhages (most common)
  • sulcal/leptomeningeal hemosiderin deposits

No treatment is usually required, other than withholding further treatment with the amyloid-lowering agent 4. In occasional cases, steroids have been given to reduce cerebral edema 4.

Both parenchymal edema and sulcal effusions forms of ARIA-E are usually transient resolving over a number of months 1. Blood products, in contrast, 

  • cerebral amyloid angiopathy related inflammation (CAA-ri)
    • the imaging features of ARIA are essentially identical, with the only real distinguishing feature being clinical context; namely, ARIA occurs in individuals being treated with amyloid lowering agents
  • posterior reversible encephalopathy (PRES)
    • similar, usually posterior, can involve deep grey matter
    • usually in the setting of severe hypertension or other risk factors
    • usually no microhemorrhages
  • cerebral infarction
    • diffusion restriction during the acute phase
    • prominent enhancement during the sub-acute phase
  • peri-lesional edema (e.g. around metastasis, primary tumor, abscess)
    • underlying lesion usually visible 

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