Amyloid-related imaging abnormalities (ARIAs) are abnormalities observed on neuroimaging in patients with Alzheimer's disease, associated with amyloid-modifying therapies, specifically human monoclonal antibodies such as adecanemab. There are two types of these abnormalities, ARIA-E and ARIA-H. This phenomenon was first observed in clinical trials of bapineuzumab. ARIA-E refers to cerebral edema, which is the breakdown of the tight junctions of endothelial cells of the blood-brain barrier and the resulting accumulation of fluid. In a double-blind trial of the human monoclonal antibody solenizumab, 16 patients, or 0.78%, developed ARIA-E. An additional seven patients developed ARIA-E during an open-label extension of the clinical trial. Side effects of ARIA-E depend on the severity and location of the edema. Symptoms can include headache, mental status changes, confusion, vomiting, nausea, tremor, and gait abnormalities. Aria-H refers to cerebral microbleeds, which accompany small cerebral hemorrhages, usually hemosiderosis. Microbleeds are usually seen as small, round, slightly indented lesions that are small hemosiderin deposits. Some studies define microbleeds as less than or equal to 10 mm, while others define them as less than 5 mm. The prevalence of microbleeds in healthy older adults is about 6%, but this value increases to between 50% and 80% in older adults with cerebrovascular disease.