CAA-related hemorrhage in APP23 mice.a, Hemosiderin staining (blue) in the frontal cortex of a 27-month-old mouse indicative of an old hemorrhage. The section is counterstained with nuclear fast red. B, Perivascular hemosiderin-positive microglia (arrowhead) in close vicinity of a small vessel in a 27-month-old mouse.C, Hemosiderin-positive microglia surrounding an enlarged neocortical vessel of aneurysm-like appearance.d, e, Double-labeling for amyloid (brown) and hemosiderin (blue) localized bleedings to amyloid-laden vessels. f, Evidence for acute hematoma was assessed in H&E-stained sections. A significant hemorrhage (asterisk) in the frontal cortex of a 27-month-old APP23 mouse is shown. g, An adjacent section to f was stained with Berlin blue and revealed an old hemorrhage in the same region. Scale bars: a, 100 μm; b, c, f,g, 50 μm; d, e, 5 μm.