His: beta-amyloid in tunica media, w/ yellow-green birefringence under polarized light microscopy when stained w/ Congo red. Fibrinoid necrosis.
Epi: elderly, most common cause of ICH in normotensive elderly
A/w: Down syndrome, Alzheimer’s, spongiform encephalitis, radiation necrosis, and vasculitis
MRI GRE: hypointense, siderosis
Var: cystatin C in familial form instead of amyloid b peptide
a: thickened leptomeningeal vessels in pool of SAH. b: apple-green birefringence on Congo-red & polarized light. c & d: extensive vascular amyloid deposits, fibrinoid necrosis, luminal narrowing, fragmentation of vessels.