Amyloid-β (Aβ) is produced in the brain throughout life and it accumulates in the cerebral cortex in the elderly and to an excessive degree in Alzheimer's disease. One of the routes for elimination of Aβ is by the interstitial fluid drainage pathway along basement membranes of capillary and artery walls—effectively the perivascular lymphatic drainage pathway for the brain. As arteries in the brain age they become stiffer and perivascular elimination of Aβ fails with consequent accumulation of Aβ in brain parenchyma and in blood vessel walls as cerebral amyloid angiopathy.