This angiopathy consists of the deposition of amyloid in the media and adventitia of small vessels, predominantly in the meninges, cortex, and cortical penetrating vessels. The incidence at autopsy of vascular amyloid deposition in the brain is related to the age of the population studied; rates of 12 percent are cited in patients older than 85 years of age (the same changes are present in more than 25 percent of individuals with Alzheimer disease, but the nature of the amyloid [Aβ40 in the pure cerebrovascular form] is different in the two conditions). The result of this deposition is several large or numerous small cerebral hemorrhages of various ages. There is a propensity for hemorrhages in the posterior parts of the brain. An association has been found with the homozygous APOE ε4/ε4 genotype by Greenberg and colleagues (1995) but others have found an association with the E2 allele. As alluded to in earlier sections on cerebral hemorrhage, cerebral amyloid angiopathy is a cause of otherwise unexplained single of multiple cerebral hemorrhage in older people.
Hemosiderin deposition resulting from multiple small and larger hemorrhages are best visualized with gradient- echo or susceptibility-weighted MRI sequences; they appear as focal spots of abnormal hypointensity on both sequences (Fig. 33-34). Tiny hemorrhages may only be visualized on these sequences and not seen on T1 or T2 MRI sequences, or on CT. The location of the hemorrhages in cerebral amyloid angiopathy, subcortical, frequently posteriorly in the brain, and sometimes subpial, imparts a distinctive imaging pattern that is characteristic of this disease, and quite unlike the pattern of small hemorrhages in the basal ganglia, thalamus, and pons that accumulate in hypertensive disease. In addition to the focal microhemorrhages seen in cerebral amyloid angiopathy, there is frequently cortical gyriform hemosiderosis, reflecting leakage of blood products associated with pial or subpial hemorrhages.
The biology of cerebrovascular amyloid has been summarized by Viswanathan and Greenberg. In our own material, only severe impregnation of vessels with amyloid and fibrinoid change in the vessel wall were associated with hemorrhage (Vonsattel et al). Contrary to previous pronouncements, there is probably no greater risk in evacuating these clots surgically than in the case of other cerebral hemorrhages, but most of them are of a size that allows conservative management and evidence is lacking that surgery improves outcome as discussed earlier.
Reports have emphasized multiple TIA-like syndromes, some with migrainous features such as spreading sensory symptoms that may be the most identifiable but not uniformly present characteristic of the process. They are not consistently related to visible ischemic lesions and may be associated with microhemorrhages and with diffuse white matter changes. In some cases, there is a fairly rapid progression to dementia but that is more characteristic of the inflammatory type of cerebrovascular amyloid discussed just below.