**2. Pathophysiology**

CAA is characterized by deposition of β-amyloid protein in media and adventitia of small and medium-sized cortical, subcortical, and leptomeningeal vessels, with sparing of similar-sized vessels in the deep white matter. [2] The complex structural changes in the vessel wall related to β-amyloid deposition include endothelial dysfunction, loss of smooth muscle cells, fibrinoid necrosis, vessel wall fragmentation (fragile vessel) and microaneurysm formation. All these factors predispose the patient to repeated episodes of blood vessel leakage and frank hemor‐ rhages in response to sudden increase in blood pressure or minor trauma. [3,4] CAA related inflammation (termed as cerebral amyloid angitis or cerebral amyloid inflammatory vascul‐ opathy) is typically perivascular and may be associated with frank vasculitis. β-amyloid deposition causes vessel wall thickening and subsequent luminal narrowing leading to ischemic changes. [2] The deposition may also impair the perivascular drainage, leading to dilatation of perivascular spaces (also known as Virchow Robin spaces) within the lobar region and in deep cerebral white matter. The enlarged perivascular spaces, a potential useful neuroimaging marker of CAA, can reach several millimeters in diameter and may be visible on brain imaging. [5,6] Histologically, β-amyloid deposits stained with Congo red show classic yellow-green birefringence under polarized light. [3]

**4. Neuroimaging correlates of CAA**

**Full postmortem examination demonstrating:** -Lobar, cortical, or corticosubcortical hemorrhage

parameters. [11]



**Clinical data and MRI or CT demonstrating:**

**Clinical data and MRI or CT demonstrating:** -Single lobar, cortical, or corticosubcortical hemorrhage




**Table 1.** Boston criteria for diagnosis of CAA-related hemorrhage

**Definite CAA**

**Probable CAA**

**Possible CAA**



**The Boston criteria** (table 1) was first proposed in 1990 in order to standardize the diagnosis of cerebral amyloid angiopathy. They comprise of combined clinical, imaging and pathological

Cerebral Amyloid Angiopathy http://dx.doi.org/10.5772/58461 43

Recognition of the imaging findings of CAA is important for correct diagnosis. The important imaging correlates of CAA include: (i) large intracranial hemorrhages (ICHs), (ii) cerebral microbleeds (CMBs), (iii) convexity subarachnoid hemorrhages (cSAH), (iv) cortical superfi‐

The majority of ICHs (>75%) in elderly are spontaneous due to rupture of small arteries affected by either of the two processes; the hypertensive arteriopathy or CAA. Distribution of ICH reflects the underlying microangiopathy. Hypertensive arteriopathy is characterized by lipohyalinosis and fibrinoid necrosis of lenticulostriate perforators located in deep gray nuclei (i. e. basal ganglia, thalami) and infratentorial location (i. e. pons). In contrast, CAA related ICH is preferentially lobar (any lobe may be involved); less commonly involves the cerebellum and rarely the deep nuclei or the brainstem. [12] CAA-related ICH represents 2% of all ICH and is an important cause of hemorrhage in normotensive elderly patients without trauma.

cial siderosis, (v) white matter changes (leukoaraiosis), and (vi) prominent VRSs.
