# Positron Emission Tomography in Cerebral Amyloid Angiopathy: A Scoping Review
## 4 Discussion  
CAA is a cerebrovascular condition characterized by amyloid-\(\beta\) deposition in the walls of cerebral small vessels, leading to an increased risk of ICH. The Boston criteria are commonly used to diagnose CAA, categorizing cases into \"probable\" or \"possible\" based on clinical and imaging findings [5,15]. Probable CAA is often associated with lobar ICH, a hallmark of the disease [5,15]. Amyloid PET imaging has emerged as a valuable tool for detecting amyloid deposition in vivo, aiding in the diagnosis and understanding of CAA. It is a technique that provides a more direct molecular imaging biomarker to identify cerebrovascular amyloid in vivo, which would have clinical implications for accurate early diagnosis, dementia and stroke risk stratification (in ICH and anticoagulation-related ICH), and future disease-modifying strategies [52]. A comprehensive understanding of findings from systematic reviews and meta-analyses highlights the diagnostic and clinical implications of amyloid PET in patients with CAA. Amyloid PET imaging can detect amyloid-\(\beta\) deposition in the cerebral vasculature, providing supportive evidence for CAA diagnosis. Studies have shown that patients with probable CAA and ICH exhibit increased amyloid uptake on PET imaging, particularly in the occipital lobes. This regional distribution differs from that observed in AD, where amyloid deposition is more diffuse. The correlation between amyloid PET findings and CAA-related ICH suggests that amyloid imaging can enhance diagnostic accuracy and potentially guide therapeutic decisions. Systematic reviews have consistently reported that global amyloid-beta deposition is significantly elevated in patients with symptomatic CAA compared to healthy controls and patients with deep intracerebral hemorrhage [24; 25; 26]. For instance, [PERSON] et al. [26] conducted a meta-analysis examining global amyloid PET uptake in CAA patients. The study found a significant increase in the global amyloid burden, with an effect size of 1.18 (95% CI: 1.08-1.28, \(p\) < 0.0001). This finding underscores the extensive amyloid deposition present in the vasculature of CAA patients, a feature that distinguishes the disease from other non-amyloid vascular conditions. Furthermore, amyloid PET imaging has been used to compare amyloid deposition between CAA and AD. Although the global amyloid burden is generally lower in CAA than in AD, the distinct regional distribution patterns in CAA provide essential diagnostic insights. Unfortunately, pathological studies have not found evidence that a pathologically confirmed regional CAA burden contributes significantly to proximal anemtorem regional PiB-PET signal in patients with cognitive decline and without previous ICH, suggesting that amyloid PET imaging for the measurement of cortical amyloid burden is unconfounded by CAA on a lobar level [42]. Similar information is not available for patients with severe CAA phenotypes. A hallmark of CAA is preferential amyloid deposition in the occipital lobes. The meta-analysis by [PERSON] et al. [26] also examined the occipital-to-global uptake ratio, a key metric for assessing the regional distribution of amyloids. When comparing CAA to AD patients, CAA patients exhibited a significantly higher occipital-to-global uptake ratio (mean ratio of 1.10, 95% CI: 1.03-1.19, \(p\) = 0.009). This finding aligns with the clinical presentation of CAA, where occipital lobe-related symptoms, such as visual disturbances and lobar hemorrhages, are more common. These regional differences in amyloid distribution are diagnostically valuable. For example, amyloid PET findings combined with MRI markers, such as cSS or CMBs, enhance the specificity of CAA diagnosis. Several systematic reviews have explored the prevalence of CAA in different populations using both imaging and pathological studies. Findings suggest that imaging-based methods, including amyloid PET, may underestimate the prevalence of CAA compared to pathological methods.