1. Diagnosis The Boston Cerebral Amyloid Angiopathy Study Group has elaborated guidelines regarding the diagnosis of CAA with ICH. The diagnosis of CAA is classified into 4 levels: definite CAA, highly probable CAA with pathologic evidence, likely CAA, and probable CAA. the first 3 levels require a definite absence of other hemorrhage-causing etiologies; although its validity needs further validation, this guideline has been used clinically. Definite CAA: Complete autopsy reveals evidence of lobar, cortical, or cortico-subcortical hemorrhage and severe CAA. Highly likely CAA with pathologic evidence: clinical data and pathologic histology (by examination of hematoma or cortical biopsy specimens) confirm the presence of hemorrhage with the above-mentioned idiosyncrasies and varying degrees of vascular amyloid deposition. Likely CAA: Patients >60 years of age with clinical data and MRI findings (in the absence of pathological evidence) confirming the presence of multiple hematomas. Probable CAA: In patients >60 years of age, clinical and MRI data suggesting a single lobar, cortical or cortico-subcortical hemorrhage without other etiology, or when multiple hemorrhages are possible but not definitive, or when hemorrhages are present at certain atypical sites. 2. Differential diagnosis The differential diagnosis should include anterior circulation stroke, cardiogenic embolic stroke, cerebral aneurysm, frontal lobe syndrome, frontal and temporal lobe dementia, head trauma, intracranial hemorrhage, partial seizures, post-traumatic seizures, and complications of thrombolytic therapy. Other conditions that remain to be considered include complications of anticoagulation therapy, hematologic disorders, bronchial carcinoma, choriocarcinoma, primary and metastatic CNS tumors, complications of fibrinolytic therapy, hypertension, malignant melanoma, renal cell carcinoma, drug use, and vascular malformations.