Inclusion Criteria:  ≥55 years of age, acute symptomatic cSAH based on FLAIR and T2*-weighted imaging performed within one month of symptom onset, recent trauma, anticoagulation treatment, pathological blood coagulation tests (activated partial thromboplastin time [aPTT] ratio=patient's aPTT/normal control aPTT] >1.2; or partial thromboplastin time [PTT] <75%) or platelet count (<100 x 109/L),  Exclusion Criteria:  exclusion of underlying non-CAA cSAH causes (e.g. reversible cerebral vasoconstriction syndrome, trauma, cerebral venous sinus thrombosus, aneurysm, primary angiitis of the central nervous system, anticoagulation treatment, pathological blood coagulation tests)