Supplementary Material for: Cerebellar Superficial Siderosis in Cerebral Amyloid Angiopathy on 1.5T T2*-Weighted Imaging

Background: Cerebellar superficial siderosis (SS) has been recently reported to be present in about 10% of both hereditary and sporadic cerebral amyloid angiopathy (CAA) on 3T MRI using primarily susceptibility-weighted imaging. Objectives: Our aim was to assess cerebellar SS in sporadic CAA patients using 1.5T T2*-weighted MRI and to evaluate possible underlying mechanisms. Method: We retrospectively screened MRI scans of sporadic probable CAA patients initially presenting with intracerebral hemorrhage-, acute subarachnoid hemorrhage- or cortical SS-related symptoms between September 2009 and January 2022 registered in our stroke database. Patients with familial CAA were excluded. On 1.5T T2*-weighted MRI, cerebellar SS (including kappa statistics for interobserver agreement) was assessed together with typical CAA hemorrhagic features and with the presence of supratentorial macrobleed and cortical SS adjacent to the tentorium cerebelli (TC) and TC hemosiderosis. Results: We screened 151 patients and finally included 111 CAA patients (median age 77) with cerebellar SS observed in 6 (5%) patients. Cerebellar SS presence was associated with a higher number of supratentorial macrobleeds (median n = 3 vs. n = 1, p = 0.0012), presence of supratentorial macrobleed adjacent to the TC (p = 0.002), and TC hemosiderosis (p = 0.005). Conclusions: Cerebellar SS in CAA patients can be identified on 1.5T T2*-weighted imaging. Associated MRI characteristics suggest contamination from supratentorial macrobleeds.