One Size Does Not Fit All: Micro-, Meso-, and Macrobleeds in Cerebral Amyloid Angiopathy.

Introduction: MRI rating criteria for small vessel disease markers include definitions for microbleeds and macrobleeds but do not account for small (<10 mm) hemorrhages with a cystic cavity and/or irregular shape. Such hemorrhages, however, are often present in patients with cerebral amyloid angiopathy (CAA). In this study, we aimed to investigate the frequency, diameter, and volume distribution of these hemorrhages (which we called mesobleeds) in patients with CAA.

Methods: We selected participants with Dutch-type hereditary CAA (D-CAA) and sporadic CAA (sCAA) and scored microbleeds, mesobleeds, and macrobleeds on 3T susceptibility-weighted images MRI. Hemorrhage diameter and volume were calculated in a subset of participants using a semi-automatic tool; their distribution was evaluated on a logarithmic scale.

Results: We included 25 participants with D-CAA (mean age 56 years) and 25 with sCAA (mean age 73 years). In total, 11,007 microbleeds, 602 mesobleeds, and 195 macrobleeds were observed. Eighty-two percent of participants had ≥1 mesobleed. Hemorrhage diameter and volume were calculated in four participants with 272 microbleeds (median diameter 1.52 mm, volume 0.004 mL), 84 mesobleeds (median diameter 5.61 mm, volume 0.06 mL), and 37 macrobleeds (median diameter 19.58 mm, volume 1.33 mL). Mesobleed diameter and volume were larger than microbleeds (optimal cut-off 0.02 mL) but showed overlap with macrobleeds.

Conclusion: Hemorrhages <10 mm with an irregular shape and/or cystic cavity are frequently found in participants with CAA and have a distinct diameter and volume distribution. We propose to name these hemorrhage mesobleeds and to rate them separately from micro- and macrobleeds. Future research is necessary to investigate their pathophysiology and prognostic value.