Microbleeds Versus Macrobleeds

Abstract

Background and Purpose-Small, asymptomatic microbleeds commonly accompany larger symptomatic macrobleeds. It is unclear whether microbleeds and macrobleeds represent arbitrary categories within a single continuum versus truly distinct events with separate pathophysiologies. Methods-We performed 2 complementary retrospective analyses. In a radiographic analysis, we measured and plotted the volumes of all hemorrhagic lesions detected by gradient-echo MRI among 46 consecutive patients with symptomatic primary lobar intracerebral hemorrhage diagnosed as probable or possible cerebral amyloid angiopathy. In a second neuropathologic analysis, we performed blinded qualitative and quantitative examinations of amyloid-positive vessel segments in 6 autopsied subjects whose MRI scans demonstrated particularly high microbleed counts (Ͼ50 microbleeds on MRI, nϭ3) or low microbleed counts (Ͻ3 microbleeds, nϭ3). Results-Plotted on a logarithmic scale, the volumes of 163 hemorrhagic lesions identified on scans from the 46 subjects fell in a distinctly bimodal distribution with mean volumes for the 2 modes of 0.009 cm 3 and 27.5 cm 3 . The optimal cut point for separating the 2 peaks (determined by receiver operating characteristics) corresponded to a lesion diameter of 0.57 cm. On neuropathologic analysis, the high microbleed-count autopsied subjects showed significantly thicker amyloid-positive vessel walls than the low microbleed-count subjects (proportional wall thickness 0.53Ϯ0.01 versus 0.37Ϯ0.01; PϽ0.0001; nϭ333 vessel segments analyzed). Conclusions-These

Ischemic brain injury in cerebral amyloid angiopathy

“…32,33 According to these criteria probable CAA is defined by the presence of multiple strictly lobar hemorrhages on T2* gradient-recalled echo or susceptibility weighted MRI. These may involve both macrohemorrhages and micro-hemorrhages, 34 herein referred to as 'ICH' and 'microbleeds', respectively. Radiologichistopathologic studies have confirmed that microbleeds often reflect hemosiderin deposits from old microhemorrhages, and sometimes acute extravasations of red blood cells, although not invariably.…”

Prevalence and mechanisms of cortical superficial siderosis in cerebral amyloid angiopathy

“…4,16 Prior symptomatic ICH was defined as a symptomatic stroke syndrome associated with imaging evidence of a corresponding "macro" ICH (.5 mm in diameter on T2*-GRE). 15 Asymptomatic prior ICH (.5 mm in diameter on T2*-GRE MRI) was also noted: chronic ICH was defined on neuroimaging as ICH with no acute bleeding identified on either CT or MRI scans. Acute convexity subarachnoid hemorrhage (cSAH) was defined as linear hypointensity in the subarachnoid space affecting one or more cortical sulci of the cerebral convexities on T2*-GRE sequences with corresponding hyperintensity in the subarachnoid space on T1-weighted or FLAIR images.…”

Cortical superficial siderosis and intracerebral hemorrhage risk in cerebral amyloid angiopathy

“…17 Asymptomatic or symptomatic prior ICH (.5 mm in diameter on T2*-GRE MRI) was also noted. 18 cSS was defined as linear residues of chronic blood products in the superficial layers of the cerebral cortex showing a characteristic "gyriform" pattern of low signal on T2*-GRE images, without corresponding hyperintense signal on T1-weighted or FLAIR images (i.e., without acute subarachnoid hemorrhage). We did not include cSS contiguous with any ICH.…”