Cerebral blood flow and metabolism associated with cerebral microbleeds in small vessel disease

Objective: Cerebral microbleeds (CMBs), probably reflecting microangiopathy, have not yet sufficiently been examined in association with cerebral blood flow (CBF) and metabolism. We investigated the relationships between CMBs, and CBF and metabolism in symptomatic small vessel disease. Methods: We enrolled 22 patients with symptomatic small vessel disease without severe stenosis (>50 %) in major cerebral arteries. Volumes of white matter lesions (WMLs) and number of CMBs were assessed on images of fluid-attenuated inversion recovery and gradient-echo T2*-weighted magnetic resonance imaging, respectively. Patients were divided into two groups according to the median number of CMBs (group I <5, n = 10; group II ≥5, n = 12). Parametric images of CBF, cerebral metabolic rate of oxygen (CMRO₂), oxygen extraction fraction and cerebral blood volume were estimated using positron emission tomography and ¹⁵O-labeled gases. The functional values in the cortex–subcortex, basal ganglia, and centrum semiovale were compared between the two groups. Results: Volumes of WMLs of group II were larger than those of group I (median: 38.4; range: 25.1–91.5 mL vs. median: 11.3; range: 4.2–73.4 mL, p = 0.01). In the centrum semiovale, the mean CBF of group II was significantly lower than that of group I (12.6 ± 2.6 vs. 15.6 ± 3.3 mL/100 g/min, p = 0.04). In the other regions, there were no significant differences in either CBF or CMRO₂ between the two groups. Conclusions: Our study indicated that increases in the number of CMBs with larger volumes of WMLs were associated with cerebral ischemia in the deep white matter in patients with symptomatic small vessel disease.