Clinical characterization of symptomatic microangiopathic brain lesions

Microvascular Brain Disease Progression and Risk of Stroke: The ARIC Study

BACKGROUND AND PURPOSE

Data on the significance of combined white matter hyperintensities (WMH)/lacunar brain infarcts, and their progression over time for the prediction of stroke are scarce. We studied associations between the progression in combined measures of microvascular brain disease and risk of stroke in the ARIC study (Atherosclerosis Risk in Communities).

METHODS

Prospective analysis of 907 stroke-free ARIC participants who underwent a brain magnetic resonance imaging (MRI) in 1993 to 1995, a second brain MRI in 2004 to 2006, and were subsequently followed for stroke incidence through December 31, 2017 (median [25%-75%] follow-up 12.6 [8.9-13.4] years). A combined measure of microvascular brain disease was defined at each visit and categorized by progression from first to second brain MRI as no progression; mild progression (increase of ≥1 unit in WMH grade or new lacune), and moderate progression (increase of ≥1 unit in WMH grade and new lacune). All definite/probable ischemic or hemorrhagic incident strokes occurring after this second MRI, and through 2017, were included. Associations between microvascular brain disease, progression in the combined measures, and stroke incidence were studied with Cox proportional hazard models, adjusting for age, sex, race, education level, time from first to second MRI, body mass index, smoking, hypertension, diabetes mellitus, and coronary heart disease.

RESULTS

At the second brain MRI (mean age 72), the distribution of the combined measure was 37% WMH grade <2 and no lacune; 57% WMH grade ≥2 or lacune; and 6% WMH grade ≥2 and lacune. No progression in the combined measures was observed in 38% of participants, 57% showed mild progression and 5% showed moderate progression. Sixty-four incident strokes occurred during the follow-up period. Compared with no change in the combined measure, moderate progression of microvascular brain disease was significantly associated with higher risk of stroke (adjusted hazard ratio, 3.00 [95% CI, 1.30-6.94]).

CONCLUSIONS

Progression of microvascular brain disease, manifesting as both new lacunes and increase in WMHs grade, is related to substantial increase in long-term risk of stroke.

Detrimental effect of systemic vascular risk factors on brain hemodynamic function assessed with MRI

Background and purpose Vascular risk factors have been associated with decreased cerebral blood flow (CBF) but this is etiologically nonspecific and may result from vascular insufficiency or a response to decreased brain metabolic activity. We apply new MRI techniques to measure oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen consumption (CMRO₂), hypothesizing that decreased CBF related to these vascular risk factors will be associated with increased OEF, confirming a primary vascular insufficiency. Methods 3T MRI was obtained on 70 community-based participants in this IRB-approved study with informed consent, with previous assessment of systolic blood pressure, hypertension medication, elevated serum triglycerides, low serum HDL, and diabetes mellitus. CBF was measured using phase contrast adjusted for brain volume (ml/100 g/min), OEF (%) was obtained from T2-Relaxation-Under-Spin-Tagging (TRUST), and CMRO₂ (μmol/100 g/min) was derived using the Fick principle. Stepwise linear regression identified optimal predictors of CBF with age, sex, and hematocrit included for adjustment. This predictive model was then evaluated against OEF and CMRO₂. Results Hypertriglyceridemia was associated with low CBF and high OEF. High systolic blood pressure was associated with high CBF and low OEF, which was primarily attributable to those with pressures above 160 mmHg. Neither risk factor was associated with significant differences in cerebral metabolic rate. Conclusion Low CBF related to hypertriglyceridemia was accompanied by high OEF with no significant difference in CMRO₂, confirming subclinical vascular insufficiency. High CBF related to high systolic blood pressure likely reflected limitations of autoregulation at higher blood pressures.