Conversion of Ischemic Brain Tissue Into Infarction Increases With Age

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Abstract
Background and Purpose— Brain regions normal on diffusion-weighted imaging (DWI) but abnormal on mean transit time (MTT) maps represent tissue at risk of infarction, yet the fate of these regions is quite variable. The imperfect correlation between tissue outcome and initial imaging parameters suggests that each patient’s brain may have different susceptibility to ischemic stress. We hypothesize that age is a marker for tissue susceptibility to ischemia and thus plays a role in determining tissue outcome in human stroke. Methods— Sixty patients with acute ischemic stroke and a region of DWI/MTT mismatch that was >20% of the DWI volume were included. All patients were scanned twice, within 12 hours of symptom onset and on day 5 or later. The percentage mismatch lost (PML) was calculated as percentage of initial DWI/MTT mismatch volume that was infarcted on the follow-up MRI. The statistical analysis explored relationships among the covariates age, Trial of Org 10172 in Acute Stroke Treatment (TOAST) subtypes, time-to-MRI, and initial DWI, MTT volume, mean arterial blood pressure and blood glucose level at admission, and previous history of hypertension and diabetes mellitus. Results— Univariate comparisons showed that age ( P =0.003), hypertension ( P =0.009), and diabetes mellitus ( P =0.0002) were significantly associated with PML. Regression analyses showed age to be a significant covariate ( P =0.02). The regression model predicted a change in PML of ≈0.65% per year. The adjusted proportion of variance ( R 2 ) in PML that could be explained by age alone was 14%. Conclusion— Age-dependent increase in conversion of ischemic tissue into infarction suggests that age is a biological marker for the variability in tissue outcome in acute human stroke.

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