Diffusion- and perfusion-weighted magnetic resonance imaging in patients with acute ischemic stroke: can diffusion/perfusion mismatch predict outcome?

摘要

Introduction: Stroke is the third leading cause of death, and is the leading cause of disabilities worldwide. Although stroke may result from localized cerebral ischemia, intracerebral hemorrhage, subarachnoid hemorrhage or venous sinus thrombosis, ischemic stroke is the most frequently cause of the total cases. In ischemic stroke, occlusion of the MCA or its branches accounts for more than 3/4 of infarcts and two thirds of all first strokes. The main mechanisms causing ischemic strokes are embolism and arterial thromboembolism. No matter what the mechanism an ischemic stroke is, they eventually lead to a focal reduction of perfusion in the brain. In the hyperacute stage the recognition of the ischemia using both clinical assessment and routine neuroimaging technique implies some uncertainties, which in turn makes it difficult to predict the outcome, either to improve or to reverse spontaneously, to persist or worsen. The concept of diffusion/perfusion mismatch attracted great attention since it may represent the tissue at risk or at least an index of penumbra. Our interest was to investigate whether the hemodynamic parameters had correlation with clinical severity and if they were useful for prediction of outcome in the mismatch region. Since diffusion/perfusion mismatch was recognized as a simple and feasible means to identify the ischemic penumbra, we evaluated the hemodynamic parameters in acute stroke patients and compared these parameter to the stroke scale NIHSS and to the outcome score MRS to investigate our hypothesis.Materials and Methods: 35 acute stroke patients (male:female=20:15, age: 61.3±15.2 years) who met the study inclusion and exclusion criteria were selected. Significant cerebrovascular risk factors were recorded in 27 patients. The NIHSS assessment was immediately performed at the patients’ admission by a neurologist. Functional outcome was measured on the day of hospital discharge following MRS. Routine MRI sequences and DWI and PWI (dynamic susceptibility contrast-enhanced [DSC] imaging) were employed in our patients study. The perfusion maps were processed with MEDx® and the parameters were obtained by identifying ROIs on both ischemic core and mismatch region, and the normal mirror region. Relative values of the hemodynamic perfusion parameters were used in the evaluation. Statistic treatment was used to test the significance of the result.Results: The NIHSS score ranged from 0 to 19 (10.2±4.4) and the outcome MRS scale ranged from 0 to 6 (mean: 3.23). Between the good outcome group (MRS 0 to 3) and the poor outcome group (MRS 4 to 6), time to scan, type of treatment, DW/PW volume ratio, and age and female/male ratio did not show significant differences. In ischemic core: rCBF showed a remarkable decrease in all patients on average by 59.3±33.7% (range: 23.2 - 97.4%). rCBV decreased in 29 patients by 41.7±23.7% (range 19.6 - 55.6%), while 6 patients showed an increase of rCBV by 60.4±57.1% (range 0.7 -139%). The mean rCBV change of the entire group was 26.3±52.5%. MTT, TTP and T0 prolonged for 4.7 (SD=15.1), 2.8 (SD=12.9) and 0.5 (SD=10.4) seconds, respectively.In mismatch region: rCBF decreased in 15 patients by 26.2±19.9% (range: 5.3-58.4%) and increased in 20 patients by 35±23.2% (range: 6.8–74.4%). The change of the rCBF of the whole patients group was 5.8±38.4%. rCBV decreased in 7 patients by 14.7±16.5% (range: 0.8-44.5%) and increased in 28 patients by 39.5±36% (range: 2.2-91.1%). The mean change of the rCBV of the whole group was 19.9±31.2%. The mean value of MTT, TTP and T0 prolonged for 2.7 (SD=8.5), 3.2 (SD=5.2) and 1.3 (SD=4.2) seconds respectively.In both core and mismatch region, rCBF showed statistically significant regression to MRS. The more the rCBF decreased the higher the MRS (poor outcome) was. Also, the MTT delay in the core region was significantly related to MRS. TTP delay, in both core and mismatch region, was related to both NIHSS and MRS significantly. No statistic significance was found comparing CBV and T0 in relation with NIHSS or MRS. Conclusion: The hemodynamic parameters derived from perfusion MR imaging may be helpful adjunct to predict the outcome and severity in acute stroke patients. In mismatch region, the rCBF and TTP are predictive for the stroke outcome.