| ABSTRACT0bjective: Intracranial atherosclerotic disease is a major cause of ischemic stroke worldwide, especially in Asia. The possible stroke mechanisms in intracranial artery atherosclerosis are variable including thrombosis obstructing single or multiple perforating arteries, arterial emboli formation disseminating into the distal branches, and hemodynamic compromise in the watershed area. But they have the same pathologic change: unstable atherosclerotic plaque. There is growing awareness that stenosis severity alone has limited value in predicting plaque stability and small atherosclerotic plaques can be vulnerable plaques too. High resolution magnetic resonance imaging(HR MRI) is able to reveal intracranial vessel wall pathology. This imaging technique can detect intracranial arterial plaques even when luminal angiography reveals no abnormalities. It has been reported that HRMRI is able to identify the components and structure of plaques and the remodeling ratio of narrowed artery. So HRMRI is able to identify the vulnerability of plaques as well as permit more accurate stroke sub-typing and the risk of stroke recurrence. The aim of this study was to accurate stroke sub-typing in patients with strokes of unknown origin and compare images of the vessel wall between asymptomatic atherosclerotic plaques and symptomatic atherosclerotic plaques of different mechanisms of stroke using HRMRI.Methods: 1 Study populations: 1.1 Confirmed cases of symptomatic intracranial atherosclerotic disease diagnosed by transcranial Doppler(TCD)/MRA/MRI, based on the TOAST classification. 1.2 Patients who were diagnosed as suspected artery-to-artery embolism: Imaging shows small cortical infarcts in the area supplied by the relevant intracranial artery, while the relevant intracranial artery was normal disclosed by conventional imaging. And there was no evidence of potential cardiac-origin embolic cause, other possible causes have also been excluded. 1.3 Patients who had isolated infarct in the territory of penetrating artery but the relevant parent artery was normal disclosed by conventional imaging. 1.4 Patients whose diagnosis was asymptomatic intracranial atherosclerotic disease: There was intracranial atherosclerotic stenosis diagnosed by transcranial Doppler(TCD)/MRA, while there was no infarction involving the relevant intracranial territory. 2 Study methods: 2.1 Patients of symptomatic intracranial atherosclerotic disease were categorized into three groups according to the diffusion-weighted images: 2.1.1 Artery-to-artery embolism group: Small cortical infarcts or a single territory infarct in the area supplied by the relevant intracranial artery atherosclerosis. 2.1.2 Hypoperfusion or multiple mechanism group: The acute infarcts occur in the borderzone area with or without acute cortical or territory infarcts related to this diseased artery. 2.1.3 Parent artery(plaque or thrombus) occluding penetrating artery group: Acute or previous infarct occurs in penetrating artery territory. Then 3-T high-resolution magnetic resonance imaging(HR MRI) was performed in the relevant intracranial artery. We determined the area of the plaque, plaque irregularity, plaque signal intensity, degree of stenosis, remodeling ratio, outward and inward remodeling, and % wall volume. And then compare images of the vessel wall between asymptomatic atherosclerotic plaques and symptomatic atherosclerotic plaques of different mechanisms of stroke. 2.2 All patients who were diagnosed as suspected artery-to-artery embolism underwent the HR MRI to determine the presence of atherosclerotic plaques within the relevant intracranial artery. 2.3 All patients who had isolated infarct in the territory of penetrating artery but the relevant parent artery was normal disclosed by conventional imaging underwent the HR MRI to determine the presence of atherosclerotic plaques within the relevant parent artery. And to evaluate the value of HR MRI in accurately stroke sub-typing in patients with isolated infarct in the territory of penetrating artery. 3 Statistical analysis:Categorical variables were presented as absolute frequencies, and continuous variables were expressed as mean(standard deviation). We compared the group of asymptomatic intracranial atherosclerotic disease with the group of symptomatic intracranial atherosclerotic disease by using the Fisher exact test for categorical variables and by using the One- Way ANOVA test for continuous variables. After a significant effect has been found we went further to determine which pairwise groups had significant differences by using the Bonferroni test for categorical variables. Significance was set at the 2-tailed P<0.05 and calibration significant level was 0.0083. All the statistical analyses were performed using SPSS version 13(SPSS Inc).Results: There were a total of 72 patients with infarction and 16 patients of asymptomatic intracranial atherosclerotic disease who had undergone high-resolution MRI. However, patients with poor image quality and patients who were hard to clear relevant intracranial artery or lack of proper reference plane were excluded. Finally, 61 patients were enrolled for analysis, including 46 patients whose diagnosis was symptomatic intracranial atherosclerotic disease, 5 patients whose diagnosis was suspected artery-to-artery embolism and 10 patients who had perforator artery infarction but had no parent artery stenosis. 9 patients of asymptomatic intracranial atherosclerotic disease served as control group. 46 patients whose diagnosis was symptomatic intracranial atherosclerotic disease were divided into 3 groups: artery-to-artery embolism group: 19 patients; hypoperfusion or multiple mechanism group: 7 patients and Parent artery(plaque or thrombus) occluding penetrating artery group: 20 patients. There was no significant difference in the clinical and demographic data between the patients of different mechanisms of intracranial atherosclerotic stroke.Compared with the control group, outward remodeling of the stenotic area in the group of artery-to-artery embolism was significantly higher(P<0.001). But inward remodeling of the stenotic area in the asymptomatic group was significantly higher than that in the group of artery-to-artery embolism(P = 0.001). The plaques of the group of the parent artery(plaque or thrombus) occluding penetrating artery were more frequently located close to perforators arterial openings(P = 0.002) than the control group. There was no significant difference in the area of the plaque, plaque irregularity, plaque signal intensity, degree of stenosis and % wall volume between the patients of different mechanisms of intracranial atherosclerotic stroke and control group.After HR MRI was performed in the relevant intracranial artery of patients whose diagnosis was suspected artery-to-artery embolism, atherosclerotic plaque was found in all of the relevant intracranial artery.All the 10 patients who had isolated infarct in the territory of penetrating artery but the relevant parent artery was normal disclosed by conventional imaging underwent the HR MRI. 5 of the Patients were diagnosed as parent artery(plaque or thrombus) occluding penetrating artery.Conclusions: Outward remodeling of the stenotic area in symptomatic group was significantly higher than that seen in the asymptomatic group, and the reverse was true for inward remodeling of the stenotic area. And compared with control group, the plaques of the symptomatic group were more frequently located close to perforators arterial openings. Indicate that outward remodeling of the stenotic area and plaques located close to perforators arterial openings are the characteristic of unstable plaques, which play a key role in predicting stroke risk. This novel imaging technique HR MRI has higher sensitivity than MRA, especially atherosclerosis in early stage without significant lumen stenosis. It can be used to accurate stroke sub-typing in patients with strokes of unknown origin. |
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