Interhemispheric Asymmetry In Mechanisms Of Large-artery Atherosclerotic Ischemic Stroke

Background and Purpose: Large-artery atherosclerosis (LAA) is one of the main causes of ischemic stroke. Among the types of anterior circulation atherosclerosis, common carotid artery (CCA), internal carotid artery (ICA) and middle cerebral artery (MCA) are frequently seen. Infarct lesions were manually divided into four patterns based on the diffusion-weighted imaging (DWI) sequence including several disseminated small infarcts, territory infarcts, perforator infarcts, watershed infarcts. Possible corresponding mechanisms of LAA ischemic stroke include artery-to-artery embolism, parent artery plaque or thrombus occluding penetrating artery, hypoperfusion/impaired clearance of emboliand mixed mechanisms. It is seemingly plausible that the mechanisms of left and right atherosclerotic stenosis resulting in ischemic stroke should be similar, but prior research has found that ischemic stroke was more often diagnosed in the left hemisphere (LH) than in the right hemisphere (RH). In this study, we compared the sites of large arterial stenosis and topographic patterns of infarcts among patients presenting with LAA ischemic stroke within the anterior circulation territory of the LH and RH to infer whether the mechanisms of stroke differ between the two hemispheres.Methods: We retrospectively analyzed consecutive patients admitted to Chinese PLA General Hospital between January 2008 and May 2016 who were confirmed to have acute unilateral ischemic infarcts within the anterior circulation territory on DWI within 2 weeks from onset and culprit vascular stenosis on vascular imaging. They were divided into two groups: left hemisphere stroke(LHS) group and right hemisphere stroke(RHS) group. We compared the patients' demographics, ischemic stroke risk factors, sites of stenosis within the anterior circulation and mechanisms of stroke (according to the Chinese Ischemic Stroke Subclassification [CISS] criteria) between two groups. We also investigated whether the stroke mechanisms were related to the sites of stenosis.Results:(1).In this study, there were 339 (50.5%) LHSpatients and 332 (49.5%) RHSpatients.There was no significant difference in gender, age, BMI, ischemic stroke risk factors or thesites of stenosis based on stroke side.(2). The CISS subtype distribution in those 339 LIIS patients was artery-to-artery embolism in 208 (61.36%), parent artery plaque or thrombus occluding penetrating artery in 58 (17. 11 %), and hypoperfusion/impaired clearance of emboli in 156 (46. 02%). The CISS subtype distribution in those 332 RHS patients was artery-to-artery embolism in 174 (52. 41 %) , parent artery plaque or thrombus occluding penetrating artery in 50 (15. 06%),and hypoperfusion/impaired clearance of emboli in 203 (61. 14%). The stroke mechanism(according to CISS criteria) were asymmetrically distributed between LHS and RHS. Artery-to-artery embolic mechanism were observed more frequently in patients with LHS than in those with RHS (p=0.019) whereas the mechanism of hypoperfusion/impaired clearance of emboli appeared to be more common on the right than on the left (p=0.000).(3). The watershed infarction subtype distribution in those 156 LHS patients was anterior watershed pattern in 49 (31.41%), internal watershed pattern in 126 (80.77%), and posterior watershed pattern in 92 (58.97%). The watershed infarction subtype distribution in those 203 RHS patients was anterior watershed pattern in 85 (41.87%), internal watershed pattern in 176 (86.70%), and posterior watershed pattern in 123 (60.59%). The distribution of anterior watershed pattern was more frequently in RH than in LH (p=0.042), while internal and posterior watershed pattern had no significant difference between the two hemispheres.(4). 120 cases of CA stenosis patients and 116 cases of MCA stenosis patients were found in watershed infarction patients. Among those CA stenosis patients, there were 62 (51.67%)anterior watershed infarction patients, 94 (78.33%) internal watershed infarction patients and 55 (45.83%) posterior watershed infarction patients.Whileamong those MCA stenosis patients, there were 29 (25.66%) anterior watershed infarction patients, 86 (76.11%) internal watershed infarction patients and 61(53.98%)posterior watershed infarction patients. The incidence of anterior watershed infarction in CA group (62,61.67%) was more often than MCAGroup(29,25.66%) (p=0.000), but this asymmetric distribution was not found between LH andRH across other subtypes of watershed infarction.Conclusions: The incidence of territory patterns was significantly higher in the LH than in the RH, whereas watershed patterns appeared to be more frequent in the RH than in the LH.It may be reasonable to hypothesize that an artery-to-artery embolic mechanism may play a more crucial role in the pathogenesis of LHS, while a mechanism of hypoperfusion/impaired clearance of emboli is likely to be more important in the pathogenesis of RIHS according to the CISS criteria.In the future, more studies should be conducted to identify factors underlying the interhemispheric asymmetry of stroke mechanisms such as collateral circulation and cerebral blood perfusion. Understanding these specific pathways could contribute to the prevention of stroke in primary care.