Distal versus Proximal Middle Cerebral Artery Occlusion: Different Mechanisms

<b><i>Background:</i></b> Clinical and radiological characteristics of middle cerebral artery (MCA) infarction may differ according to the location of occlusion. <b><i>Objectives:</i></b> We investigated the difference between proximal and distal symptomatic MCA occlusion (MCAO) in patients with ischemic stroke. The factors associated with the imaging characteristics were also analyzed. <b><i>Methods:</i></b> Patients with ischemic stroke due to MCAO were consecutively enrolled. The location of MCAO was determined by the ratio of the length of the ipsilesional MCA to that of the contralateral MCA and dichotomized to proximal and distal MCAO. Clinical and radiological characteristics were compared between patients with proximal and distal MCAO. Factors associated with the basal ganglia (BG) involvement, hemorrhagic transformation (HT), and neurological change during admission were investigated. <b><i>Results:</i></b> Among 181 included patients, MCAO location showed a bimodal peak (at the proximal [<i>n</i> = 99] and distal MCA [<i>n</i> = 82]). Proximal MCAO was more frequently associated with hyperlipidemia and large artery atherosclerosis, whereas distal MCAO was more frequently associated with hypertension, atrial fibrillation, and cardioembolic stroke. BG involvement was similar between the 2 groups (48 vs. 39%; <i>p</i> = 0.21), whereas HT was more frequent in distal MCAO (10 vs. 23%; <i>p</i> = 0.02). Among patients with proximal MCAO, hyperintense vessel sign was less frequently observed in those with a BG involvement than those without (38 vs. 60%; <i>p</i> = 0.03). Among those without BG involvement, the presence of HT was very low and similar between patients with proximal and distal MCAOs (1.9 vs. 2.0%). However, in patients with BG involvement, HT was more frequently observed in those with distal MCAO than in those with proximal MCAO (54.8 vs. 15.7%; <i>p</i> &#x3c; 0.001). The presence of hyperintense vessel sign (OR 0.172, 95% CI 0.051–0.586; <i>p</i> = 0.005) and distal MCAO (OR 0.200, 95% CI 0.059–0.683; <i>p</i> = 0.011) was independently associated with improvement during admission. <b><i>Conclusion:</i></b> Proximal MCAO is more frequently associated with atherosclerosis, whereas distal MCAO is more frequently associated with cardioembolism. In proximal MCAO, the status of collateral flow presented by hyperintense vessel sign may affect the involvement of BG. In distal MCAO, distal migration of the embolus, which first impacted at the proximal MCA causing BG ischemia, may explain the high rate of HT by reperfusion injury. Hyperintense vessel sign and distal MCAO were independently associated with neurological improvement during admission.