MCA stenosis was significantly associated with CSO-EPVS (no stenosis vs mild or moderate stenosis: 95%CI [0.954, 4.473], P=0.000; no stenosis vs severe stenosis or occlusion: 95%CI [4.419, 9.586], P=0.000). Cerebral hemisphere volume was correlated with CSO-EPVS (no stenosis vs mild or moderate stenosis: 95%CI [-0.824, 0.414], P=0.047; no stenosis vs severe stenosis or occlusion: 95%CI [-1.051, 4.431], P=0.018), but there was no significant correlation between MCA stenosis and the hemisphere volume (no stenosis vs mild or moderate stenosis: 95%CI [-0.097, 0.123], P=0.434; no stenosis vs. severe stenosis or occlusion: 95%CI [-1.012, 1.210], P=0.403). Mediating variable analysis showed that hemisphere volume had no mediating effect in the correlation between the MCA stenosis and CSO-EPVS (no stenosis vs mild or moderate stenosis: 95%CI [-0.039, 0.329], P=0.910; no stenosis vs severe stenosis or occlusion: 95%CI [-0.118, 0.106], P=0.350).