Background: To determine the role of small vertebrobasilar artery (SVBA) in patients with posterior circulation stroke (PCS), we evaluated the ischemic patterns, collateral features, and stroke mechanisms in PCS patients with SVBA.
Methods: Ischemic findings on magnetic resonance (MR) imaging were correlated with 3D time-of-flight/contrast-enhanced MR angiography and/or catheter angiography in 18 patients (mean age, 68.0+/-11.8 years; 9 males). SVBA (lumen diameter of <3 mm) was compared with stenotic normal-sized VBA (NVBA) in 14 PCS patients.
Results: Ischemic lesions were predominantly observed in the cerebellum and/or medulla (vertebral artery (VA) territory). All subjects had fetal posterior circulation (FPC) from the internal carotid artery to the posterior cerebral artery. Sixteen patients (88.9%) had distal or diffuse VA stenosis/occlusion. In 14 patients (77.8%), long circumferential artery (LCA) was prominently observed. In atherothrombotic patients, infratentorial PCS might occur following artery-to-artery embolism from the low-flowed or stenotic VA to LCA. Ischemic patterns between subjects with and without VA disease were almost similar. As the degree of VA disease increased, the frequency of LCA prominence showed an increased tendency (P=0.003). Relatively small, scattered infarcts were observed in patients with SVBA than in those with stenotic NVBA.
Conclusions: FPC does not protect against infratentorial PCS. Regardless of extensive arterial lesions, relatively small infarcts may be due to previously established collaterals from the LCA, which could compensate for the defects in the infratentorial area.