MRA and CEMRA images of case 1 (A-D) and case 2 (E-H). No abnormality was observed in the internal carotid arteries. A, E) Angiograms show tortuosity of the basilar artery. B, F) CEMRA images show bilateral tortuosity in the V1-V2 segment of the vertebral artery, and bilateral spiral twisting in the V4 segments of the vertebral arteries without obvious stenosis. C, G) Cross-sectional images of MRA show that the left and right vertebral arteries lie adjacent to each other. D, H) Acute brain infarction is not observed.