Figure 4. (A) During angiography in the neutral head position, the right vertebral artery, basilar artery, and distal branches showed good contrast enhancement. (B) During angiography with the head tilted to the left, the right vertebral artery exhibited decreased blood flow (red arrow indicates sign of compression), and the basilar artery and distal branches showed poor contrast enhancement (blue arrow indicates the contour of cervical C1). (C) In the neutral head position, CTA confirmed normal anatomy and flow pattern of the right vertebral artery (indicated by the blue arrow). (D) CTA revealed compression of the right vertebral artery by the bone margin of the axis when the head was turned to the left (indicated by the red arrow). CTA – computed tomography angiography.