Figure 3. (A) During angiography in the neutral head position, the left vertebral artery, basilar artery, and distal branches showed good contrast enhancement. (B) During angiography with the head tilted to the right, the left vertebral artery exhibits slow blood flow. A compressed indentation was observed in the V3 segment of the vertebral artery (indicated by the red arrow). The basilar artery and distal branches showed poor contrast enhancement. (C) In the neutral head position, CTA confirmed a normal anatomy and flow pattern of the left vertebral artery (indicated by the blue arrow). (D) CTA revealed that the left vertebral artery was compressed by the bone margin of the axis when the head was turned to the right (indicated by the red arrow). CTA – computed tomography angiography.