https://www.youtube.com/watch?v=DwaVpLip3G4
V2 segment
- entry of VA higher than C6 or through the C7 foramen transversarium
- loops (medial or lateral)
- medial loops (at disc or vertebral body level)
V3 segment (divided into three parts)
V31 – High riding vertebral artery – too high, too posterior or too medial
V32 – VA branches below the C1 arch (extracranial origin of PICA, VA coursing below the C1 arch (persistent first intersegmental artery), or a fenestrated VA)
V33 – Ponticulus ponticus, abnormal courses associated with occipitalised atlas