Atypical vertebral artery: embryological explanation and implications in neck surgery

Atypical branches of the aortic arch (AA) occur frequently but are poorly explained. In an 82-year-old Caucasian male cadaver who died of coronary artery disease with severe aortic stenosis, the left vertebral artery (LVA) originated from the AA between the common carotid and subclavian arteries. The prevertebral part of LVA was narrower and entered the C5 transverse foramen. The right vertebral artery (RVA) from the right subclavian was wider than LVA suggesting compensation to the cerebral circulation. An unusual LVA may be asymptomatic; however, it is important in neck and supraaortic arch surgery and in non-invasive neck procedures. Vertebral arteries (VAs) are formed by development of longitudinal anastomoses linking the cervical intersegmental arteries, which regress except the seventh that becomes the proximal subclavian artery, the point of origin of the adult VA. Persistence of the 6th dorsal intersegmental artery might account for LVA arising from AA proximal to the subclavian artery.