Failure to visualize the left vertebral artery
AP projection of a left subclavian angiogram demonstrates the absence of the left vertebral artery. No left vertebral artery was visualized originating from the arch of the aorta, nor was there visualization from right vertebral injections. Good blood flow was present in the circle of Willis.The curvilinear artery extending cephalad is an ascending cervical branch of the thyrocervical trunk.
Great variation can be seen in the vertebral
arteries. The vertebrals are usually asymmetric with the left vertebral
being dominant in up to 75% of cases. The vertebrals can be hypoplastic,
duplicated or fenestrated. The left vertebral artery can have many
potential sites of origin. The origins include the subclavian artery
(normal), internal carotid artery, aortic arch between the common carotid
and subclavian artery, and the aortic arch distal to the subclavian
artery.