Origin of the right vertebral artery from the left side of the aortic arch proximal to the origin of the left subclavian artery.

The right vertebral artery most commonly originates from the right subclavian artery. There are a variety of anomalous origins of the right vertebral artery described throughout the literature ( 114); however, in most cases the artery arises from a vessel on the right side of the aortic arch. There have only been three reports of the right vertebral artery crossing over from an origin on the left side of the aortic arch, and in all cases the origin was distal to the origin of the left subclavian artery (1-3). We report a case in which the right vertebral artery originates from the left side of the arch and crosses to the right, but the origin is proximal to the left subclavian artery (Figs. 1, 2, and 3). An embryologic derivation is described that can adequately account for each variant. Understanding the variations in anatomy of the right vertebral artery can help avoid problems when a variant is present during cerebral angiography or a surgical procedure.