Mapping of Anatomic Variants of the Proximal Vertebral Artery in Relation to Embryology.

Abstract

Variations in the origins and courses of the vertebral arteries are relatively rare but may be clinically meaningful. We hypothesize a relationship between variant origins of the vertebral arteries and their levels of entry to the foramina transversaria. In this retrospective study of CT angiograms, we document the frequency and types of vertebral artery variants, correlating origins with levels of entry to the foramina transversaria. Vertebral artery variants were observed in 18.7% of a sample of 460 CT angiograms of the neck. Right-sided variants were less common than left (44.2% versus 68.6%, with 12.8% bilateral) and more common than previously thought. The most common variant on both sides was a variant origin proximal to the normal vertebral artery origin and entry at C5. Most right vertebral arteries originating within 2 cm of the origin of the right subclavian artery and left vertebral arteries originating between the left common carotid and subclavian arteries were "high-entry" variants. Most "low-entry" variants, entering at C7, took origin from the arch just distal to the left subclavian artery or at a common origin with the costocervical trunk. Multiple origins or accessory vertebral arteries were also described, and each moiety followed the same rules described for single origins. A map of vertebral artery origins mirrored the map of aortic arch embryology. Vertebral artery variants follow certain well-defined patterns that correlate with the embryology of the aortic arch and great vessels.