Dual origin of the vertebral artery--case report.

A 27-year-old female presented with dual origin of the left vertebral artery. Twenty-six cases of this rare congenital vascular anomaly have been reported. In general, the medial leg of the dual origin of the vertebral artery enters a higher transverse foramen (usually the fifth or less frequently the fourth) than the lateral leg, which usually enters the sixth. Exceptions to this rule occur when the medial and lateral legs of the right vertebral artery enter the right seventh and sixth transverse foramina, respectively. This congenital vascular anomaly has diagnostic and therapeutic implications in any intervention involving the proximal vertebral artery.