Single extracranial-intracranial duplication of the vertebral artery

Duplication or fenestration of the vertebral artery is an unusual vascular variation previously described as present either at the extracranial segment (atlantoaxial level) or at the intracranial segment of the artery. This report describes such a duplication that extended from the extracranial to the intracranial segment and was revealed by angiography. The embryologic genesis and potential clinical significance of this condition are discussed.