On left side there are 2 separate origins of the vertebral artery from the corresponding subclavian, the duplicated vessels join together before continuing as one vessel in the foramina transversaria. Duplication is thought to represent failure of controlled regression of 2nd intersegmental arteries and a segment of the primitive dorsal aorta. This finding is discovered on a 2D TOF Non contrast neck MR angiogram as an incidental finding without obvious clinical implications.
Duplication and fenestration of the extra cranial vertebral artery are considered as a rare developmental anomalies. In many case reports, the terms fenestration and duplication have been used incorrectly and interchangeably. Duplication should be strictly applied to a vertebral artery that has 2 origins and a variable course with fusion again in the neck itself. In contrast, fenestration represents a vessel with a single origin, anywhere along its course the main trunk divides into 2 parallel segments that may lie within or outside of the vertebral canal but and unite again.
Schematic representation of the embryology of the duplication of the bilateral vertebral arteries. Modified from Goddard et al.
The embryogenesis of the vertebral artery begins at approximately 32 days and is completed by 40 days, between the 12.5- and 16-mm stages.1,13 The vertebral artery is formed from fusion of the longitudinal anastomoses that link cervical intersegmental arteries, which branch off the primitive paired dorsal aorta. The intersegmental arteries eventually regress, except for the seventh vessel, which forms the proximal portion of the subclavian artery, including the point of origin of the vertebral artery. As their connections to the primitive dorsal aorta disappear, the vertebral artery is formed and takes on the appearance of a beaded anastomotic chain with a tortuous course. The basilar artery is formed by the fusion of the 2 primitive vertebral arteries. Sim et al1 state that a portion of the primitive dorsal aorta may not regress along with 2 intersegmental arteries that connect to the vertebral artery. It is believed that this arrangement may give rise to vertebral artery duplication or double origin to that vessel.
In this case duplication of proximal portion of left vertebral artery may be explained by persistence of a portion of the primitive dorsal aorta segment along with lack of regression of the fifth and sixth intersegmental arteries on left side.
Duplications and fenestrations of the extracranial course of the vertebral artery are rarely reported in the literature and are seen as incidental findings in autopsy series, angiographic studies, recently in MR angiography (MRA) studies. The presence of duplication or fenestration of the vertebrobasilar or carotid system may or may not be associated with specific symptoms or other pathologies but may influence the choice or route of endovascular procedure and should be mentioned in report.
Reference: American Society of Neuroradiology.