Variations in the origin and course of the extracranial vertebral artery on multidetector computed tomography angiography

Background: Variations in the origin of vertebral arteries (VA) and its entrance level into the transverse foramen are common and important when planning neck and cervical spine interventions. Objectives: The aim of this study was to investigate the prevalence of anatomical variations in the origin of vertebral arteries, and anomalous course of the extracranial vertebral artery using dual energy CT angiography. Patients and Methods: Retrospectively, we reviewed head and neck dual energy computed tomography (DECT) angiographies of 1218 consecutive patients during 2010-2014. The images were evaluated with exceptional attention to the origin of VA and its level of entrance into and exit out of the transverse foramen of the cervical spine, specific variations of VA including fenestration and intradural course of C1-C2 VA. Results: We found a rare case of double origin of left VA with bifid origins (one from the aortic arch and the other from the left subclavian artery) and entering the transverse foramen at C6 and C5 levels. The majority of left VA (1173/1219, 96.2%) originated from the left subclavian artery. Most of them (1159/1173, 98.8%) entered the C6 transverse foramen. Forty-six of left VA (46/1219, 3.8 %) originated from the aortic arch and thirty-seven (80.4%) of them entered the C5 transverse foramen. When the left VA arose from the aorta, there was a significant higher rate of anomalous entrance level (C4 or C5) to normal C6 entrance level (P < 0.001). The majority of right VA (1209/1218, 99.3%) originated from the right subclavian artery. Eight (0.7 %) of right VA arose from the aberrant right subclavian artery (ARSA). One rare case of right VA from right common carotid artery (CCA) entered the transverse foramen at C4 level with coexisting ARSA. Five cases had atlanto-axial fenestration of the VAs and five cases had intradural course of left C1-C2 VAs. Conclusion: The study showed anatomical variations of the VA in its origin and extracranial course. A pre-operative CT angiography is useful to identify the anomalous extracranial VA course. It reduces the risk of intra-procedure VA injury.