Arteries get confused: an arch variation.

We present a case of an arch anomaly in a 54-year-old female who was admitted to our hospital for magnetic resonance angiography (MRA) to evaluate her right-sided numbness. MRA revealed a truncus bicaroticus, right common carotid artery (CCA) originating right vertebral artery, right subclavian artery arising as the final branch of the descending aortic arch and arch originating left vertebral artery. The possible embryologic mechanism and clinical importance of this previously unreported variant are reviewed.