Fig. 1 Preoperative, contrast-enhanced, 3-dimensional, magnetic resonance angiogram (lateral view) reveals severe hypoplasia of the transverse aortic arch (arrow) between the origins of the left common carotid and left subclavian arteries (interrupted aortic arch, type B). Extensive collateral vessels are evident in the paraspinal region (arrowheads) and involve the vertebrobasilar system (asterisk). The dark gray areas show vessels with antegrade flow, and the light gray areas denote those with retrograde flow.