Type I proatlantal artery with bilateral absence of the external carotid arteries.

During color Doppler examination of a 41-year-old man who presented with vertigo, a right vertebral artery could not be found. Both MR angiography and digital subtraction angiography revealed a large anastomotic vessel between the right internal carotid and vertebral artery. It was thought to be type I proatlantal artery. Furthermore, the external carotid arteries were bilaterally absent. Although each vascular anomaly mentioned above is rare, it even more rare for these variations to occur simultaneously. Copyright American Society of Neuroradiology