[Non invasive imaging of bilateral vertebral arteries agenesis].

Imaging descriptions are lacking for vertebral artery variants reported in the anatomy literature. We report thus a variant of vertebral arteries discovered incidentally in a patient admitted for aortocoronary bypass. Doppler of the supra-aortic arches revealed the absence of cervical segments of both vertebral arteries. Transcranial doppler revealed the presence of intracranial segments of these arteries that continued in a normal basilar trunk. MR-angiography performed on a 3T machine confirmed the bilateral absence of cervical segments and the presence of normal intracranial segments arising from the occipital arteries, branches of the external carotid arteries. Embryologic analysis explains this variant by an involution of cervical segments and persistence of anastomoses between the external carotid system and the vertebrobasilar system that normally regresses during fetal life. This anastomosis enables irrigation of the intracranial vertebrobasilar system by the external carotid artery. The introduction of 3T MR-angiography has enabled better and more precise detection of vascular variants without invasive angiography.