Posterior circulation ischemia in patients with fetal-type circle of Willis and hypoplastic vertebrobasilar system

Little attention has been given to the fetal-type posterior circle of Willis (FTP) in the literature; also symptomatic basilar artery (BA) hypoplasia has been rarely reported. We aimed to illustrate that the association of a hypoplastic vertebrobasilar system (VBS) with the FTP may lead to posterior circulation ischemia. Magnetic resonance imaging and three-dimensional time-of-flight magnetic resonance angiography were performed in 88 consecutive patients with ischemic stroke or TIA in the VBS. Thirteen patients were identified with either stroke or TIA in the context of a hypoplastic VBS and a fetal origin of the posterior cerebral arteries. All patients had unilateral or bilateral FTP, hypoplastic BA and at least one hypoplastic vertebral artery. Transcranial color-coded duplex revealed decreased flow velocity and increased pulsatility index along the BA. A hypoplastic VBS may be accompanied by the FTP and its simultaneous occurrence can predispose to ischemic events in the posterior circulation.