Ultrasound diagnostics of the vertebrobasilar system.

Despite the fact that ischemic stroke in the vertebrobasilar system (VBS) is significantly less frequent than in the carotid system, abnormalities found in Doppler and duplex examinations are about as prevalent in the VBS as in the carotid system. Because of the potentially severe clinical deficits associated with stroke of the VBS and the increased risk for stroke under conditions, such as underlying symptomatic vertebrobasilar stenosis and general anesthesia, it is highly desirable to have reliable methods available to identify pathological changes of the VBS. Furthermore, because the VBS via the circle of Willis can play a significant role as collateral blood supply system when vessels of the anterior circulation have been compromised, the knowledge of the VBS is necessary to estimate the overall integrity of the remaining blood flow to the brain.