[Observations on the vertebro-basilar system studied by ultrasound].

Vertebro-basilar circulation is complex because conditioned by several factors. Ultrasounds allow the study of many of its aspect, both hemodynamic and anatomical. Data were obtained from the examination of 50,000 patients over 25 years, of which the last 1,000 patients were examined by means of transcranial Doppler, duplex scanner color and power. 40% of these patients were found normal, 20% only had arterial thickening, 26% various types of stenosis, 10.6% subclavian steal, 14% short vertigo. The basilar artery (BA) flow (230 ml/min +/- 40) is similar to that of the internal carotid (245 ml/min +/- 50). In elderly patients, the absence of a posterior communicating artery (28%) or of both arteries (13%) is more frequent than the absence of the anterior communicating artery (7%). In normal patients decubitus variations do not modify the BA flow. In patients with vertigo due to decubitus variations, BA flow velocity increases from 20% to 40% during vertigo. Subclavian steal completely modifies the hemodynamics of vertebral arteries, while in the BA it can vary in part or completely. In conclusion, vertebral hemodynamics is different from BA hemodynamics. BA must be considered as one side of the Willis' polygon because it is an anastomosis between the vertebral arteries and is a "hemodynamic damper" between intracranial and extracranial circulation.