[Transcranial Doppler: first results of exploration of the circle of Willis]

Over a two year period, 500 intracranial examinations were performed to explore the arteries at the base of the skull (middle, anterior and posterior cerebral) as well as the basilar artery. Exploration of the carotid siphons by the transorbital route is not systematic but used when approach to the vessels by the temporal windows is impossible. The transcranial Doppler examination is particularly indicated in the following circumstances: (1) In patients presenting a tight stenosis on the extracranial internal carotid artery (50 cases). The intracranial effects of extracranial lesions depend on the degree of obstruction and blood supply values at the level of the circle of Willis. (2) During cerebral vascular accidents without extracranial lesions in order to detect possible intracranial involvement (15 cases). Occlusions (5 cases) raised more diagnostic problems than did tight stenoses. (3) In meningeal haemorrhages, in which the degree of spasm can be measured, to provide elements to prognosis (8 cases). (4) In angiomas and intracranial malformations (5 cases). To a certain extent, the examination makes it possible to determine the region concerned by the fistula and, especially, to assess the effects on locoregional circulation. The main drawback of the method is the absence of a temporal window, preventing direct access to vessels at the base of the skull. Moreover, certain arteries are not easily accessible and thus not always found or at least recognized with certitude. However, reliability has improved with experience, and accurate diagnoses can now be made.