Modalities of collateral supply of cerebral circulation through the circle of Willis in stenoses and occlusions of extracranial carotid arteries.

The intracranial cerebral circulation was studied in 6 patients with bilateral ischemic lesions due to lesions of the internal carotid artery in the extracranial segment (2 significant bilateral stenosis cases; 1 case with bilateral thrombosis and 3 cases of unilateral thrombosis and significant controlateral stenosis). All the patients were males their age ranging between the 5th and 8th decades of life. In a single case, the neurological examination showed secondary left hemiplegia and recent right paresis of remittent type whereas the other 5 patients had only transient ischemic attacks with hemiparesis or transient aphasia. The lesions were revealed by duplex system echotomography (Aloka-Hellige Model SSD-630) and spectral analysis of Doppler signal (Vasoscan-Sonicaid) and were later confirmed by bilateral carotid arteriography in all patients. The intracranial circulation was also watched by noninvasive methods using the spectral analysis of the Doppler signal with pulsed wave on TC-2 64-B apparatus. As for the modalities of blood flow compensatory mechanisms by the circle of Willis, it may be noted that in none of the patients investigated did the collateral supply observe a "mathematical model".