The mechanisms activated in case of occlusion of a cerebral artery are: 1) anatomical compensation; 2) cerebral self-regulation; 3) metabolic adjustments.
The anatomical compensations occur mainly through three anastomoses: 1) Willis polygon; 2) extracranial collateral arteries; 3) cortical arteries.
Moreover, in case of reduction of the perfusion pressure, the mechanism of cerebral self-regulation involves a vasodilation with a fall of peripheral resistances and consequent increase in blood flow.
Finally, when compensatory dilation is maximal, any further decrease in perfusion pressure leads to a fall in brain blood flow. The haemodynamic reserve is, therefore, exhausted: at this point the decrease in flow can be compensated only by metabolic adjustments of the brain tissue with an increase in the rate of O2 extraction.
US is a sensitive technique that can be used for the evaluation of the anatomical compensations through Willis polygon and cervical arteries in patients with obstruction of cerebral vessels, with possible important prognostic/therapeutic implications.
Franco Accorsi, MD
Member of the Order of Physician of Bologna n° 6728
I am a specialist in Medical Angiology and I am based in Bologna, Italy. Until 2008 (voluntary resignation) I worked at Maggiore Hospital in Bologna as "Dirigente Medico" in the Department of Internal Medicine and as Angiologist in the Angiology Unit with a position of "Alta Professionalità" in "Vascular Ecography and Angiology".
I am currently working in Bologna as an independent professional in the areas of angiology and vascular diagnostics.
I have been a speaker at national and international courses/congress and I have taught duplex ultrasound method in GIUV and SIUMB courses at the Maggiore Hospital, Bologna and courses of echocolor Doppler of extracranial and intracranial arteries at the Stroke Unit of S. Maria Nuova Hospital, Reggio Emilia.