Extra and intracranial compensation for steno-occlusions of cerebral vessels. The role of US.

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.

 

Extra and intracranial compensation for steno-occlusions of cerebral vessels. The role of US.

 

 

 

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