Your brain receives blood through the right and left carotid arteries, which run through your neck and enter the skull to provide oxygen and nutrients. These arteries can become narrowed or occluded, reducing blood supply to the brain, and lead to stroke (death of brain tissue, producing weakness, speech impairment and paralysis).
Extra cranial to intracranial (EC-IC) bypass surgery is performed to increase blood supply to the brain by surgically connecting the external carotid artery in your neck with the internal carotid artery inside your skull, thereby bypassing the area of blockage. This may be done by directly connecting the branches of the internal and external carotid arteries or using a vein graft taken from your leg.
EC-IC is indicated for the following reasons: