If the collateral circulation is adequately compensated it may be asymptomatic, while inadequate compensation may cause transient or permanent hemiparesis, hemianopia, hemianesthesia, and inability to speak. Other less common symptoms include limb tremors, unilateral visual impairment, and syncope.
Non-specific clinical manifestations include headache and cognitive impairment; headaches due to chronic internal carotid artery occlusion are often poorly described chronic headaches that may be associated with the establishment of collateral circulation following chronic occlusion of the carotid artery and abnormal pulsation of the external carotid artery, and vascular dementia may be associated with chronic cerebral ischaemia due to chronic internal carotid artery occlusion.