Four collateral circulation pathways were observed after common carotid artery occlusion

Common carotid artery (CCA) occlusion (CCAO) is a rare condition. Owing to collateral circulation, ipsilateral internal carotid artery (ICA) and external carotid artery (ECA) are often patent. This study included 16 patients with unilateral CCAO and patent ipsilateral ICA and ECA. The pathways which supplied ICA were investigated by digital subtraction angiography (DSA), transcranial Doppler (TCD), magnetic resonance angiography (MRA) and computed tomography angiography (CTA). In all 16 patients, TCD found antegrade blood flow in ipsilateral ICA, which was supplied by retrograde blood flow in ipsilateral ECA through carotid bifurcation. We call this phenomenon "ICA steal". DSA and CTA discovered four pathways of ICA steal, including 1) ipsilateral vertebral artery - occipital artery - ECA - ICA, 2) ipsilateral thyrocervical trunk or costocervical trunk - ascending cervical artery or deep cervical artery - occipital artery - ECA - ICA, 3) contralateral ECA - contralateral superior thyroid artery - ipsilateral superior thyroid artery - ipsilateral ECA - ICA, and 4) ipsilateral thyrocervical trunk - inferior thyroid artery - superior thyroid artery - ECA - ICA. ICA is possible to be patent and supplied by several collateral circulation pathways after CCAO.