Reversed flow in the external carotid artery despite a patent but stenosed common carotid artery.

BACKGROUND AND PURPOSE Occlusion of the common carotid artery (CCA) is generally associated with an occlusion of the ipsilateral internal carotid artery (ICA) or of the external carotid artery (ECA) or of both. Sometimes, collateral circulation to the ECA may preserve patency of the ICA via retrograde perfusion through the bulb. We herewith report a case of reversed flow in the ECA in the presence of a patent but stenosed CCA as diagnosed with color-coded duplex flow imaging (CDFI). CASE REPORT This 85-year-old right-handed man was admitted for rapidly regressive acute dysarthria associated with left hemiparesis. Diffusion-weighted magnetic resonance (MR) imaging showed an acute ischemic lesion in the territory of the right middle cerebral artery. MR angiography showed patency of the right ICA and ECA but an occlusion of the CCA was suspected. CDFI demonstrated patency of the right CCA with a high-resistance pattern due to a large, partially calcified, stenosing atheromatous plaque. Surprisingly, reversed flow was observed in the right ECA of which signal was dampened. CONCLUSION Collateralization with reversed flow in the ECA may occur in a patent but stenosed CCA associated with a high-grade stenosis of the carotid bifurcation. CDFI is a very useful tool to detect such hemodynamic conditions.