Patent internal and external carotid arteries beyond an occluded common carotid artery: report of a case diagnosed by color Doppler.

Occlusion of the common carotid artery (CCA) is most often associated with thrombosis of the distal vessels. In rare cases, however, a weak antegrade flow can still be detected in the internal carotid artery (ICA). This patency is the result of a retrograde perfusion of the ipsilateral external carotid artery (ECA) via its collaterals. Such situation should not be ignored since bypass surgery can easily allow for effective restoration of flow. Most authors agree to say that color flow duplex imaging (CFDI) has now become the hallmark to detect a patent ICA in spite of a CCA occlusion.