Rescue collateral flow in color duplex sonography

Occlusion of the common carotid artery (CCA) is generally associated with the absence of blood flow beyond the occluded CCA. However, collateral circulation may preserve the patency of the vessel distal to the occluded CCA, and the occipital artery may provide a rescue connection between the carotid and vertebral arteries when either one is occluded. The accuracy of color duplex sonography in identifying the CCA occlusion (CCAO) is 97% with a sensitivity of 91% and a specificity of 99%. It is also very useful in defining the patent distal vessels above an occluded CCA. In this study, we report a case of a CCAO that showed a patent internal carotid artery (ICA) and external carotid artery (ECA). We describe the color duplex sonographic appearance of the collateral circulation.