Note the presence of color flow signal through a fistula (arrow) between the external carotid artery and the internal jugular vein, causing turbulence in the latter.1 indicates internal jugular vein; 2, common carotid artery; 3, internal carotid artery; and 4, external carotid artery.olor Doppler investigation demonstrated blood flow from the external carotid artery into the internal jugular vein, causing turbulence in the latter during systole (Figure 1) but not during diastole (Figure 2).