Contralateral internal carotid artery stenosis or occlusion: pitfall of correct ipsilateral classification--a study performed with color-flow imaging.

The records of 183 patients who had undergone color-flow imaging of the extracranial carotid arteries and subsequent bilateral cerebral arteriography were reviewed to determine whether contralateral carotid arterial disease adversely affects the accuracy of duplex scanning by increasing the velocity of flow in the ipsilateral artery. In 83 arteries the contralateral internal carotid artery had a diameter reduction greater than or equal to 80%; in the remaining 283, the contralateral artery was less severely diseased. Noninvasive findings correlated less well with arteriography in the group with contralateral disease (k = 0.69 +/- 0.06) than in the group with less severe contralateral stenosis (k = 0.78 +/- 0.03), and the incidence of false-positive errors was significantly (p = 0.02) higher (18% vs 7%). For all categories of ipsilateral stenosis, the mean peak systolic and end-diastolic velocities were elevated in the group with severe contralateral disease. This effect was most evident in the 50% to 79% diameter reduction category, especially in reference to the end-diastolic velocity (p = 0.2). However, the data correlating velocity with diameter reduction were widely scattered, indicating that the effect of contralateral disease is inconsistent. We conclude that severe disease of the contralateral carotid artery can lead to overreading ipsilateral disease and that velocity determinations should be interpreted cautiously under such circumstances.