The diagnostic value of the resistivity index of the common carotid arteries in severe internal carotid artery stenosis.

Duplex ultrasound is currently used both for screening and for preoperative assessment of the carotid arteries and has completely replaced carotid angiography for the latter purpose in many institutions. The study aimed to identify resistivity index abnormalities in the common carotid arteries in patients with occluded or severely stenosed internal carotid arteries. Sixteen patients with severe internal carotid artery stenosis or occlusion over a twelve-month period were studied by duplex ultrasonography. The resistivity index in the common carotid artery was 0.85 +/- 0.03 on the stenotic side compared to 0.74 +/- 0.04 on the opposite side (p < 0.05). There was no side difference regarding flow velocity. In patients with occluded or severely stenosed internal carotid arteries compensatory vasodilation occurs in cerebral vessels on the same side, and this is also significant, resulting in a decrease in the resistivity index in the common carotid artery of the opposite side.