Transcranial Doppler ultrasound criteria for hemodynamically significant internal carotid artery stenosis based on residual lumen diameter calculated from en bloc endarterectomy specimens

Background and Purpose Transcranial Doppler (TCD) is often used in conjunction with carotid duplex ultrasonography (CDUS) to evaluate the hemodynamic significance of internal carotid artery (ICA) stenosis. We examined the sensitivity and specificity of TCD criteria for detection of a hemodynamically significant stenosis (residual lumen diameter <1.5 mm) at the origin of the ICA. Methods We selected patients who underwent carotid endarterectomy (CEA) and had preoperative TCD data available. Eighty-one patients underwent transorbital evaluation, 49 of whom also had transtemporal TCD performed. The endarterectomy specimens were removed en bloc and sectioned, and the minimal residual lumen diameter calculated by computer analysis. Results For the transorbital approach, the strongest indicators of a residual lumen diameter <1.5 mm were reversed flow in the ipsilateral ophthalmic artery and a >50% peak systolic velocity difference between the carotid siphons (distal ICAs) in patients with unilateral ICA origin stenosis. They were 100% specific and 31% and 26% sensitive, respectively. For the transtemporal approach in patients with a unilateral stenosis, a >35% difference in ipsilateral middle cerebral artery (MCA) peak systolic velocity relative to the contralateral MCA or a >50% difference in contralateral anterior cerebral artery (ACA) peak systolic velocity relative to the ipsilateral ACA were 100% specific for identifying a residual lumen diameter of <1.5 mm. Sensitivities were 32% and 43%, respectively. Irrespective of contralateral stenosis, a >35% difference in ipsilateral MCA peak systolic velocity relative to the ipsilateral posterior cerebral artery had a 100% specificity and a 23% sensitivity for detecting a <1.5 mm minimal residual lumen diameter. Conclusions Although the TCD sensitivity for detecting a hemodynamically significant stenosis is relatively low, it can be highly specific (up to 100%). We conclude that TCD enhances the specificity of highly sensitive CDUS criteria for detecting a hemodynamically significant ICE stenosis.