It is essential to accurately assess the degree of carotid artery stenosis in deciding whether to perform revascularization. Although there has been much confusion because two clinical trials—i.e., NASCET (North American Symptomatic Carotid Endarterectomy Trial) [5] and ECST (European Carotid Surgery Trial) [6]—have been conducted to evaluate carotid endarterectomy (CEA) using different methods to assess the degree of stenosis, the NASCET method is currently the most widely utilized (Fig. 30.2a, b). The NASCET method more accurately reflects hemodynamic features, whereas the ECST method more accurately reflects plaque burden around the stenosis. However, the accuracy of the ECST method is lower because measurements are obtained by drawing an imaginary line over the carotid bulb, and thus it is highly likely for different testers to obtain different measurement results. For this reason, the ECST method may produce exaggerated assessment results with regard to stenosis when compared with the NASCET method [7, 8]. Based on the NASCET measurement method, carotid artery stenosis can largely be classified into no stenosis, mild stenosis (<50% stenosis), moderate stenosis (50–69% stenosis), severe stenosis (>70% stenosis), and occlusion, and the treatment approach can be determined according to the degree of stenosis [7, 8].

In patients who have experienced an ischemic stroke due to significant carotid artery stenosis, CEA or carotid artery stenting (CAS) should be considered. Because there are two methods that can be used in such patients, the physician should select the most optimal method for each patient by analyzing previous clinical trial results objectively and in detail and by applying the results appropriately to the treatment center where the physician is working. Below, we analyze and summarize important clinical trial findings regarding CEA and CAS and make recommendations for treatment based upon these findings.