The Carotid and Middle Cerebral Artery Occlusion Surgery Study

Overview

The recently published Carotid Occlusion Surgery Study (COSS) failed to show a benefit of extracranial-intracranial (EC-IC) bypass surgery over medical therapy in patients with symptomatic hemodynamically significant carotid occlusion. Since then on, different controversies have been raised on several aspects including the study population, qualifications of surgeons and hemodynamic evaluation. In COSS protocol, the primary inclusion population is the patient demonstrating occlusion of unilateral ICA while the contralateral ICA less than 50% stenosis. Because of the enrollment problems, in the final result report, 18% patients suffered from contralateral ICA stenosis more than 50%. As we known, COSS utilized oxygen extraction fraction (OEF) ratio by PET as the criterion of hemodynamic evaluation. Bilateral ICAs lesion will disturbed the ratio even the identifying the subgroup of patients with hemodynamic insufficiency. As an interventional trial, the COSS should ensure the certification for the experienced surgeons. While for expanding the number of centers and enhancing recruitment, COSS made some concessions on the surgeons training and certification. The 15% postoperative event rate is not the best that can be achieved according to recent surgical technical development. The cerebral hemodynamic insufficiency has been considered as the primary pathophysiological factor for patients with ICA or MCA occlusion. For these patients, antiplatelet therapy is not likely to prevent hemodynamic stroke.EC-IC bypass surgery probably will be the possible effective therapy. These underlying assumptions deserved further exploration and more strict research.So the CMOSS study in China is designed to compare the efficacy and safety of EC-IC bypass surgery with medical therapy in patients with symptomatic hemodynamically significant carotid occlusion.

Patients with symptoms of cerebral or retinal ischemia associated with ipsilateral internal carotid artery (ICA) occlusion have an annual risk of 5-8% of recurrent ischemic stroke. While in China, the incidence of middle cerebral artery (MCA) occlusion is higher than in western countries. The annual risk of recurrent ischemic stroke in patients with symptomatic ICA or MCA occlusion has not improved over the years. The proportion of recurrence that was minor disabling was rather high.