The University of Iowa

Carotid Occlusion Surgical Study (COSS)


The Carotid Occlusion Surgery Study (COSS) was conducted to determine if superficial temporal artery-middle cerebral artery (STA-MCA) bypass, when added to the best medical therapy, would reduce subsequent ipsilateral stroke in patients with complete internal carotid artery (ICA) occlusion and an elevated oxygen extraction fraction (OEF) in the cerebral hemisphere distal to the occlusion. Despite excellent bypass graft patency and improved cerebral hemodynamics, STA-MCA anastomosis did not provide an overall benefit regarding ipsilateral 2-year stroke recurrence, mainly because of  much better than expected stroke recurrence rate in the medical group, but also because of a significant postoperative stroke rate. 

Trial results can be viewed on