Extracranial-intracranial bypass for ischemic cerebrovascular disease: what have we learned from the Carotid Occlusion Surgery Study?

Abstract

<jats:p>Extracranial-intracranial (EC-IC) arterial bypass has been used in the treatment of various neurosurgical pathologies including skull base tumors requiring sacrifice of a large intracranial artery; complex intracranial aneurysms requiring trapping; and distal revascularization, moyamoya disease, and symptomatic cerebrovascular stenoocclusive disease. The latter indication has been the subject of intense investigations in several large randomized controlled trials, most recently the Carotid Occlusion Surgery Study (COSS). In the present literature review and synthesis, the authors examine the current evidence available for EC-IC arterial bypass for the treatment of ischemic cerebrovascular disease including both extracranial carotid artery occlusive disease and intracranial atherosclerotic disease. They focus particular attention on EC-IC arterial bypass for the treatment of symptomatic hemodynamic cerebral ischemia and how lessons learned from the COSS might guide future investigations into the treatment of this disease.</jats:p>

Role of and Indications for Bypass Surgery After Carotid Occlusion Surgery Study (COSS)?

“…The St Louis Carotid Occlusion Study (STLCOS) 33 was a prospective study showing that symptomatic patients with carotid occlusion and presenting stage II hemodynamic impairment (increased oxygen-extractionfraction with positron emission tomography [OEF-PET]) were at significantly increased risk of ipsilateral stroke at 2 years compared with patients without stage II hemodynamic impairment (26.5% versus 5.3%). 28,33 During the same period, several other studies demonstrated that in stage II patients bypass was able to improve or even normalize the hemispheric OEF ratios postoperatively. 28 Therefore, all the conditions were present to justify a new RCT to test the hypothesis that EC-IC bypass surgery would benefit patients with recently symptomatic atherosclerotic carotid occlusion when selected according to strict validated hemodynamic criteria.…”

“…No significant difference in the incidence of fatal and nonfatal ischemic strokes was reported. 4,28 This study was fiercely debated. 32 One of the primary criticisms related to the lack of hemodynamic criteria used to identify and select those high-risk patients who might benefit most from bypass 28,33,34 A Cochrane review 31 published in 2010 reported the results of 21 trials (2 RCTs and 19 nonrandom studies) for total of 2591 patients with symptomatic carotid occlusion.…”

“…4,5 Indirect cerebral revascularization methods are felt to be largely ineffective for non-moyamoya vasculopathy 28,29 because of the presumed absence of the angiogenic milieu associated with MMD, although small case series have suggested some limited success with indirect strategies. 30 Currently, a RCT, the EDAS (Surgical) Revascularization in patients with Symptomatic Intracranial Arterial Stenosis (ERSIAS) is underway in the United States, which may provide some insights into the role of indirect bypass for atherosclerotic disease (ClinicalTrials.gov NCT01819597; EDAS: encephalo-duro-arterio-synangiosis).…”

“…Beyond this, for atherosclerotic occlusions, the primary focus has been on examining the role of direct cerebral bypass. 28,31 The EC-IC bypass trial published in 1985 was the first prospective RCT aimed at investigating whether EC-IC bypass was superior to best medical therapy alone for stroke prevention. 4 The study was conducted in 1377 symptomatic patients with (1) 1 or more TIAs or minor ischemic strokes within 3 months of enrollment, and 1 of the following: (2) stenosis or occlusion of the MCA proximal trunk, (3) stenosis of the ICA above the C-2 vertebral body (inaccessible to carotid endarterectomy), or (4) atherosclerotic ICA occlusion.…”

“…31 Again most of the analyzed studies lacked hemodynamic criteria for patients' inclusion. 28 After the EC-IC bypass trial, methods and criteria for quantification and assessment of cerebral hemodynamic impairment were validated (Figure 3). The St Louis Carotid Occlusion Study (STLCOS) 33 was a prospective study showing that symptomatic patients with carotid occlusion and presenting stage II hemodynamic impairment (increased oxygen-extractionfraction with positron emission tomography [OEF-PET]) were at significantly increased risk of ipsilateral stroke at 2 years compared with patients without stage II hemodynamic impairment (26.5% versus 5.3%).…”