title: Bypass for the prevention of ischemic stroke.
abstract: OBJECTIVE
  Although most ischemic strokes are thromboembolic in origin and their management is endovascular or medical, some are hemodynamic in origin and their management may be surgical. Extracranial-intracranial bypass with superficial temporal artery-to-middle cerebral artery (MCA) bypass, high-flow interposition grafts, and reconstructive techniques have been developed. Clinical indications and efficacy are controversial, and this review examines current practices.
  
  
  METHODS
  Bypass surgery is indicated for patients with athero-occlusive disease that results in chronic, low cerebral blood flow accompanied by episodes of ischemic symptoms. Specific diagnoses include: (1) internal carotid artery occlusion; (2) MCA occlusion and, rarely, high-grade MCA stenosis; (3) vertebrobasilar atherosclerotic steno-occlusive disease; (4) vasculitis resulting in severe occlusive disease; and (5) moyamoya disease.
  
  
  RESULTS
  Discouraging results from the Extracranial-Intracranial Bypass Trial demonstrated the importance of selecting surgical patients based on objective measures of hemodynamic insufficiency. Two such tests are xenon-enhanced computed tomography with acetazolamide challenge and positron emission tomography with measurement of oxygen extraction fraction. Perfusion computed tomography may be another, more practical test. Surgical series, systematic reviews of the literature, and two new randomized clinical trials that use these diagnostic techniques reveal contradictory results. Although they demonstrate that bypass surgery has a morbidity rate of less than 5% and a patency rate of more than 95%, they have not proven a clear benefit.
  
  
  CONCLUSIONS
  Patients with athero-occlusive disease and symptoms of hemodynamic insufficiency have significant risk of stroke if left untreated or managed medically. On the other hand, surgical intervention lacks supporting evidence. Clinicians must individualize their management recommendations until additional data are published or further consensus develops.
authors.affiliation: Department of Neurological Surgery, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Ana
authors.initials: A
authors.lastname: Rodríguez-Hernández
authors.forename: S Andrew
authors.initials: SA
authors.lastname: Josephson
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Josephson
authors.forename: David
authors.initials: D
authors.lastname: Langer
authors.forename: Michael T
authors.initials: MT
authors.lastname: Lawton
mesh_terms: D002545:Brain Ischemia / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control* / Q000601:surgery*; D002548:Cerebral Revascularization / Q000379:methods* / Q000706:statistics & numerical data; D057510:Endovascular Procedures / Q000379:methods*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D020521:Stroke / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control* / Q000601:surgery*