Bypass grafts are employed to circumvent restrictions to cerebral blood flow. The more commonly employed conduits include saphenous veins, superficial temporal arteries, and occipital arteries. Bypass procedures may route blood from the extracranial circulation (carotid or vertebral) to the intracranial circulation [extracranial-intracranial (EC-IC) bypass] or directly reconstruct the intracranial circulation (intracranial bypass). Using these procedures, neurosurgeons successfully treat complex vascular lesions that would otherwise result in ischemic morbidity.
Cerebral bypass procedures have been incorporated in the management of patients with difficult aneur-ysms, neoplastic disease, and traumatic arterial dissection and in patients with ischemic disease refractory to medical therapy. Vascular neurosurgeons employ bypass techniques to redirect flow around giant aneurysms that cannot be directly clipped and require parent vessel occlusion. Cerebral bypass has also been employed in the successful management of symptomatic traumatic internal carotid artery dissection. Skull base surgeons use bypass techniques when faced with tumors encasing large cerebral arteries whose removal requires vessel sacrifice. Despite the negative results of the Cooperative Study of Extracranial-Intracranial Arterial Anastomosis, with appropriate preoperative selection, patients with focal intracranial vascular disease may still benefit from EC-IC bypass. This is particularly true for those patients who have
been screened with ancillary tests, such as xenon CT with and without acetozolamide challenge, documenting inadequate cerebrovascular reserve and collateral flow.
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