The Role of Extracranial–Intracranial Bypass in Current Practice Mark A. Adelman and Mikel Sadek Multiple indications exist for constructing an extracranial–intracranial (EC-IC) bypass. The indications that are encountered most frequently in contemporary practice are symptomatic occlusion of the internal carotid artery (ICA), stenosis or occlusion of the intracranial vasculature, usually at the level of the carotid siphon or middle cerebral artery (MCA), and intracranial aneurysms that are not amenable to endovascular treatment or to open ligation. Patients with an ipsilateral ICA occlusion have an annual stroke risk of 5% to 7% as well as an annual risk of ipsilateral stroke of 2% to 6%. Moreover, 15% of patients with anterior circulation ischemia are found to have ipsilateral occlusion of the ICA. Cerebral ischemia can occur secondary to thromboembolism from the distal occluded stump or to diminished cerebral blood flow. Anticoagulation or antiplatelet therapy is considered ineffective in the treatment of ICA occlusion, and performing an ipsilateral EC-IC bypass can prevent recurrent cerebral ischemic events in a subset of symptomatic patients. In patients who elect conservative management initially, an EC-IC bypass may be constructed if symptoms develop or progress despite maximal medical therapy. Other indications that require the consideration for an EC-IC bypass include ischemic ocular syndromes, moyamoya disease, vertebrobasilar insufficiency, oncologic resections, and chronic low-perfusion syndromes. Historical Perspective The first EC-IC bypass was reported by Donaghy and colleagues in 1967, and the procedure was in widespread use during the following decade. The most commonly performed variation was the superficial temporal artery–to–MCA bypass. Initial nonrandomized retrospective and prospective studies supported the safety and efficacy of the procedure. In addition to studies demonstrating an improvement in cerebral hemodynamics following EC-IC bypass based on functional imaging, improved clinical outcomes were demonstrated as well, especially in patients with poor collateral circulation. One study demonstrated that in 49 patients who presented with an ICA occlusion, treatment that included performing an EC-IC bypass was particularly effective for patients who were symptomatic or who had significant contralateral carotid artery stenosis. Two randomized trials have been performed since the inception of the procedure. The first and larger was the EC-IC Bypass Study Group trial that was conducted in the mid-1980s. The EC-IC Bypass Study Group trial was designed as an international multicenter prospective randomized trial that evaluated the use of EC-IC bypass for treating symptomatic cerebrovascular stenosis or occlusion. Patients were evaluated who presented with one or more transient ischemic attacks (TIAs), or strokes with associated stenosis, or occlusion in the affected ICA or MCA distributions. Cerebrovascular lesions were stratified according to the following anatomic landmarks: ICA occlusion, stenosis of the ICA above the second cervical vertebrae (C2), and MCA stenosis or occlusion. A total of 1377 patients were randomized to either EC-IC bypass (n = 714) or best medical management (n = 663). Best medical management at the time consisted of acetylsalicylic acid (325 mg up to four times per day) with appropriate control of hypertension. The mean follow-up interval was 56 months. In the surgical group, postprocedural angiographic patency was achieved in 96% of patients. Within the surgical group, the postoperative mortality and stroke rates were 0.6% and 2.5%, respectively. There was a nonsignificant trend toward increased nonfatal and fatal strokes in the surgical group as compared with the medically treated group. Subset analyses suggested that patients with severe MCA stenosis or occlusion of the ICA fared worse. Regardless, statistical significance was not achieved for any of the primary outcomes within the study. The study concluded that EC-IC bypass failed to demonstrate benefit in preventing ischemic events postoperatively as compared with medical management. The most recently completed randomized trial was the Japanese EC-IC bypass trial (JET). The trial studied 195 patients who were symptomatic and who exhibited cerebrovascular hemodynamic compromise as measured by functional imaging; these patients were randomized to EC-IC bypass or to best medical care. The average follow-up was 25 months, and mortality rates were low for both groups (surgery, n = 2; medical, n = 1). Moreover, there were no significant differences between the surgical and medical treatment groups in all other adverse events measured. The trial concluded that there were no significant differences in outcomes between the surgical and medical groups. Multiple criticisms were raised against both trials. The EC-IC Bypass Study Group was criticized for having inadequate randomization with regard to baseline criteria. Only stable low-risk patients were included in the study, which did not necessarily reflect the group that was being treated in the general population. In addition, there was no stratification for cerebrovascular hemodynamic compromise. More specifically, patients with embolic strokes but adequate collateral flow from the contralateral circulation as evidenced by functional imaging were not differentiated from stroke patients with compromised cerebrovascular hemodynamics. Despite these criticisms, EC-IC bypass procedure volume diminished significantly in subsequent years. The Carotid Occlusion Surgery Study (COSS) is a randomized control trial that is under way to reassess outcomes for EC-IC bypass. The study is designed to evaluate patients specifically with cerebrovascular hemodynamic compromise ipsilateral to a symptomatic carotid occlusion as measured by oxygen extraction fraction using positron emission tomography (PET). The hypothesis is that patients with impaired hemodynamics, whose strokes result from a low-flow state, might benefit preferentially from an EC-IC bypass. Procedural Characteristics Preoperative Evaluation The goal of the preoperative evaluation is to diagnose and characterize the pathology being treated as well as to differentiate who will tolerate vascular occlusion as a sole therapeutic option and who will require the construction of an EC-IC bypass. In general, contrast imaging is required preoperatively to delineate the anatomy. This may be performed using computed tomography angiography (CTA), magnetic resonance angiography (MRA), or digital subtraction angiography (DSA). In addition, a brain-perfusion scan or balloon occlusion test may be obtained to assess for adequacy of direct and collateral cerebral blood flow. The balloon occlusion test might produce no change in blood flow, a mild decrease in global blood flow, or a marked asymmetric decrease in blood flow, suggesting significant cerebrovascular hemodynamic compromise. Procedural Considerations The creation of an EC-IC bypass follows the same tenets as the creation of vascular bypasses elsewhere in the periphery: inflow, outflow, and conduit. The inflow can vary depending on the clinical situation. Possible inflow vessels include the common carotid artery (CCA), the internal carotid artery (ICA), the external carotid artery (ECA), or a branch off of the ECA. If given the option, the surgeon should select the inflow vessel in the following order or preference: ECA preferred to CCA preferred to ICA. The preferential use of the ECA or CCA as the inflow vessel diminishes the risk of cerebral ischemia secondary to a low-flow state during clamping of the proximal anastomosis. Two commonly used outflow vessels include the ICA or MCA. The latter is accessed through a pretragal (zygoma) tunnel. Other options exist for the outflow vessel, and the choice depends on the location of the pathology being treated. With regard to the conduit, the common options include the saphenous vein or the radial artery. The radial artery graft is used preferentially at our institution owing to a better size match resulting in a theoretical improvement in flow dynamics. In addition, the use of distal vein requires valvular lysis, because it needs to be used in a nonreversed fashion to minimize size discrepancy. Successful harvesting of the radial artery depends on appropriate preoperative planning and selection. In general, the nondominant arm should be used. Pulse volume recordings and compression studies should be performed to assess adequacy of collateral flow to the hand. Most significantly, digital pulse volume recordings or angiography should be used to confirm the presence of a patent palmar arch. Following appropriate preoperative planning, the procedure is conducted in three stages. The first stage consists of performing the usual exposure and isolation of the CCA, ICA, and ECA using an incision along the anterior sternocleidomastoid. The target intracerebral vessel is exposed and isolated using a pterional craniotomy. The final component of the exposure consists of isolating the radial artery. This is carried out in a standard fashion with care to preserve the radial nerve. The harvested artery is flushed using a combination of heparin (1000 U), papaverine (20 mg), and nitroglycerine (1 mg) in 1 L of a crystalloid solution. At this point, a pretragal soft-tissue tunnel with a furrow at the base of the zygoma is created, and an arteriovenous graft tunneler is used to tunnel the conduit. The second stage of the procedure consists of performing the distal anastomosis. This is performed before the proximal anastomosis to allow additional maneuverability of the graft. The patient is heparinized (100 U/kg), and dexamethasone and barbiturates are administered until cerebral activity is suppressed adequately as monitored by electroencephalogram (EEG). A 5-mm arteriotomy is made in the target vessel, and an end-to-side anastomosis is constructed using interrupted 8–0 or 9–0 Prolene sutures. The conduit is drained and air is removed, after which the conduit is clamped and the intracerebral vessel is reperfused. The third stage of the procedure consists of performing the proximal anastomosis. At this point an end-to-side anastomosis is performed at the desired site, usually using a 6–0 Prolene suture. Before the ICA is ligated, the ICA is accessed using a 20-gauge angiocatheter. The native artery is clamped, and the bypass patency is assessed using DSA. Evoked potentials are used to assess for hypoperfusion before the ICA is ligated. Once adequacy of flow is confirmed, the ICA is suture ligated at its origin or immediately distal to the proximal anastomosis. Protamine is used at the end of the procedure for reversal of anticoagulation. Aspirin is initiated postoperatively and continued indefinitely. Only gold members can continue reading. 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The Role of Extracranial–Intracranial Bypass in Current Practice Mark A. Adelman and Mikel Sadek Multiple indications exist for constructing an extracranial–intracranial (EC-IC) bypass. The indications that are encountered most frequently in contemporary practice are symptomatic occlusion of the internal carotid artery (ICA), stenosis or occlusion of the intracranial vasculature, usually at the level of the carotid siphon or middle cerebral artery (MCA), and intracranial aneurysms that are not amenable to endovascular treatment or to open ligation. Patients with an ipsilateral ICA occlusion have an annual stroke risk of 5% to 7% as well as an annual risk of ipsilateral stroke of 2% to 6%. Moreover, 15% of patients with anterior circulation ischemia are found to have ipsilateral occlusion of the ICA. Cerebral ischemia can occur secondary to thromboembolism from the distal occluded stump or to diminished cerebral blood flow. Anticoagulation or antiplatelet therapy is considered ineffective in the treatment of ICA occlusion, and performing an ipsilateral EC-IC bypass can prevent recurrent cerebral ischemic events in a subset of symptomatic patients. In patients who elect conservative management initially, an EC-IC bypass may be constructed if symptoms develop or progress despite maximal medical therapy. Other indications that require the consideration for an EC-IC bypass include ischemic ocular syndromes, moyamoya disease, vertebrobasilar insufficiency, oncologic resections, and chronic low-perfusion syndromes. Historical Perspective The first EC-IC bypass was reported by Donaghy and colleagues in 1967, and the procedure was in widespread use during the following decade. The most commonly performed variation was the superficial temporal artery–to–MCA bypass. Initial nonrandomized retrospective and prospective studies supported the safety and efficacy of the procedure. In addition to studies demonstrating an improvement in cerebral hemodynamics following EC-IC bypass based on functional imaging, improved clinical outcomes were demonstrated as well, especially in patients with poor collateral circulation. One study demonstrated that in 49 patients who presented with an ICA occlusion, treatment that included performing an EC-IC bypass was particularly effective for patients who were symptomatic or who had significant contralateral carotid artery stenosis. Two randomized trials have been performed since the inception of the procedure. The first and larger was the EC-IC Bypass Study Group trial that was conducted in the mid-1980s. The EC-IC Bypass Study Group trial was designed as an international multicenter prospective randomized trial that evaluated the use of EC-IC bypass for treating symptomatic cerebrovascular stenosis or occlusion. Patients were evaluated who presented with one or more transient ischemic attacks (TIAs), or strokes with associated stenosis, or occlusion in the affected ICA or MCA distributions. Cerebrovascular lesions were stratified according to the following anatomic landmarks: ICA occlusion, stenosis of the ICA above the second cervical vertebrae (C2), and MCA stenosis or occlusion. A total of 1377 patients were randomized to either EC-IC bypass (n = 714) or best medical management (n = 663). Best medical management at the time consisted of acetylsalicylic acid (325 mg up to four times per day) with appropriate control of hypertension. The mean follow-up interval was 56 months. In the surgical group, postprocedural angiographic patency was achieved in 96% of patients. Within the surgical group, the postoperative mortality and stroke rates were 0.6% and 2.5%, respectively. There was a nonsignificant trend toward increased nonfatal and fatal strokes in the surgical group as compared with the medically treated group. Subset analyses suggested that patients with severe MCA stenosis or occlusion of the ICA fared worse. Regardless, statistical significance was not achieved for any of the primary outcomes within the study. The study concluded that EC-IC bypass failed to demonstrate benefit in preventing ischemic events postoperatively as compared with medical management. The most recently completed randomized trial was the Japanese EC-IC bypass trial (JET). The trial studied 195 patients who were symptomatic and who exhibited cerebrovascular hemodynamic compromise as measured by functional imaging; these patients were randomized to EC-IC bypass or to best medical care. The average follow-up was 25 months, and mortality rates were low for both groups (surgery, n = 2; medical, n = 1). Moreover, there were no significant differences between the surgical and medical treatment groups in all other adverse events measured. The trial concluded that there were no significant differences in outcomes between the surgical and medical groups. Multiple criticisms were raised against both trials. The EC-IC Bypass Study Group was criticized for having inadequate randomization with regard to baseline criteria. Only stable low-risk patients were included in the study, which did not necessarily reflect the group that was being treated in the general population. In addition, there was no stratification for cerebrovascular hemodynamic compromise. More specifically, patients with embolic strokes but adequate collateral flow from the contralateral circulation as evidenced by functional imaging were not differentiated from stroke patients with compromised cerebrovascular hemodynamics. Despite these criticisms, EC-IC bypass procedure volume diminished significantly in subsequent years. The Carotid Occlusion Surgery Study (COSS) is a randomized control trial that is under way to reassess outcomes for EC-IC bypass. The study is designed to evaluate patients specifically with cerebrovascular hemodynamic compromise ipsilateral to a symptomatic carotid occlusion as measured by oxygen extraction fraction using positron emission tomography (PET). The hypothesis is that patients with impaired hemodynamics, whose strokes result from a low-flow state, might benefit preferentially from an EC-IC bypass. Procedural Characteristics Preoperative Evaluation The goal of the preoperative evaluation is to diagnose and characterize the pathology being treated as well as to differentiate who will tolerate vascular occlusion as a sole therapeutic option and who will require the construction of an EC-IC bypass. In general, contrast imaging is required preoperatively to delineate the anatomy. This may be performed using computed tomography angiography (CTA), magnetic resonance angiography (MRA), or digital subtraction angiography (DSA). In addition, a brain-perfusion scan or balloon occlusion test may be obtained to assess for adequacy of direct and collateral cerebral blood flow. The balloon occlusion test might produce no change in blood flow, a mild decrease in global blood flow, or a marked asymmetric decrease in blood flow, suggesting significant cerebrovascular hemodynamic compromise. Procedural Considerations The creation of an EC-IC bypass follows the same tenets as the creation of vascular bypasses elsewhere in the periphery: inflow, outflow, and conduit. The inflow can vary depending on the clinical situation. Possible inflow vessels include the common carotid artery (CCA), the internal carotid artery (ICA), the external carotid artery (ECA), or a branch off of the ECA. If given the option, the surgeon should select the inflow vessel in the following order or preference: ECA preferred to CCA preferred to ICA. The preferential use of the ECA or CCA as the inflow vessel diminishes the risk of cerebral ischemia secondary to a low-flow state during clamping of the proximal anastomosis. Two commonly used outflow vessels include the ICA or MCA. The latter is accessed through a pretragal (zygoma) tunnel. Other options exist for the outflow vessel, and the choice depends on the location of the pathology being treated. With regard to the conduit, the common options include the saphenous vein or the radial artery. The radial artery graft is used preferentially at our institution owing to a better size match resulting in a theoretical improvement in flow dynamics. In addition, the use of distal vein requires valvular lysis, because it needs to be used in a nonreversed fashion to minimize size discrepancy. Successful harvesting of the radial artery depends on appropriate preoperative planning and selection. In general, the nondominant arm should be used. Pulse volume recordings and compression studies should be performed to assess adequacy of collateral flow to the hand. Most significantly, digital pulse volume recordings or angiography should be used to confirm the presence of a patent palmar arch. Following appropriate preoperative planning, the procedure is conducted in three stages. The first stage consists of performing the usual exposure and isolation of the CCA, ICA, and ECA using an incision along the anterior sternocleidomastoid. The target intracerebral vessel is exposed and isolated using a pterional craniotomy. The final component of the exposure consists of isolating the radial artery. This is carried out in a standard fashion with care to preserve the radial nerve. The harvested artery is flushed using a combination of heparin (1000 U), papaverine (20 mg), and nitroglycerine (1 mg) in 1 L of a crystalloid solution. At this point, a pretragal soft-tissue tunnel with a furrow at the base of the zygoma is created, and an arteriovenous graft tunneler is used to tunnel the conduit. The second stage of the procedure consists of performing the distal anastomosis. This is performed before the proximal anastomosis to allow additional maneuverability of the graft. The patient is heparinized (100 U/kg), and dexamethasone and barbiturates are administered until cerebral activity is suppressed adequately as monitored by electroencephalogram (EEG). A 5-mm arteriotomy is made in the target vessel, and an end-to-side anastomosis is constructed using interrupted 8–0 or 9–0 Prolene sutures. The conduit is drained and air is removed, after which the conduit is clamped and the intracerebral vessel is reperfused. The third stage of the procedure consists of performing the proximal anastomosis. At this point an end-to-side anastomosis is performed at the desired site, usually using a 6–0 Prolene suture. Before the ICA is ligated, the ICA is accessed using a 20-gauge angiocatheter. The native artery is clamped, and the bypass patency is assessed using DSA. Evoked potentials are used to assess for hypoperfusion before the ICA is ligated. Once adequacy of flow is confirmed, the ICA is suture ligated at its origin or immediately distal to the proximal anastomosis. Protamine is used at the end of the procedure for reversal of anticoagulation. Aspirin is initiated postoperatively and continued indefinitely. Only gold members can continue reading. 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