Indications
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Atherosclerotic carotid artery occlusion with hemodynamic insufficiency . In nonselected patient populations, a multicenter randomized controlled trial showed no benefit of superficial temporal artery–middle cerebral artery (STA-MCA) bypass for patients with symptomatic carotid occlusive disease. Two more recent natural history studies suggest, however, that a discrete subpopulation of patients with symptomatic carotid occlusion—patients with “misery perfusion,” defined as increased oxygen extraction fraction on positron emission tomography (PET)—are at very high risk for future ischemic events and that this patient population may benefit from surgical revascularization. The Carotid Occlusion Surgery Study was designed to examine the effect of STA-MCA bypass (vs. best medical therapy) on the incidence of recurrent ischemic stroke in patients with symptomatic carotid occlusion and “misery perfusion” on PET. Results from this ongoing clinical trial are likely to provide a definitive answer to this important question.
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Moyamoya disease with ischemic symptoms . Although not validated by a large randomized controlled trial, it is generally accepted that surgical revascularization for patients with moyamoya disease with ischemic symptoms is beneficial. This conclusion is based on multiple case series indicating that STA-MCA bypass provides long-term reduction in ischemic symptoms in adult patients with moyamoya disease. Whether adult patients with moyamoya disease with hemorrhagic symptoms also benefit from STA-MCA bypass is unknown.
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Complex intracranial aneurysms and skull base tumors . Surgical revascularization is frequently performed during complex intracranial procedures to prevent ischemic complications after planned sacrifice of a major intracerebral artery. STA-MCA bypass is often the procedure of choice when the amount of flow augmentation required is modest (e.g., sacrifice of an M2 branch of the MCA, occlusion of the internal carotid artery in a patient with mild hemodynamic compromise by temporary balloon occlusion testing).
Contraindications
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Atherosclerotic carotid artery occlusion without hemodynamic insufficiency . These patients have a documented benign natural history that does not justify surgical revascularization.
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Atherosclerotic intracranial artery stenosis. These patients were at high risk for ischemic complications after STA-MCA bypass in the aforementioned randomized controlled trial.
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Cerebral vasospasm. Emergent STA-MCA bypass for the treatment of cerebral vasospasm has been reported in a few small case series to date; however, its efficacy in these patients remains unproven.
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Planned sacrifice of a major intracerebral artery in patients with marked hemodynamic compromise by temporary balloon occlusion testing. These patients require a high-flow bypass procedure using a radial artery or saphenous venous graft.
Planning and positioning
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All patients should undergo the following: (1) Detailed history and physical examination with particular attention paid to cardiovascular risk factors; (2) computed tomography (CT) or magnetic resonance imaging (MRI) study of the brain (or both); and (3) catheter cerebral angiogram, including select injections of the external carotid arteries to assess adequacy of the STA for bypass. For patients with chronic ischemia, radiographic assessment of cerebrovascular reserve should be considered (e.g., PET, transcranial Doppler ultrasonography, single photon emission computed tomography, xenon CT, perfusion CT). For patients in whom sacrifice of a major intracerebral artery is being contemplated, temporary balloon occlusion testing should be considered to assess adequacy of the collateral circulation and to help determine the extent of revascularization required.
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For patients undergoing STA-MCA bypass for chronic ischemia (e.g., patients with carotid occlusion or moyamoya disease), special anesthetic considerations must be adhered to throughout the procedure. Specifically, normal-to-high mean arterial pressures and normal arterial carbon dioxide levels (38 to 42 mm Hg) must be strictly maintained to avoid ischemic complications related to the vulnerable hypoperfused cerebral hemispheres.
Figure 32-1:
Preoperative catheter angiogram showing select injection of the right internal carotid artery (ICA) in a patient with moyamoya disease. The supraclinoid portion of the ICA cannot be visualized because of stenoocclusion. The anterior (frontal) and posterior (parietal) branches of the STA are easily distinguishable. The middle meningeal artery (MMA) may also be delineated given its location just proximal to the STA.
Figure 32-2:
The patient is administered general endotracheal anesthesia with a combination of inhaled and intravenous agents. The patient is placed in the supine position with the head immobilized in three-point fixation pins and a bump underneath the ipsilateral shoulder. The presumed site of arterial anastomosis should be positioned at the apex to avoid pooling of cerebrospinal fluid in the operative field. The head is elevated 10 to 15 degrees to promote venous drainage.
Procedure
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