Indications
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Despite advances in endovascular neurosurgery, cerebral bypass operations remain essential components in the management of giant aneurysms and some skull base tumors involving the carotid artery. Sacrifice of the internal carotid artery (ICA), either inadvertently or in a planned fashion, can be associated with substantial mortality (5%) and morbidity (15%).
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For the management of intracavernous or proximal carotid aneurysms and carotid-cavernous fistulas and radical resection of cavernous tumors and infratemporal fossa lesions, maintenance of the ICA flow is crucial.
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For cavernous sinus lesions, C6 petrous carotid to paraophthalmic C2 segment interposition saphenous vein graft or external carotid to submandibular subzygomatic pterygoid subtemporal saphenous vein bypass to the M2 inferior branch anastomosis is indicated. For an infratemporal vascular or neoplastic lesion, submandibular external carotid to subtemporal petrous carotid saphenous bypass can be performed, eliminating the infratemporal process or pathology.
Planning and positioning
Types of High-Flow Carotid Bypass
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Type 1 bypass is indicated for the management of intracavernous giant aneurysms and cavernous carotid stenosis and for radical resection of invasive meningioma or malignant tumors in this location.
Figure 33-2:
Fukushima bypass type 2. External carotid to petrous C6 infratemporal saphenous graft.
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Type 2 bypass is indicated for the repair of infratemporal or high cervical aneurysms, dissecting aneurysms, and stenosis and radical resection of infratemporal meningiomas or glomus tumors.
Figure 33-3:
Fukushima bypass type 3. External carotid to M2 saphenous vein graft.
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Type 3 bypass is used for management of proximal carotid aneurysms and intracavernous aneurysms.
Figure 33-4:
Fukushima bypass type 4. External carotid to P2 segment saphenous graft.
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Type 4 bypass is used for the management of basilar artery giant aneurysms.
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Preoperative evaluation includes a complete neurologic examination and assessments for visual function, respiratory status, cardiovascular status, diabetes mellitus, and gastrointestinal function. Preoperative routine laboratory values (complete blood count, coagulation profile, electrolytes, chemistry, and basic metabolic profile), chest x-ray, and electrocardiogram are essential.
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In addition to the standard neurologic examinations of computed tomography (CT), magnetic resonance imaging (MRI), or magnetic resonance angiography, a four-vessel catheter angiogram is essential for neuroradiologic evaluation of the vascular process. Frequently, a balloon occlusion test is indicated for assessment of cross flow or collateral circulation capacity.
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The patient is given a dose of preoperative antibiotics and dexamethasone (10 to 20 mg intravenously) before the skin incision. Brain relaxation is achieved with mannitol (25 to 50 g intravenously), furosemide (Lasix; 20 to 40 mg intravenously), and hyperventilation. When a tight brain is expected, a lumbar catheter may be inserted for continuous cerebrospinal fluid drainage intraoperatively and postoperatively. For temporary arterial occlusion during a difficult anastomosis procedure, a moderate dose of intravenous heparin (2000 to 4000 U), moderate hypothermia (33° C to 35° C), and barbiturate burst suppression pharmacologic brain protection may be used.
Positioning
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Generally, the patient’s upper torso is elevated 15 degrees, and the operating table is positioned at 15 degrees reverse Trendelenburg position to maintain the head above the level of the heart.
Procedure
Skin Incision
Skin Flap Reflection
