Indications
- If atherosclerosis of the aneurysm neck or the parent artery can make clipping dangerous or impossible;
- If recurrent aneurysms after endovascular coil embolization may be unclippable.
Bypass types
- Type I bypass - Interposition vein grafts
- Type II bypass - Extracranial-to-intracranial bypass with a saphenous vein or radial artery graft
- Type III bypass - Scalp artery (STA or occipital) extracranial-to-intracranial bypass
- Type IV bypass - Direct intracranial revascularization
Principles
- Treatment options include clip occlusion of the aneurysm along with the branching vessel or vessels, parent artery Hunterian ligation, and trapping;
- Not all proximal vessel occlusion often results in ischemia, and proximal vessel occlusion (ICA or vertebral artery) may be tolerated without bypass;
- Occlusion of branches such as the MCA, AICA, and PICA often result in ischemia, and therefore bypass should be considered;
- Preoperative evaluation by angiography and balloon test occlusion (with or without hypotensive provocative testing or cerebral blood flow measurements) may aid in the identification of patients who can tolerate carotid sacrifice;
- Even if the patient passes a balloon test occlusion, there remains up to a 20 % chance of stroke with complete occlusion without a bypass.
Techniques
- Normal blood flow of the MCA is about 250 mL/min;
- Blood flow of saphenous vein graft is 70–140 mL/min;
- Blood flow of radial artery graft is 40 and 70 mL/min;
- Blood flow of STA graft is 15–30 mL/min;
- Blood flow through a saphenous vein graft, which averages about 4–5 mm in diameter, is high enough to support the circulation in an entire major arterial territory at a level well above the ischemic threshold;
- Blood flow of saphenous vein graft typically ranges from 70 to 140 mL/ min and can exceed 250 mL/min;
- The Radial artery graft can be used, which has a smaller diameter than saphenous vein graft (about 3.5 mm);
- In saphenous vein graft, it is important to pass the saphenous vein so that the end that was proximal in the leg is the end used for the cranial, distal anastomosis (because of the unidirectional valve arrangement).
Complications
- The most serious acute complication is early graft occlusion;
- If there is any doubt about the integrity of the graft, intraoperative angiography should be considered;
- Rate of ischemic complications and graft occlusion typically exceeds 10 %;
- A normal flow signal should be confirmed with intraoperative Doppler assessment;
- Subdural or epidural hematomas (or both) developed postoperatively, some of these hematomas were small and asymptomatic.
Author
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Samer S. Hoz, MDNeurosurgeon Consultant |
