21 ECA–MCA Bypass with Radial Artery Graft
Abstract
This chapter presents the concept and technique of external carotid artery to middle cerebral artery (ECA–MCA) bypass with radial artery grafts as a rescue strategy for the patients with moyamoya disease (MMD) who failed conventional revascularization.
Failure of direct revascularization with superficial temporal artery (STA) to MCA bypass for MMD is comparatively rare. However, for those cases where a bypass fails to prevent further ischemic attack, safe and efficient rescue strategies are needed.
The indications for rescue revascularization are symptomatic, and the proof of bypass graft failure and impaired cerebrovascular reserve capacity (CVRC) by digital subtraction angiography (DSA) and cerebral blood flow (CBF) study, respectively. As an escape strategy, the radial artery graft bypass from the ECA to M3 or M2 portion is performed.
This strategy may be technically infeasible due to recipient vessel mismatch and high fragility of MMD vessels. Furthermore, there is potential risk for graft occlusion due to thrombosis and hyperperfusion syndrome. To prevent these problems, meticulous surgical manipulation, dilatation of the graft vessel with hydrostatic pressure as a preparation, use of heparin when opening the anastomosis and strict blood pressure control have to be remembered to perform.
The revascularization with radial artery graft provides immediate and reliable augmentation of blood supply. It could be a reasonable option for rescue revascularization, providing satisfying clinical and functional results. However, the number of patients who undergo this technique are so limited because MMD is an uncommon disease and STA–MCA bypass graft failure is rare.
21.1 History and Initial Description
Surgical revascularization for moyamoya disease (MMD) has shown to improve cerebral hemodynamics and prevent further cerebrovascular events. Especially, direct bypass surgery, that is, superficial temporal artery to middle cerebral artery (STA–MCA) bypass, is a potent method to resolve ischemic attacks immediately after surgery. 1
Late failure of STA–MCA bypass is rare, 2 and most of these cases remain asymptomatic and will not result in reoccurrence of ischemic or hemorrhagic symptoms because either accompanying indirect bypass or endogenous collaterals have taken over. 3 However, rarely, late STA–MCA graft failure may cause persistent or new transient ischemic attacks (TIAs) and new ischemic stroke. 4 For these patients, rescue revascularization strategies are needed and most surgeons would elect indirect revascularizations strategies currently. 5 – 7
Large caliber graft bypass using radial artery or saphenous vein grafts for MMD patients has been controversial due to the fear of procedure-related complications, the high fragility of MMD vessels and the potential high risk of hyperperfusion syndrome. 8 , 9 However, the revascularization with large caliber graft provides immediate and reliable augmentation of blood supply. It could be a reasonable option for rescue revascularization, providing satisfying clinical and functional results at a low complication rate. 10
This chapter shows the concept and technique of external carotid artery (ECA) to MCA bypass with radial artery graft as a rescue revascularization for the MMD patients who failed conventional revascularization including STA–MCA bypass.
21.2 Indications
The patient is symptomatic and has new ischemic lesions. The imaging studies demonstrate STA–MCA bypass graft failure on digital subtraction angiography (DSA) and persisting impaired cerebrovascular capacity (CVRC) on cerebral blood flow (CBF) study. Furthermore, no other extradural pedicled graft vessels are available.
21.3 Key Principles
For preparation and harvesting of the radial artery graft, preoperative evaluation of Allen’s test, vessel patency, and length (22–23 cm are needed) are essential. The radial artery graft is passed subcutaneously from the craniotomy incision to the cervical incision. The anastomosis is started with proximal side. When doing the anastomosis of distal side, M3 or distal M2 portion of the MCA is selected as a recipient artery after careful observation to avoid hyperperfusion. The quality of these vessels is usually sufficient for anastomosis. When opening the anastomosis, heparin is used to prevent bypass occlusion. The patency of the graft vessel is confirmed by intraoperative indocyanine green (ICG) angiography and quantitative Doppler flow measurements.
21.4 SWOT Analysis
21.4.1 Strength
Immediate and reliable augmentation of blood supply is gained.
21.4.2 Weaknesses
The procedure may be technically infeasible due to the recipient vessel mismatch and high fragility of MMD vessels.
There is a potential high risk for hyperperfusion syndrome.
21.4.3 Opportunity
The procedure improves current ischemic symptoms and prevents further cerebrovascular events.
21.4.4 Threat
There is the risk for graft occlusion due to vasospasm and thrombosis.
21.5 Contraindications
The contraindications are the primary surgery when STA is available, the proof of fresh ischemic stroke with diffusion weighted imaging, and occlusion of radial artery due to thrombosis.
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