Satoshi Hori and Peter Vajkoczy
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.
Keywords: moyamoya disease, STA-MCA bypass, hyperperfusion syndrome, radial artery graft, rescue revascularization
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.
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.
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.
21.4.1 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.
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.
The selected patients have redeveloped ischemic symptoms, although they have benefitted from initial STA- MCA bypass (symptom-free). Imaging studies demonstrate the delayed STA-MCA graft occlusion with lack of collaterals formation.
The individual testing of platelet antiaggregation is needed preoperatively.
To prevent the bypass occlusion, dilatation of the graft vessel with hydrostatic pressure as a preparation and use of 3,000 units heparin when opening the anastomosis have to be remembered to perform.
The distal end of the radial artery graft should be shaped only slight fish mouthing for recipient vessel mismatch.
Bypass may be technically infeasible due to recipient vessel mismatch and high fragility of MMD vessels. Bypass graft may be occluded due to vasospasm and thrombosis (5-10%). There is a high risk for perioperative stroke because the patients are hemodynamically unstable (9.3%). Furthermore, there is a high risk for hyperperfusion syndrome, which is increased for MMD patients (16.7-28.1%) compared to patients with another occlusive disease (atherosclerotic disease) (3.7%).
The patients should be maintained under normotensive conditions (systolic blood pressure, 120-140 mm Hg) immediately after anastomosis and postoperatively. Postoperative careful observations at intensive care unit are needed, whether the patients show the symptoms such as headache, seizure, and focal neurological deficit which are suspected of hyperperfusion.
The patient is positioned supine and the head is rotated 30 degrees off the vertical axis. The head skin incision is made behind the hairline from the midline to the zygomatic process. Frontotemporal craniotomy is performed, which expanded the initial craniotomy, if necessary. The cervical skin incision where the carotid bifurcation is also outlined (Fig. 21.1).
The position of the radial artery of the forearm is marked (Fig. 21.2). Radial artery is harvested in a typical manner. The graft vessel is dilated with controlled hydrostatic pressure and checked for leakage (Fig. 21.3).
M3 portion of the MCA is observed carefully whether it is suitable for use as a recipient artery. The arachnoid around the recipient artery (M3) is opened (Fig. 21.4).
If M3 portion is not suitable for recipient artery, M2 portion is selected. The sylvian fissure is gently opened to approach the M2 portion of the MCA (Fig. 21.5).
The radial artery graft is passed subcutaneously from the craniotomy incision to the cervical incision, and the proximal end of graft is prepared. The arteriotomy of the ECA is created with the aortic punch (Fig. 21.6). The first anastomosis is performed between the proximal end of the graft vessel and the ECA, just distal to the bifurcation of the common carotid artery (CCA) in end-to-side technique with 7-0 nylon threads. One side of the anastomosis is performed and the lumen is inspected (Fig. 21.7). The first anastomosis is completed (Fig. 21.8).
After distal end of the radial artery is prepared, the arteriotomy of M3 portion is created (Fig. 21.9). The second anastomosis is performed between the distal end of the graft vessel and the M3 portion in end-to-side technique with 10-0 nylon threads (Fig. 21.10). The second anastomosis is completed (Fig. 21.11).
The radial artery graft is anastomosed to the M3 portion of the MCA with careful attention to avoid graft kinking and distortion in overview of the craniotomy site (Fig. 21.12). The patency of the graft vessel is confirmed by intraoperative ICG angiography (Fig. 21.13) and quantitative Doppler flow measurements (Fig. 21.14).
• Meticulous surgical manipulation should be performed because the recipient vessel has high fragility.
• Enough orifice of recipient artery which fits the caliber of radial artery graft should be made.
• To avoid the thrombosis of anastomotic site, the proximal anastomosis should be performed first, and the use of heparin while opening the anastomosis has to be remembered.
Intraoperative bypass occlusion is a serious complication. The graft vessel should be dilated with controlled hydrostatic pressure for preparation to prevent the vasospasm and thrombosis. If the occlusion of anastomostic site is occurred, local injection of heparinized saline should be tried to perform first. If this method is not effective, reopening which followed by resuture of anastomotic site with careful inspection or remove and replace of graft vessel have to be done.
• There is the tendency for vasospasm and easy thrombosis of radial artery graft; therefore, the graft should be handled carefully.
• Quality of radial artery graft is usually sufficient even if MMD.
• Starting with proximal anastomosis is recommended for preventing of thrombosis at anastomotic site.
• There is the potential high risk of hyperperfusion; therefore, more distal recipient artery should be selected.
• Doppler flow measurements are needed for checking of graft patency.
• When the flow rates by the Doppler measurements are very high (up to 100 mL/min), it should be paid attention to the high possibility of hyperperfusion.
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