7.1 History and Initial Description

Surgical approaches with direct external carotid to internal carotid bypass operations to treat moyamoya patients were introduced in the early 1970s by Kikuchi and Karasawa ¹ in Japan and Krayenbühl ² in Europe with the intention of providing additional blood supply to hypoperfused vascular territories. Despite initial successes with this technique, a direct bypass depends on patency and suitability of both donor and recipient vessels. In moyamoya patients, often the recipient or donor arteries are either small or fragile and pose significant challenges for direct vasculary anastomosis; this is true in pediatric as well as adult patients. In 1964, Tsubokawa et al, reported successful cerebral revascularization in a 6-year-old female patient with use of a dural autograft containing the middle meningeal artery (MMA). Almost a decade later, Ausman et al reported the development of spontaneous anastomotic connections between the scalp and the cortical surface following direct superficial temporal artery (STA) to middle cerebral artery (MCA) bypass. Subsequent attempts at revascularization without a direct anastomosis led to the development of the encephalo-duro-arterio-synangiosis (EDAS) technique for the treatment of pediatric patients with moyamoya disease published by Matsushima et al in 1979. In 1980, Spetzler et al ³ were the first to report an “alternative method” for revascularization of the MCA, in which the STA was sutured to the cortical arachnoid in adults “in whom no adequate cortical recipient could be found.” Subsequent angiography demonstrated neovascularization and the patient remained neurologically intact postoperatively. Since then, numerous authors ^{4 – 8} have reported good clinical results with the use of EDAS in adults with moyamoya.

7.2 Indications

EDAS surgery is indicated for the management of all adult patients with intracranial arterial steno-occlusive disorders who present with symptoms of transient ischemic attack (TIA) or stroke in the territory of the affected vessel despite optimal medical management with antiplatelet agents. In our institution, and in a large number of centers in the United States, EDAS is the first choice of revascularization for any patient with intracranial arterial steno-occlusive disorders. For patients who have suffered stroke to be eligible for surgery, they need to have either functional independence (modified ranking scale < 3) or perfusion studies demonstrating tissue at risk for further ischemic damage in the territory of the stenoses. The diagnoses of the steno-occlusive disorder for which EDAS is indicated include:

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  Moyamoya disease defined as bilateral stenoses of the terminal internal carotid artery and proximal anterior cerebral artery (ACA) or MCA, with different degrees of angiographically evident lenticulostriate, leptomeningeal, or dural collaterals, in patients without risk factors for intracranial atherosclerosis, vascular dissection, or vasculitis.

  
  
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  Probable moyamoya disease defined as unilateral findings suggestive of moyamoya—as described above—in patients without risk factors for intracranial atherosclerosis, vascular dissection, or vasculitis.

  
  
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  Intracranial atherosclerosis defined as intracranial arterial disease with evidence of vessel wall calcification plus atherosclerotic risk factors, including history of hypertension, dyslipidemia, diabetes mellitus, smoking, and/or coronary or peripheral vascular atherosclerotic disease, failing intensive medical management with antiplatelets, statins, and risk factor reduction may benefit also from indirect EDAS revascularization. ⁵

7.3 Key Principles for the EDAS Surgery in Adults

Candidate patients for EDAS surgery are at risk for stoke during the perioperative period, both in the vascular territory to be treated and the contralateral hemisphere, if there is bilateral involvement. To reduce the risk of ischemic events associated with artery-to-artery embolisms, we recommend performing the operation under continuous antiplatelet therapy with aspirin. To reduce the risk of ischemia due to hypoperfusion, strict management of the patient’s blood pressure and fluid balance status must be maintained.

A successful EDAS is most dependent on scrupulous surgical technique. As the patients continue antiplatelet therapy throughout the procedure, meticulous hemostasis needs to be achieved while balancing avoidance of excessive cauterization of the arterial cuff, dura mater, or any other tissue that is used as a donor angiogenesis. Fastidious surgical technique can further minimize vasospasm and tissue injury, thus preventing intra- and postoperative complications. Finally, to facilitate the desired intracranial angiogenesis, donor arteries are positioned and fixed in close proximity to the pial surface while avoiding excessive arterial cuffs, tissue injuries, or bleeding.

As patients remain at risk for untoward events during and after surgery, the intraoperative anesthesia and postoperative critical care management are crucial to prevent stroke in adults undergoing EDAS. A detailed description of the anesthesia management is provided elsewhere. ²⁹ In brief, the goals of management include strict control of: (1) blood pressure, (2) fluid balance, (3) cerebral vascular reactivity, (4) platelet aggregation, (5) hematocrit, and (6) oxygenation. Some aspects of this management can seem unusual for a standard neurosurgical case; particularly the need to maintain a sufficiently high blood pressure at all times to avoid cerebral hypoperfusion in the territory of the stenosis may be overlooked with devastating consequences. Close coordination between the anesthesiologist and surgeon is therefore indispensable.

It is important to keep in mind that the surgery itself merely provides the starting point for revascularization, which may take several weeks to occur. Consequently, the perioperative care requires as much diligence as the surgical procedure. This includes continued adherence to anesthesia management goals in the immediate postoperative period until a stable and sufficient systolic blood pressure is reached. Thereafter, continued adherence to strict medical management is the key to obtain good clinical outcomes in adult patients undergoing EDAS.