14.1 History and Initial Description

In 1977 Karasawa et al published the first description of encephalo-myo-synangiosis (EMS) in moyamoya patients showing that in combination with direct superficial temporal artery–middle cerebral artery (STA–MCA) anastomosis novel collateral vessels develop on the surface of the brain supplied by the deep temporal artery that is known to deliver blood flow to the temporal muscle. ¹ The introduction of this indirect revascularization procedure for moyamoya patients initiated an ongoing debate about the ideal revascularization strategy leading to the development of various combined revascularization protocols. Matsushima et al demonstrated that combined STA–MCA bypass and EMS is superior to indirect only procedures regarding development of collateral blood flow and clinical improvement of ischemic patients. ^{2 ,​ 3} Age-dependent revascularization patterns revealed that in adult patients STA–MCA anastomosis is the main source of additional blood flow in the case of combined STA–MCA/EMS surgery, whereas in pediatric patients collateral flow via the EMS significantly improves over the course of time compensating or even replacing blood flow via the direct anastomosis. ⁴ Functional analysis demonstrates that in adult patients combined STA–MCA/EMS leads to a significant recovery of cerebrovascular reserve capacity while single EMS does not lead to reversal of hemodynamic compromise. ⁵ Therefore, combining STA–MCA anastomosis with EMS is especially beneficial in pediatric patients whereas the additional application of EMS seems of inferior importance in adult patients in the presence of a direct anastomosis.

14.2 Indications

Combined STA–MCA bypass and EMS is used in pediatric patients and young adults as the revascularization strategy of choice. In pediatric patients EMS has been demonstrated to lead to successful revascularization results and may represent an important additional source of collateral flow in case of small STA size and insufficient direct bypass function. In adults, EMS demonstrates less effective revascularization results and is primarily performed additionally to STA–MCA bypass in case of small or insufficient STA anatomy.

14.3 Key Principles

The general concept of combining STA–MCA bypass and EMS in moyamoya patients includes the idea that more blood flow is restored in a larger vascular territory of the brain via the combined strategy as compared to either single procedure. Additionally, the combination of both procedures promises maintenance of collateral flow in the case of failure of a single procedure (reciprocal compensation).Sufficient platelet antiaggregation is recommended depending on preoperative assessment of aspirin resistance using PFA-100 testing. ⁶ Compared to single STA–MCA bypass surgery, the size of the craniotomy is increased to the size of the temporal muscle (with the sylvian fissure as the center of craniotomy) in order to allow transposition to the brain surface. Special care has to be applied to preparation of the galea and the base of the temporal muscle in order to avoid damage to the neovascular potential of the donor tissue. This includes avoidance of compression at the base of the temporal muscle especially after bone flap reimplantation in order to avoid both compression of the donor branch of the STA and the blood supply of the temporal muscle.

14.4 SWOT Analysis

14.5 Contraindications

Presence of middle meningeal artery (MMA) as part of vault moyamoya vessels or the STA as contributor of vault moyamoya vessels represent the most important contraindications. The required large dural opening imposes a significant risk for dural feeders of vault moyamoya vessels potentially leading to cerebral ischemia. As combined STA–MCA/EMS revascularization is predominantly used for pediatric patients, an insufficient caliber of the STA may be a relevant disadvantage and often represents a technical challenge for the surgeon. Nevertheless, direct anastomosis is recommended in the presence of a potentially useful donor vessel. Massive brain atrophy also represents a special contraindication as physical contact between the temporal muscle and the brain surface (brain/muscle interface) is required for successful indirect revascularization. As the temporal muscle is sutured to the dural edges, brain atrophy may increase the distance between the dura and brain surface making physical contact between muscle and brain surface impossible.

14.6 Special Considerations

Vascular imaging modalities represent the most important prerequisite to plan STA–MCA/EMS revascularization. Digital subtraction angiography should focus apart from the intracranial vascular status on the external carotid artery to visualize presence, size and course of the STA. Special attention has to be paid to vault moyamoya vessels, their specific contributors (i.e., occipital artery, MMA, STA, etc.) and localization. It is especially important to analyze vault moyamoya vessels in anteroposterior and lateral views in order to judge their contribution of collateral blood flow to the brain. Presence of vault moyamoya vessels fed by the MMA may either be a contraindication for this surgical strategy or it may lead to a different surgical technique for establishing EMS by opening the dura around the MMA in order to protect collateral flow via the extraintracranial anastomoses. MRI represents another important aspect not only to rule out signs of acute ischemia but also to judge brain atrophy. Major brain atrophy may represent an important obstacle making it impossible to establish a sufficient brain/muscle interface. Anticoagulation is usually established preoperatively using aspirin 100 mg orally once daily. Platelet antiaggregation is tested preoperatively using PFA-100 testing in order to rule out aspirin resistance. In the presence of aspirin resistance, the daily dose is increased to 300 mg orally, followed by PFA-100 retesting. If aspirin resistance cannot be overcome by increasing the daily dose to 300 mg, antiaggregation strategy is changed to clopidogrel 75mg daily. In this case, surgery is then performed under clopidogrel 75 mg. It must be mentioned that other institutions deal differently with preoperative antiplatelet therapy. Some surgeons do not even perform any antiplatelet therapy before or directly after bypass surgery. Therefore, the above named antiplatelet strategy represents a recommendation in the lack of high-level evidence regarding antiplatelet therapy in moyamoya vessel patients. In the following chapters technical descriptions of each revascularization strategy include the authors’ preferred antiplatelet strategy during revascularization surgery therefore a broad overview will be provided.

The anatomic specificities of the individuals STA govern the shape of the skin incision. Depending on which STA branch is used as donor vessel, a Y-shaped or a curved skin incision is used to prepare the donor vessel as well as the temporal muscle.

Special surgical care has to be applied to preparation of the temporal muscle and the galea apart from preparation of the STA, as the sacrifice of the STA and the staged preparation of the skin and temporal muscle may lead to problems with wound healing. Therefore, a clear concept for the skin incision as well as muscle preparation should be followed in order to minimize surgical trauma to these tissues (Fig. 14‑1). Blunt dissection of the temporal muscle from the underlying bone is performed starting from the base of the temporal muscle with stepwise dissection toward the temporal line in order to maintain structural and vascular integrity of the muscle surface. Preparation of the temporal muscle imposes an ambivalent problem as bipolar or monopolar coagulation should be avoided to protect microvascular integrity; on the other side, bleeding sources should be addressed as the surface of the temporal muscle may represent a source for postoperative hemorrhages, especially subdural hematomas. Moreover, sensitive handling of the muscle is important in order to reduce the risk for muscle edema, which may lead to compression of the cerebral surface after establishing the brain/muscle interface. As the deep temporal artery courses along the base of the temporal muscle, avoid dissection of the basal part in order to protect blood supply. The craniotomy is centered around the sylvian fissure and its individual size and shape is orientated on the shape and size of the temporal muscle before dissection is started.