6.1 History and Initial Description

Indirect procedures for moyamoya syndrome tend to be reserved for pediatric patients where there is more successful collateralization, when compared with direct revascularization and where direct procedures are difficult due to the small size of the arteries. Indirect procedures include encephalo-myo-synangiosis, encephalo-galeo-myo-synangiosis, encephalo-duro-arterio-synangiosis, pial synangiosis, omental transplant (encephalo-omental synangiosis), and multiple burr holes. All are based on the observation that vascularized tissue placed on the brain induces vascular collateralization from the graft to the brain. Encephalo-duro-arterio-synangiosis (EDAS) involves the use of the dura and a branch of the superficial temporal artery (STA) to revascularize the brain. Originally described by Matsushima, the technique uses a branch of the STA to revascularize the brain by suturing the vessel in between two leaves of dura. A variant of this procedure, pial synangiosis, was developed by R. Michael Scott and differs by (1) affixing the STA to the brain surface with pial sutures and (2) widely opening the arachnoid to facilitate ingrowth of new vessels in response to growth factors elaborated by the ischemic brain. Pial synangiosis has become widely used in the pediatric population in the United States.

6.2 Indications

With caveats, the analysis from American Heart Association (AHA) concluded that “the data from the medical literature suggest that surgical revascularization is a safe intervention for pediatric moyamoya syndrome and most treated patients derive some symptomatic benefit.” The authors offer revascularization for patients with radiographic evidence of moyamoya, as defined by Suzuki grade II-VI on angiogram (or comparable findings on magnetic resonance angiogram/computed tomography angiogram [MRA/CTA] in the rare cases when catheter angiography is not possible), typically coupled with evidence of diminished or limited brain perfusion (most commonly the presence of “ivy sign”—hyperintense sulcal signal on axial fluid-attenuated inversion recovery (FLAIR) MRI, but also with evidence from other perfusion studies when necessary). This radiographic evidence is paramount, but clinical examination is important for decision making. Symptomatic patients are usually offered surgical treatment, but asymptomatic children are also operated if the imaging findings indicate severe perfusion deficits or progression of disease over time. In contrast, contraindications to surgery include evidence of preexisting neurologic devastation or very early disease (Suzuki I or II without perfusion problems) in an asymptomatic patient.

Surgical procedure selection is predicated on the symptom presentation, patient age, and anatomy. In most cases, there is a predilection to choose pial synangiosis over direct bypass, because of the data supporting the long-term durability of these grafts, and the ability to offer this operation to any age group. In patients without suitable vessels, myosyangiosis (using temporalis muscle) or pericranium with dura are suitable alternatives. Direct bypass is typically reserved for patients with vessels large enough for anastomosis (often teens or older), coupled with acute presentation of rapidly progressive strokes.

Regarding timing, the general principle of minimizing the time between diagnosis and revascularization is supported.

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  Delays may be reasonable to schedule experienced anesthetic/intensive care unit (ICU).

  
  
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  Medical contraindications may mandate delays (such as recent infarction, infection, or hemorrhage) (Class IIb C).

6.3 Key Principles

The surgical technique of EDAS is unique in the focus on creating a direct connection between the recipient brain and donor tissue. This principle is best exemplified by the most common subtype of EDAS used in the United States for children, pial synangiosis. In this procedure, an indirect anastomosis of the parietal branch of the superficial temporal artery is made to the cerebral cortex. Like other indirect operations, it also benefits from the recruitment of collateral vasculature from adjacent tissue, such as the dura and middle meningeal vessels. It differs from other EDAS procedures because pial sutures and the aggressive approach of a wide arachnoidal opening are used. The principle of the pial sutures rests on the concept that the normal pulsatile nature of the brain and donor vessel might inhibit growth of new vasculature, but suturing them together reduces relative motion and facilitates better growth.

The wide arachnoidal opening is perhaps the biologically most important aspect of the surgery, as recent data have revealed the significant role of angiogenic growth factors in the spinal fluid and embedded in the extracellular matrix of the pia as contributors to new vessel growth. Opening the arachnoid offers the double benefit of removing a mechanical barrier to ingrowth while also facilitating improved contact between nascent vasculature and growth factors.

6.4 SWOT Analysis

Assessment of EDAS using SWOT analysis is summarized below.

Related posts:

4 Multiple Burr Holes 8 Bifrontal Encephalo-duro-periosteal-synangiosis Combined with STA–MCA Bypass 5 Encephalo-myo-synangiosis 7 Encephalo-duro-arterio-synangiosis: In Adults 11 Occipital Artery–Middle Cerebral Artery Bypass in Moyamoya Disease 16 Combined Direct (STA–MCA) and Indirect (EDAS) EC–IC Bypass

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