Benefits and Risks of Encephalomyosynangiosis Surgery for Moyamoya Disease

Moyamoya disease is a rare cerebrovascular disorder characterized by the progressive narrowing of arteries at the base of the brain, leading to reduced blood flow and an increased risk of stroke. To restore cerebral perfusion, various surgical revascularization techniques have been developed. Among them, encephalomyosynangiosis (EMS), commonly known as temporal muscle grafting or indirect bypass, has been used for decades as a treatment option, particularly in pediatric cases.

What Is Encephalomyosynangiosis (Indirect Bypass)?

Encephalomyosynangiosis involves placing highly vascularized tissues—such as the temporalis muscle—directly onto the surface of the brain. The goal is to encourage the development of new collateral blood vessels over time, a process known as angiogenesis. Unlike direct bypass procedures that immediately reroute major arteries, EMS relies on the body's natural ability to form new vascular networks, which can take weeks to months to become functional.

Advantages of Temporal Muscle Grafting

One of the primary benefits of EMS is its relatively low surgical complexity compared to combined direct-indirect bypass techniques. It does not require microvascular anastomosis, making it a viable option in centers with limited neurosurgical expertise. Additionally, because no large vessel connections are made, there is less immediate risk of intraoperative complications such as thrombosis or hemorrhage. This makes EMS especially suitable for young children whose small vessel size makes direct bypass technically challenging.

Limitations and Risks of Indirect Revascularization

Despite its historical use, EMS has notable drawbacks, especially in adult patients. The most significant limitation is the delayed revascularization effect. Since new blood vessels develop gradually, patients remain vulnerable to ischemic events during the critical period before adequate collateral circulation forms. Clinical studies indicate that some patients may suffer recurrent strokes or transient ischemic attacks within the first three months post-surgery—before the grafted muscle fully promotes angiogenesis.

Why Combined Bypass Often Outperforms EMS

In contrast, combined direct- and indirect bypass surgery offers both immediate and long-term blood flow improvement. Direct bypass (such as STA-MCA anastomosis) instantly redirects blood from scalp arteries to the brain, while indirect methods like EMS support sustained vascular growth. For adult patients, who typically have less robust angiogenic potential than children, this dual approach leads to higher rates of successful revascularization and better clinical outcomes.

Furthermore, long-term follow-up data suggest that EMS alone may result in suboptimal neovascularization in a significant number of adult cases. The procedure's effectiveness depends heavily on individual biological factors, and when angiogenesis is insufficient, patients face ongoing risks of cognitive decline, seizures, or stroke recurrence.

Conclusion: Choosing the Right Surgical Approach

While encephalomyosynangiosis played a crucial role in the evolution of moyamoya treatment, modern neurosurgical practice increasingly favors combined revascularization strategies for most patients, especially adults. These approaches offer faster protection against ischemia and more reliable restoration of cerebral blood flow. As research advances, patient-specific factors—including age, disease stage, and vascular anatomy—are guiding more personalized treatment decisions, moving beyond one-size-fits-all solutions.