Surgical Approaches for Moyamoya Disease: Understanding Direct and Indirect Revascularization Techniques

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. As the condition advances, patients may experience transient ischemic attacks (TIAs), seizures, or cognitive decline. To prevent long-term neurological damage, surgical intervention is often necessary. Among the most effective treatments are revascularization procedures, which aim to restore adequate blood supply to the brain. These surgeries fall into two primary categories: direct bypass and indirect revascularization.

Direct Surgical Bypass: Immediate Restoration of Blood Flow

Direct revascularization, also known as extracranial-to-intracranial (EC-IC) bypass surgery, involves connecting a healthy blood vessel from outside the skull—typically the superficial temporal artery—to a targeted cortical artery within the brain. This surgical technique creates an immediate and reliable pathway for oxygen-rich blood to reach ischemic regions of the brain. By directly bridging the external and internal circulatory systems, this method provides rapid improvement in cerebral perfusion, making it particularly beneficial for patients with severe or rapidly progressing symptoms.

One of the key advantages of direct bypass is its predictable and measurable outcomes. Postoperative imaging often confirms successful graft patency and enhanced blood flow, which correlates with symptom relief and a lower risk of future strokes. For eligible patients—especially those with good overall health and suitable vascular anatomy—direct surgery is generally considered the preferred option due to its superior efficacy in preventing ischemic events.

Indirect Revascularization: Encouraging Natural Vessel Growth

In contrast, indirect revascularization techniques do not create an instant connection between external and internal vessels. Instead, these procedures involve placing vascularized tissues—such as the temporalis muscle, dura mater, or galea aponeurotica—onto the surface of the brain. Over time, new collateral vessels gradually form between the transplanted tissue and the cerebral cortex through a process called angiogenesis.

Common Indirect Procedures Include:

• Encephaloduroarteriosynangiosis (EDAS): The superficial temporal artery is sutured onto the dura to encourage vessel ingrowth.
• Encephalomyosynangiosis (EMS): The temporalis muscle is laid over the brain surface to promote neovascularization.
• Dural inversion or multiple burr holes: These stimulate localized blood vessel development.

While indirect methods are less invasive and can be safer for younger patients or those with fragile vasculature, their effects are slower to manifest—often taking weeks to months. Additionally, the degree of revascularization can vary significantly between individuals, making outcomes less predictable than with direct bypass.

Choosing the Right Surgical Strategy

The decision between direct and indirect surgery depends on several factors, including the patient's age, disease stage, cerebrovascular reserve, and anatomical feasibility. In adult patients with sufficient vessel size and stability, direct bypass is typically favored for its immediate benefits and strong clinical evidence. However, in pediatric cases or when donor vessels are too small for direct anastomosis, indirect techniques offer a viable alternative that still supports meaningful recovery.

Increasingly, many neurosurgical centers adopt a combined approach, performing both direct and indirect procedures during the same operation to maximize short- and long-term revascularization. This hybrid strategy leverages the instant results of direct bypass while promoting sustained vascular growth through indirect mechanisms.

In conclusion, surgical treatment for moyamoya disease has evolved into a highly effective intervention that can dramatically reduce stroke risk and improve quality of life. While direct revascularization offers more consistent and immediate results, indirect methods remain valuable tools, especially in complex or high-risk cases. A personalized treatment plan, developed by a multidisciplinary team, ensures optimal outcomes tailored to each patient's unique condition.