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

Unilateral moyamoya disease is a rare cerebrovascular disorder characterized by the progressive stenosis or occlusion of the internal carotid arteries and their major branches, primarily affecting one side of the brain. To restore cerebral blood flow and prevent ischemic events such as stroke, surgical intervention plays a crucial role. Modern treatment strategies focus on revascularization procedures that can be broadly categorized into direct and indirect techniques—each tailored to the patient's anatomy, age, and clinical presentation.

Direct Revascularization: Bypass Surgery for Immediate Blood Flow Restoration

Direct vascular bypass surgery is often recommended for patients with unilateral involvement who are good surgical candidates. This procedure involves creating a direct connection between an extracranial artery and an intracranial vessel to immediately improve blood supply to the affected hemisphere. The most common approach is the superficial temporal artery (STA) to middle cerebral artery (MCA) anastomosis, performed on the same side as the diseased vessels.

In cases where a higher volume of blood flow is required—such as in patients with significant hemodynamic compromise—a high-flow bypass may be considered. This typically involves using a graft, such as the saphenous vein or radial artery, to connect larger vessels like the external carotid artery to the MCA. High-flow reconstructions are particularly beneficial when the STA is too small or unsuitable for standard anastomosis.

Indirect Revascularization: Promoting Natural Collateral Formation

Unlike direct methods, indirect revascularization techniques do not create an immediate conduit for blood flow. Instead, they encourage the development of new collateral vessels over time through angiogenesis. These approaches are especially effective in pediatric patients but are also used in select adults.

Common Indirect Surgical Methods

One widely used technique involves creating a bone flap and then folding the dura mater inward so that its rich vascular network can gradually grow into the brain tissue. This process, known as dural inversion or encephaloduroarteriosynangiosis (EDAS), promotes neovascularization from the dural surface into the cortex.

Additional indirect methods include:

• Encephalomyosynangiosis (EMS): Placing the temporalis muscle directly onto the brain surface to stimulate vessel ingrowth.
• Encephaloduroarteriomyosynangiosis (EDAMS): A combined approach utilizing both dural and muscle tissues.
• Multiple burr holes with vascularized fascia: Drilling small holes in the skull and placing vascularized tissue grafts to initiate collateral formation.

These procedures rely on the body's natural healing response to establish alternative pathways for cerebral perfusion, typically showing significant improvement within 3–6 months post-surgery.

Choosing the Right Approach: Personalized Treatment Plans

The decision between direct, indirect, or combined revascularization depends on several factors including the patient's age, extent of arterial blockage, cognitive status, and risk of future stroke. Many neurosurgical centers now advocate for a hybrid approach, combining both direct bypass and indirect techniques during the same operation to maximize short- and long-term outcomes.

Postoperative imaging, such as MRI, MRA, or SPECT scans, is essential to monitor the development of collateral circulation and assess the success of revascularization. With proper surgical planning and follow-up care, patients with unilateral moyamoya disease can experience improved cerebral perfusion, reduced stroke risk, and enhanced quality of life.