Moyamoya Disease

You have been diagnosed with Moyamoya—what does this mean?

A diagnosis of Moyamoya means that the major arteries supplying the brain (the terminal segments of the internal carotid arteries and the origins of the middle and anterior cerebral arteries) are progressively narrowing or becoming occluded. To compensate, the brain forms a network of extremely thin, fragile collateral vessels— the characteristic “Moyamoya vessels.”

Without specialized treatment, the risk of recurrent ischemic or hemorrhagic stroke is high. With timely and appropriate revascularization, however, many children and adults can be effectively protected and maintain an active life.

What exactly is Moyamoya disease?

Moyamoya is an idiopathic (without an identifiable external cause) cerebrovascular disorder characterized by:

• Progressive stenosis or occlusion of the supraclinoid segments of the internal carotid arteries
• Involvement of the proximal middle and anterior cerebral arteries
• Hypertrophy and proliferation of small perforating arteries (lenticulostriate vessels)
• Formation of a new, fragile collateral network with the characteristic “smoky” appearance on angiography

The term Moyamoya syndrome is used when the same angiographic pattern occurs secondarily, for example after radiation therapy, in atherosclerosis, sickle cell disease, Down syndrome, NF-1, and other conditions.

Causes & heredity

Moyamoya is considered a multifactorial disease. Contributing factors may include:

• Genetic predisposition—familial occurrence in approximately 7–12% of cases in Japan
• Associations with Down syndrome, NF-1, and congenital heart disease
• Autoimmune disorders (thyroiditis, systemic lupus erythematosus, type 1 diabetes)
• Possible inflammatory and vascular remodeling mechanisms

Inheritance is not always straightforward. In families with a history of Moyamoya, screening of siblings or children with magnetic resonance angiography may be recommended after consultation with a specialized center.

What are the symptoms in children & adults?

Clinical presentation varies by age and by whether ischemia or hemorrhage predominates.

Children

• Transient weakness, numbness, or paralysis of the limbs
• Speech disturbances, difficulty finding words
• Recurrent “paroxysmal” episodes of weakness following crying, fever, or hyperventilation
• Seizures
• Headache, behavioral changes, or decline in school performance

Adults

• Ischemic stroke or transient ischemic attacks (more common in Western populations)
• Intracerebral or subarachnoid hemorrhage (more common in Asian populations)
• Headache, dizziness, difficulty concentrating
• Neuropsychological deficits in chronic ischemia

How is the diagnosis made & what is angiographic evaluation?

Diagnosis is based on a combination of clinical findings and advanced imaging:

• Brain MRI/MRA — identifies prior or new infarcts and major vessel stenosis.
• CTA (CT angiography) — rapid vascular imaging, useful in emergencies.
• DSA (Digital Subtraction Angiography) — the gold standard, demonstrating the classic “puff-of-smoke” collaterals and allowing Suzuki staging.
• Transcranial Doppler — adjunct for monitoring flow and dynamic changes.

In selected patients, hemodynamic studies (CT/MR perfusion, SPECT, PET) are performed to assess cerebrovascular reserve and guide surgical planning.

When is surgery required?

Moyamoya is generally a surgical disease—medications alone do not halt progression. Revascularization is recommended when:

• Ischemic events (TIA/stroke) or hemorrhage have occurred
• There is bilateral or advanced angiographic disease
• Imaging demonstrates reduced cerebrovascular reserve
• The patient is a child with typical Moyamoya, even with “mild” symptoms—because the risk of permanent injury is high

In asymptomatic adults with mild, unilateral disease, the decision is individualized after thorough multidisciplinary evaluation.

What are revascularization (bypass) procedures?

The goal of surgery is to create a new, reliable blood supply to the brain, reducing dependence on fragile Moyamoya vessels.

Direct revascularization

• STA–MCA bypass — the superficial temporal artery from the scalp is directly anastomosed to a cortical branch of the middle cerebral artery, providing immediate flow augmentation.

Indirect revascularization

• EDAS (encephaloduroarteriosynangiosis)
• EDAMS (with additional muscle flap)
• Multiple burr holes — multiple small craniostomies with angiogenic grafts, especially in children

Direct and indirect techniques are often combined to achieve both immediate and long-term protection.

How is the surgery performed & what should you expect during hospitalization?

Surgery is performed under general anesthesia with specialized neuroanesthetic monitoring of cerebral perfusion. General steps include:

• Small craniotomy over the region to be revascularized
• Preparation of the superficial temporal artery or other vascular graft
• Direct bypass to a cortical artery and/or placement of angiogenic tissue on the cortex
• Verification of flow using intraoperative ICG videoangiography
• Closure of bone and skin

Hospitalization typically lasts 3–5 days. In children, return to light activities occurs within 1–2 weeks, while full neovascularization from indirect bypass develops over 3–6 months. A second-stage procedure on the opposite side is often required.

What is recovery like & what is the long-term outlook?

International data and our own experience demonstrate that surgical revascularization significantly reduces the risk of subsequent ischemic or hemorrhagic events compared with conservative treatment.

Most patients:

• Remain free of major strokes for many years
• Experience improvement in endurance, concentration, and daily functioning
• Require long-term follow-up with clinical and imaging surveillance

Prognosis depends on age, the extent of pre-existing brain injury, and the timing of surgery— earlier intervention is associated with better outcomes.

Daily life, school, work & pregnancy

After successful revascularization, most children return to normal schooling and activities, with temporary restrictions on extreme sports or hyperventilation-provoking activities until revascularization is complete.

Adults can usually continue working, with adjustments depending on any pre-existing neurological deficits. Pregnancy is possible but should be carefully planned and monitored in collaboration with a specialized neurosurgical and obstetric team.

When should I seek urgent medical care?

Call emergency services immediately if any of the following occur:

• Sudden weakness or numbness of the face, arm, or leg
• Inability to speak or find words
• Sudden vision loss or double vision
• Seizures, loss of consciousness, or an unusually severe headache