Pediatric Moyamoya Disease

You’ve been diagnosed with Moyamoya—what does that mean?

A Moyamoya diagnosis means the terminal segments of the internal carotid arteries and the central cerebral arteries are progressively narrowing. The brain attempts to compensate by creating a network of very small, fragile collateral vessels— the so-called “Moyamoya vessels.”

Some patients remain relatively stable for years, while others experience multiple strokes over weeks to months. Without specialized treatment, more than two-thirds of patients show clear clinical deterioration within the first 5 years.

What exactly is Moyamoya?

Moyamoya is a progressive, idiopathic arteriopathy affecting the intracranial internal carotid arteries and their proximal branches:

• Narrowing/occlusion of the supraclinoid internal carotid arteries, often bilaterally
• Involvement of the proximal anterior cerebral artery (ACA) and middle cerebral artery (MCA)
• Hypertrophy & neovascularization with proliferation of small perforator (lenticulostriate) vessels
• Formation of a “puff of smoke” collateral network at the brain’s base

The term Moyamoya disease is used when the condition is idiopathic and typically bilateral. Moyamoya syndrome refers to the same angiographic pattern occurring secondarily (e.g., after radiotherapy, in NF1, sickle cell disease, Down syndrome, etc.), sometimes presenting unilaterally.

Causes, genetics & associated syndromes

The precise cause is still being investigated, but the condition is associated with:

• Genetic factors—familial cases are reported in ~7–12% in some Asian populations. Variants in genes such as RNF213 (especially in patients of Asian ancestry) and ACTA2, among others, have been linked to Moyamoya.
• Syndromes & comorbid conditions—Down syndrome, neurofibromatosis type 1, sickle cell anemia, congenital heart disease, vasculitides, and prior cranial irradiation.
• Vascular and inflammatory mechanisms—smooth muscle hyperplasia within vessel walls, endothelial dysfunction, and inflammatory pathways are implicated.

This is not a single-gene condition; it is better viewed as a spectrum of pathways that converge on the same outcome: progressive stenosis and a reliance on fragile collateral circulation.

How does it present—symptoms in children

Most patients (60–90%) develop ischemic symptoms, though seizures, headaches, or hemorrhage can also occur.

• Transient weakness or paralysis of an arm/leg (TIA)
• Sudden speech difficulty or trouble understanding language
• Recurrent episodes triggered by crying, fever, or hyperventilation
• Seizures
• Headaches, behavioral changes, or a decline in school performance

Natural history & risk without treatment

Without surgical revascularization, Moyamoya is considered almost always progressive:

• More than two-thirds of patients show clear clinical deterioration within 5 years of diagnosis.
• Repeated ischemic events can lead to cumulative neurological disability.

In contrast, revascularization surgery has been associated with a substantial reduction in stroke risk (for example, a 5-year risk decreasing from ~66% to ~4% in pediatric cohorts).

When is surgery recommended?

Internationally—and in our own practice—revascularization is typically recommended when there is:

• Recurrent clinical ischemic events (TIA or stroke)
• Evidence of reduced cerebral perfusion or impaired cerebrovascular reserve on flow studies
• Advanced angiographic stage (Suzuki II–VI)
• Radiologic progression on serial MRI

Japanese and U.S. guidance aligns: for patients with clear ischemic symptoms or markedly reduced flow reserve, revascularization should be considered—provided there are no major contraindications to surgery.

In asymptomatic, early, unilateral cases, the decision is more individualized and should be discussed in a specialized multidisciplinary setting.

How is the diagnosis confirmed? Which tests are needed?

Moyamoya diagnosis is based on clinical presentation and key angiographic criteria (as described in Japanese diagnostic frameworks):

• Narrowing/occlusion of the terminal ICAs and proximal ACA/MCA
• Presence of dilated basal collateral networks (“Moyamoya vessels”)
• Often bilateral involvement

Core diagnostic tests include:

• CT / CTA—useful in urgent settings, especially to assess hemorrhage
• MRI / MRA—demonstrates ischemia, degree of stenosis, and signs such as the “ivy sign”
• DSA (catheter angiography)—the gold standard; typically includes 6-vessel evaluation (ICAs, ECAs, VAs), Suzuki staging, and assessment of spontaneous collateral pathways (STA, MMA, etc.)
• Perfusion/flow studies—SPECT with acetazolamide, CT/MR perfusion, ASL, TCD, as indicated

In selected cases, additional laboratory/genetic testing may be appropriate (RNF213, ACTA2, vasculitis evaluation, aspirin response testing, etc.).

Types of revascularization—direct & indirect bypass

The goal of surgery is to create a new, reliable blood supply route from external carotid system branches (or, less commonly, other graft sources) to the underperfused brain.

Direct revascularization (direct bypass)

• STA–MCA bypass—the superficial temporal artery (in the scalp) is dissected and directly anastomosed to a cortical MCA branch. It provides immediate flow augmentation but requires advanced microsurgical skill, particularly in small children.

Indirect revascularization (indirect bypass)

• EDAS – encephaloduroarteriosynangiosis
• EMS / EDAMS – with incorporation of the temporalis muscle
• Dural inversion – turning vascular dura onto the brain surface
• Multiple burr holes – multiple small openings with placement of angiogenic flaps

Indirect techniques rely on angiogenesis: the placed tissues act as an “angiogenic scaffold,” and over months, the brain develops a more stable collateral network.

The operation & what to expect during hospitalization

Surgery is performed under general anesthesia, with specialized neuro-anesthesia and careful management of blood pressure and cerebral perfusion.

Typical steps (illustrative for pial synangiosis + indirect bypass):

• Planning the incision and craniotomy over the at-risk territory
• Careful dissection of the STA and its branches
• Small craniotomy and opening of the dura
• Microsurgical anastomosis of the STA to a cortical vessel under the microscope (fine sutures such as 10-0)
• Placement of vascularized flaps (artery, dura, muscle) onto the cortical surface
• Flow confirmation with ICG video angiography & Doppler
• Layered closure and hemostasis

Hospital stay is commonly 3–5 days, with close monitoring of blood pressure, hydration, CO₂ levels (avoiding hyperventilation), and neurological status. In bilateral disease, a second-stage procedure to revascularize the opposite hemisphere is often planned at a separate time.

Recovery & long-term outlook

Recovery depends on pre-existing injury and age. Children with minimal events before revascularization generally have the best outcomes.

• Return to light activities within 1–2 weeks
• Full indirect-bypass angiogenesis typically develops over 3–6 months
• Annual (or semiannual) MRI/MRA and clinical follow-up
• Across many series, surgical revascularization markedly reduces the risk of future stroke compared with medication alone.

Long-term surveillance helps detect progression elsewhere or identify the need for additional treatment early.

Daily life, school, work & pregnancy

Our goal is not only stroke prevention, but enabling a as-normal-as-possible life.

• Children: return to school with appropriate support; avoid dehydration and extreme fatigue; tailor sports participation case-by-case.
• Teens/adults: adjust work as needed based on neurological status; avoid intense hyperventilation and significant dehydration.
• Pregnancy: often feasible, but should be planned and monitored in collaboration with an experienced neurosurgical and obstetric team.

Most patients—after successful revascularization and appropriate follow-up—go on to live active, meaningful lives.