Moyamoya disease (MMD) is a rare, progressive cerebrovascular condition affecting the arteries supplying blood to the brain. The disorder is defined by the gradual narrowing and eventual blockage of major vessels located at the base of the skull. The name “Moyamoya” originates from a Japanese phrase meaning “a puff of smoke,” describing the appearance of tiny, abnormal blood vessels that form in response to the blocked circulation. Reduced blood flow can lead to devastating neurological events, including strokes and brain hemorrhage. Management requires specialized and timely intervention to stabilize blood flow and limit long-term brain damage.
Defining the Condition
The core pathology involves the progressive constriction (stenosis) of the terminal portions of the internal carotid arteries (ICAs). These two large vessels supply the anterior two-thirds of the brain with oxygenated blood. The narrowing typically extends into the proximal branches of the ICAs, specifically affecting the anterior and middle cerebral arteries. This blockage severely compromises the brain’s main blood supply, leading to chronic cerebral ischemia (insufficient blood flow).
In response to reduced blood flow, the brain attempts to compensate by developing a network of smaller, delicate collateral vessels. These fragile arteries sprout from the base of the brain, creating new pathways to bypass the primary blockages. While attempting to restore circulation, this collateral network is structurally weak and abnormally fragile. These vessels are susceptible to both rupture (causing bleeding) and thrombosis (contributing to further ischemic events).
Underlying Causes and Risk Factors
The precise cause of Moyamoya disease remains largely unknown in many cases, which are then categorized as Idiopathic Moyamoya Disease. Genetic factors are strongly implicated, especially in populations where the condition is more prevalent. Research has identified a significant association with a mutation in the RNF213 gene, particularly in people of East Asian descent. This genetic predisposition contributes to the higher incidence rates observed in countries like Japan, Korea, and China.
When the characteristic vascular changes occur in conjunction with another underlying medical condition, the disorder is classified as Moyamoya Syndrome. Several conditions increase the risk of developing this syndrome:
- Down syndrome
- Sickle cell disease
- Neurofibromatosis type 1
- Radiation exposure to the head and neck
The condition has a distinct bimodal age distribution, meaning it tends to be diagnosed most frequently within two separate age ranges. The first peak occurs in children, typically between 5 and 10 years of age. The second peak is seen in adults, most commonly in their 30s and 40s. Moyamoya disease affects females approximately twice as often as males.
Symptoms and Diagnostic Confirmation
Moyamoya disease presents with symptoms that stem from either insufficient blood flow to the brain (ischemia) or bleeding (hemorrhage). Ischemic events are the most common presentation in children, often manifesting as transient ischemic attacks (TIAs) or full strokes. These episodes frequently produce weakness, numbness, or paralysis, usually on one side of the body. They may be triggered by activities that cause hyperventilation, such as crying, exercise, or blowing up a balloon. Children may also experience developmental delays, cognitive impairment, or recurrent headaches.
Adults with the condition are more likely to present with hemorrhagic stroke, which involves bleeding from the fragile, compensatory vessels. This bleeding can cause sudden, severe headaches, seizures, and rapid neurological decline. Regardless of age, the symptoms are progressive and can lead to permanent neurological deficits if not managed effectively.
Confirmation of Moyamoya disease relies on specialized imaging techniques to visualize the cerebral vasculature. Magnetic Resonance Angiography (MRA) is often used initially to non-invasively assess the narrowing of the internal carotid arteries. The definitive diagnostic tool is Digital Subtraction Angiography (DSA), which provides high-resolution images of the blood flow dynamic. The presence of the characteristic stenosis in the ICAs combined with the “puff of smoke” collateral vessels on the angiogram confirms the diagnosis.
Management and Treatment Strategies
The primary goals of managing Moyamoya disease are to prevent future strokes and to improve the overall blood supply to the brain. Medical management is typically used as an adjunctive measure to control symptoms and reduce the risk of clot formation. Antiplatelet medications, such as aspirin, are often prescribed to thin the blood and help prevent blockages within the small, existing vessels.
Calcium channel blockers may be used to help manage severe headaches associated with the condition. However, medication alone does not halt the progressive narrowing of the arteries. Surgical revascularization is the mainstay of treatment for most patients with symptomatic Moyamoya disease.
Surgical procedures are designed to bypass the blocked arteries and restore adequate blood flow to the brain’s surface. These revascularization techniques are broadly divided into two categories: direct and indirect bypasses.
Direct Bypass
A Direct Bypass procedure, such as the Superficial Temporal Artery to Middle Cerebral Artery (STA-MCA) anastomosis, involves directly connecting a scalp artery to a brain artery. This technique immediately provides a new, high-flow pathway for blood to reach the brain. Direct bypass is often preferred for adults.
Indirect Bypass
Indirect Bypass procedures, like Encephaloduroarteriosynangiosis (EDAS), involve laying blood-rich tissue onto the brain’s surface. This does not provide immediate blood flow, but over several weeks or months, it encourages the growth of new blood vessels into the brain tissue below. Indirect methods tend to be highly effective in children due to their greater capacity for new vessel growth.