Moyamoya Disease: Understanding the 6 Stages and Their Key Symptoms
Dealing with illness can be both physically exhausting and emotionally overwhelming. The burden becomes even greater when facing a rare or complex condition that isn't widely understood—even some healthcare professionals at smaller clinics may not recognize it. One such disorder is Moyamoya disease, a rare cerebrovascular condition that affects blood flow to the brain and often goes undiagnosed for years.
What Is Moyamoya Disease?
Moyamoya disease, also known as moyamoya syndrome or cerebrovascular occlusive disease, is characterized by the progressive narrowing or blockage of major arteries at the base of the brain—particularly the internal carotid arteries. As these vital vessels become obstructed, the brain attempts to compensate by forming tiny, fragile collateral blood vessels. On imaging scans, these abnormal networks resemble a "puff of smoke," which in Japanese is referred to as "moyamoya"—hence the name.
This condition develops slowly over time and is classified into six distinct stages based on the progression of vascular changes. Recognizing the symptoms at each stage is crucial for early diagnosis and effective management.
The Six Stages of Moyamoya Disease Explained
Stage 1: Terminal Internal Carotid Artery Stenosis
In the earliest phase, there are typically no noticeable symptoms. The primary change occurs at the end of the internal carotid artery, where mild narrowing begins. Because the brain still receives adequate blood supply through normal channels, patients may remain asymptomatic. This makes early detection challenging without specific imaging tests like MRI or angiography.
Stage 2: Formation of Moyamoya Vessels
As the disease progresses, the brain starts generating small collateral vessels to bypass the blocked areas. During this stage, patients may begin experiencing transient ischemic attacks (TIAs), often described as mini-strokes. Common signs include recurring headaches, dizziness, blurred vision, and episodes of confusion. These warning signals should never be ignored, as they indicate reduced cerebral perfusion.
Stage 3: Worsening Arterial Narrowing and Increased Collateral Vessel Growth
At this point, the internal carotid artery continues to narrow, and the obstruction begins affecting critical branches such as the middle and anterior cerebral arteries. The network of moyamoya vessels becomes more prominent on imaging studies. Patients frequently suffer from repeated ischemic events, including speech difficulties, weakness on one side of the body (hemiparesis), and sensory disturbances. Seizures may also occur in some individuals.
Stage 4: Early Decline of Moyamoya Vessels with Development of Extracranial Collaterals
The fragile moyamoya vessels start to regress due to chronic stress and poor functionality. However, the body adapts by developing new collateral pathways from external sources—such as branches from the scalp and facial arteries—that extend into the brain. While this extracranial-to-intracranial circulation helps maintain blood flow, it remains vulnerable to rupture or inefficiency under increased demand.
Stage 5: Reduction of Moyamoya Vessels and Risk of Infarction
There's a significant decrease in the number of native moyamoya vessels. Blood flow through the circle of Willis deteriorates further, with possible involvement of the posterior cerebral arteries. To compensate, the external carotid system takes on a larger role in supplying oxygenated blood. Unfortunately, this stage carries a high risk of ischemic stroke or cerebral infarction due to unstable perfusion and limited reserve capacity.
Stage 6: Complete Occlusion of the Internal Carotid System
This is the most advanced stage of Moyamoya disease. The internal carotid artery system is fully blocked, and the original moyamoya vessels have disappeared entirely. The brain now relies solely on collateral circulation from the external carotid arteries for survival. At this point, any disruption in blood flow—such as sudden drops in blood pressure or clot formation—can lead to devastating strokes or neurological deficits.
Why Early Detection Matters
Early intervention can significantly improve outcomes. In the initial stages, when symptoms are mild or absent, timely diagnosis allows for medical monitoring and potentially surgical revascularization procedures like EDAS (encephaloduroarteriosynangiosis) or EMS (encephalomyosynangiosis). These surgeries aim to restore blood flow and reduce the risk of future strokes.
Because Moyamoya disease progresses silently, anyone experiencing unexplained neurological symptoms—especially children with recurrent headaches or adults with TIAs—should consider a comprehensive cerebrovascular evaluation. Awareness and prompt action are key to preserving brain function and improving long-term prognosis.
Living With Moyamoya: A Call for Awareness
Though rare, Moyamoya disease poses serious health risks if left untreated. Public education, better diagnostic tools, and access to specialized neurovascular care are essential in managing this condition effectively. By understanding the six stages and their clinical implications, patients and doctors alike can work together to catch the disease early and implement life-saving treatments.