Overview
Moyamoya disease is a chronic, progressive cerebrovascular condition where certain arteries at the base of the brain, particularly the internal carotid arteries, become narrowed or blocked for unknown reasons. This blockage leads to the formation of small, abnormal blood vessels known as ‘moyamoya vessels’ to compensate for reduced blood flow.Medical Field
This disease is commonly managed by the neurosurgery department.Definition
Moyamoya disease primarily affects the internal carotid arteries, specifically where they branch into the anterior and middle cerebral arteries. Narrowing or blockage in these areas leads to the development of moyamoya vessels, which resemble wisps of smoke on imaging studies. The condition usually affects both carotid arteries, though in about 10% of cases, only one side is impacted, referred to as unilateral moyamoya disease.First described in 1957 by Takeuchi and Shimizu, the name ‘moyamoya’ was coined by Suzuki in 1969, as the appearance of the abnormal blood vessels on imaging resembled ‘a puff of smoke’ in Japanese.
Moyamoya disease occurs more frequently in East Asia, particularly in Japan and South Korea, where the incidence is 10 times higher than in Western countries. It is more common in women, occurring at about twice the rate in men. Around 15% of cases show a family history, and genetic factors are suspected, especially in twins where one affected sibling significantly increases the risk for the other.
Though there are no comprehensive statistics for South Korea, an estimated 600 cases were reported in medical literature up until 1995. The number of diagnoses has risen in recent years, with approximately 200–300 new cases annually, partly due to the wider availability of MRI scans and increased awareness of the disease.
Causes
The precise cause of moyamoya disease remains uncertain. Pathologically, it involves a thickening of the innermost layer of the arteries (intima), leading to reduced blood flow. While there is debate over whether the condition is congenital or acquired, no clear answer has emerged.Infections are hypothesized to trigger an autoimmune response that may contribute to vascular inflammation, but this remains unproven. Genetic factors appear to play a significant role, as epidemiological studies indicate no strong environmental link. Studies in Japan have found no correlation with occupation, lifestyle, or geographic location.
Recent research has identified a genetic marker, the RNF213 gene, particularly the R4810K variant, which is prevalent among patients in Japan and Korea. This variant is present in 1–2% of the general population but is found in over 90% of familial moyamoya cases and 70% of sporadic cases. Interestingly, this variant is not found in Western populations, where other, rarer variants of the RNF213 gene, like N3962D and R4062Q, are associated with the disease. However, the exact function of the RNF213 protein is still unknown, making it difficult to state definitively that the R4810K variant is the cause, though there is a strong correlation.
The current understanding suggests that moyamoya disease arises when individuals with a genetic predisposition encounter certain environmental factors, leading to vascular narrowing.
Symptoms
The symptoms of moyamoya disease vary significantly depending on the patient’s age.Children
In children, the most common symptom is transient ischemic attack (TIA), or ‘mini-strokes,’ where blood flow to the brain is temporarily reduced. These often occur during times of emotional stress, such as crying or hyperventilating, and may result in temporary weakness in one limb. TIAs generally last only a few minutes and resolve on their own. Activities that require blowing, such as playing a wind instrument or eating hot food, can also trigger symptoms.Headaches are another common complaint in children, especially in the mornings. These may be accompanied by nausea and vomiting but typically improve with rest.
Adults
In adults, the first symptom is often a brain hemorrhage, occurring more frequently in individuals in their 30s and 40s. This can lead to severe headaches and loss of consciousness. Strokes or seizures are also possible initial symptoms. Adults may also experience intermittent headaches without other significant symptoms.Diagnosis and Tests
Suspicion of moyamoya disease based on symptoms is crucial for early diagnosis. Imaging techniques such as CT scans, MRI, MRA, and cerebral angiography are used to confirm the diagnosis.MRI and MRA (magnetic resonance angiography) are common tests that provide diagnostic information, while cerebral angiography offers a detailed view of the blood vessels. Other useful diagnostic tools include perfusion MRI to assess blood flow and Diamox-enhanced brain scans.
Treatment
Treatment decisions depend on the patient’s age, the severity of symptoms, and the progression of the disease.Children and Adolescents
Children with severe symptoms or rapidly progressing disease generally require immediate treatment. Surgery is often recommended, especially for younger children, to prevent further complications.Adults
In asymptomatic adults, doctors may opt for regular monitoring rather than immediate treatment. However, if there is significant blood flow reduction, preventive surgery might be recommended. When symptoms are present, treatment decisions are based on their severity and the progression of the disease.In the acute phase, ischemic symptoms are treated with medication to protect the brain and reduce symptoms, though no drug has been shown to cure moyamoya disease over the long term.
Surgical Options
Surgical intervention is considered when ischemic symptoms persist. The goal is to improve blood flow to the brain by creating a bypass between healthy vessels and the affected areas. The most common procedures include:Direct bypass surgery, often performed in adults, which connects the temporal artery to the middle cerebral artery.
Indirect bypass surgery, which involves procedures like encephaloduroarteriosynangiosis (EDAS), is more commonly used in children as it has fewer complications and better outcomes. Indirect surgery stimulates the formation of new blood vessels over time.
Since moyamoya disease typically affects both sides of the brain, a second surgery is often needed 2–4 months after the first. Surgery is delayed until after any initial stroke symptoms stabilize.
Post-surgical care focuses on preserving blood flow and preventing complications like new strokes. Most ischemic symptoms improve significantly following surgery, and cognitive decline or severe neurological deficits can often be prevented.
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