Moyamoya Disease | Symptoms and Causes

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Contact the Moyamoya Disease Program

While Moyamoya disease is quite rare—only a few hundred children worldwide are diagnosed with the disease each year—it is a life-threatening condition that calls for immediate attention by an experienced neurosurgical team. 

Here in Boston Children’s Hospital’s Moyamoya Disease Program, we treat patients of various ages; while the average age at which a child is diagnosed with Moyamoya is 7, children of all ages can develop the disease, as can adults. Some children with Moyamoya have other medical conditions, like Down syndrome, sickle cell disease and neurofibromatosis, and our clinicians work closely with specialists throughout the hospital to deliver comprehensive, multidisciplinary care. 

Moyamoya disease: The basics

  • The disease process begins when the internal carotid arteries—the major vessels that provide nourishing blood to important areas of the child's brain—become thickened and narrowed. 
  • When the carotid arteries are compromised, blood flow becomes dangerously slowed and clots may form—significantly increasing the chances of a transient ischemic attack (TIA), also known as a “mini-stroke,” or a full-fledged stroke. 
  • The child's brain attempts to compensate for the reduction in blood flow by gradually generating “detours”—the growth of thin, small blood vessels throughout the affected areas. 
  • These vessels look like a tangled wisp of smoke on an angiogram—a map of the arteries or veins in a certain area of the body—giving the disease its name: “Moyamoya” translates to “puff of smoke” in Japanese. 
  • Because Moyamoya disease becomes progressively more severe over time, children with the condition will eventually need surgery to restore normal and healthy blood flow to their brains and reduce the likelihood of a stroke. 
  • Pial synangiosis, a surgical procedure developed by Boston Children's neurosurgeon R. Michael Scott, MD, more than 25 years ago, has proven to be highly effective treatment for Moyamoya disease. Children’s research has shown that, in all patients treated with pial synangiosis here in our Moyamoya Disease Program, the incidence of strokes has dropped from more than 67 percent to less than 7 percent.

Causes of Moyamoya Disease

What causes Moyamoya disease in children?
Because Moyamoya disease is so rare, and information about the progression the disease is limited, its causes are still not fully understood. Experts believe that a variety of factors—ranging from genetic defects to traumatic injury—may trigger the narrowing process in the brain's carotid arteries. However, investigation to pinpoint an exact cause is still ongoing, and in at least half of all known cases of Moyamoya, the disease have no identifiable cause.

Gender and ethnicity factors
Moyamoya disease is slightly more common in girls than in boys, and somewhat more common in children of Asian descent than in other ethnic backgrounds.

Genetic factors
About 7 percent of children with Moyamoya disease are believed to have an inherited gene defect. 

Associated disorders
Some children with Moyamoya disease also have another condition, such as:

This suggests that an inherited, defective blood vessel structure may be linked to Moyamoya.

Stay up to date on Boston Children’s continuing research into the causes of Moyamoya disease.

Signs and symptoms of Moyamoya Disease

What are the symptoms of Moyamoya disease?
Children with Moyamoya disease usually show symptoms consistent with a stroke, such as:

  • weakness on one side of the body
  • blurry or otherwise affected vision
  • slurred speech
  • headaches
  • seizures, especially when they occur in a child with no prior history of a seizure disorder

These symptoms can either emerge gradually and subside over time, or develop suddenly and persist. 

Rarely, a child with Moyamoya may have a brain hemorrhage—bleeding in the brain—but hemorrhaging is much more likely to occur in adults with Moyamoya disease. Warning signs of a brain hemorrhage can include:

  • nausea
  • vomiting
  • fatigue and lethargy
  • changes in vision
  • severe headache
  • numbness in part of the body

You should seek immediate medical treatment if your child exhibits any of the above warning signs.

Frequently Asked Questions about Moyamoya Disease

Q: At what age do Moyamoya symptoms typically emerge?
Though 7 years is the average age of diagnosis, Moyamoya disease can affect people of any age. 

Q: Are there different types of Moyamoya disease?
A: Yes. The childhood form of the disease causes stroke symptoms, such as slurred speech, headaches and seizures

Young adults and older people with Moyamoya may also have the hemorrhagic form of the disease, in which a brain hemorrhage—bleeding in the brain—is a symptom. 

Here at Boston Children’s Hospital, we’ve compiled data suggesting that it’s very rare for someone with childhood Moyamoya disease to develop the hemorrhagic form later in life. 

Q: Will my child be OK?
The long-term outlook for a child with Moyamoya disease depends very much on his individual circumstances, including:

  • his symptoms at the time he is diagnosed
  • whether one or both sides of his brain are affected
  • whether he has already suffered a transient ischemic attack (TIA) or stroke
  • his overall health
  • how soon he receives surgical treatment after diagnosis 

Your child’s treatment team can give you detailed information on his particular situation, and can recommend the best course of action. 

Q: Is it possible that my child’s Moyamoya disease will go away on its own?
No. It’s important for families to understand that Moyamoya disease is a progressive condition: the dangerous narrowing in the brain’s blood vessels continue to worsen. Some children’s symptoms become gradually more severe over months, or even years, but others suffer multiple transient ischemic attacks (TIAs) or strokes in a relatively short period of time. Surgery to provide a new, healthy source of blood flow to the brain is a must to reduce the likelihood of a potentially life-threatening stroke. 

The good news is that the children and adults we have treated surgically have had an excellent rate of recovery. Learn more about how Boston Children’s treats Moyamoya

Q: What do I need to look out for once my child has been diagnosed with Moyamoya disease?
Parents of children with Moyamoya disease should be watchful of any symptoms that suggest a possible stroke. These include:

  • blurry or otherwise abnormal vision
  • weakness or paralysis on one side of the body
  • loss of sense of smell or taste (often in just one side of the nose or mouth)
  • difficulty speaking or inability to speak
  • inability to stand upright
  • inability to walk
  • seizures, especially if the child has no prior history of seizure activity

Though the hemorrhagic form of Moyamoya disease is much more common in adults than in children, you should also keep an eye out for possible warning signs of a brain hemorrhage (bleeding in the brain) in your child. Symptoms can include:

  • severe headache
  • sudden loss of consciousness
  • loss of coordination or balance
  • fatigue or lethargy
  • nausea or vomiting
  • changes in vision
  • weakness, tingling or numbness, especially in an arm or leg
  • difficulty understanding speech
  • difficulty speaking
  • complaints of a “strange” taste in the mouth
  • seizures, especially if the child has no prior history of seizure activity

You should always seek immediate medical help if your child experiences any of these symptoms.

Q: Should my child’s physical activity be restricted?
Symptoms of Moyamoya disease are often brought on, or made worse, by activities that can lead to hyperventilation (over-breathing), a drop in blood pressure or dehydration—all risk factors for a stroke.

To lessen the risk of stroke, activities should be restricted—especially strenuous play or sports than can cause overexertion. Your clinician can make more detailed recommendations for your child.

Q: Can adults develop Moyamoya disease? How is the condition different than in kids?
Though the average age of a person with Moyamoya disease when they are first diagnosed is 7, the disease can also develop in older children, adolescents and adults.

Adults may have the hemorrhagic form of Moyamoya. Based on the evidence we have collected here at Boston Children’s, it appears very unlikely that a child with Moyamoya disease will develop the hemorrhagic form later in life.

Our Moyamoya Disease Program treats adults as well as children. Contact us to request an appointment, second opinion or consultation. 

Q: How long has Boston Children's been treating Moyamoya disease?
In 1985, Boston Children’s neurosurgeon R. Michael Scott, MD, performed the first pial synangiosis procedure—which he developed—for a child with Moyamoya disease. Since that time, he and colleague Edward Smith, MD, director of Pediatric Cerebrovascular Surgery at Boston Children’s, have treated more than 400 patients with the condition. Pial synangiosis surgery remains the mainstay of treatment for Moyamoya disease at Boston Children’s. 

Q: Why is surgery the recommended treatment for Moyamoya disease?
Moyamoya disease is a progressive condition: The degree of narrowing in the brain’s blood vessels only grows more pronounced over time, as will the associated symptoms and the risk of a potentially fatal stroke.

To combat this dangerous process, a new source of nourishing blood vessels must be found. Surgery is necessary to introduce new vessels and restore healthy blood flow to the brain. 

Q: Why does Boston Children’s recommend the pial synangiosis procedure, in particular?
Since the pial synangiosis procedure was first developed at Boston Children’s more than 25 years ago, we have used the operation to successfully treat more than 400 children and adults with Moyamoya disease. 

Pial synangiosis is particularly effective because it:

  • uses a wide opening of all of the membranes covering the brain
  • directly attaches the donor artery to the brain surface, promoting more rapid development of arterial ingrowth to nourish the child’s brain
  • takes advantage of the tendency of the brains of children with Moyamoya disease to attract new blood vessels from any source that is made available by the surgeon

Most children who have pial synangiosis are released from the hospital within a few days, and usually need only regular exams and monitoring as follow-up. 

Q: How likely is it that my child will suffer a stroke during surgery?
A: Based on more than 400 patients with Moyamoya disease who have undergone pial synangiosis surgery at Boston Children’s, it’s estimated that four to seven percent will suffer a new stroke either at the time of surgery or within the first month after the operation. These strokes can range from mild transient ischemic attacks (TIAs) (“mini-strokes”) to more severe episodes.

It’s important to note that most of the Children’s patients who suffered strokes during or after the procedure were already experiencing serious neurological symptoms—including frequent TIAs or strokes—in the weeks or months leading up to their surgery. We believe that patients with this type of history are at greater risk, and as a result, we will typically wait four to six weeks after any stroke episode before proceeding with surgery.

Nearly all of the Boston Children’s patients who suffered a stroke at the time of, or just after, surgery have gone on to make excellent recoveries. 

Q: Is the rest of my family at risk for Moyamoya disease? Should my child’s siblings be screened?
A:  Inherited Moyamoya disease appears to be quite rare in the Western hemisphere. If your family doesn’t have a history of strokes, we don’t usually recommend screening siblings of children with Moyamoya disease for the condition. (However, if one of your children is experiencing either warning signs of a stroke—like severe headaches or seizures—or an actual TIA or stroke, you should seek immediate medical treatment, including screening for Moyamoya.)

We do recommend screening in these cases:

  • identical twins of children with Moyamoya disease
  • siblings of children with Moyamoya disease, in families with a history of early stroke

Q: Does Boston Children’s recommend/offer genetic testing for Moyamoya disease?
There is no current method of determining before birth whether a baby is likely to have Moyamoya disease.

Even if a reliable prenatal test for Moyamoya existed, no one knows exactly when the process of blood vessel narrowing begins in the brain. It’s possible that any test administered during pregnancy or in the first year of the baby’s life would not be able to detect the potential presence of Moyamoya disease.

Q: Can my child go on to live a normal adult life, including having a family?
A: While the rarity of Moyamoya disease—and the relative newness of surgical advances like pial synangiosis—means data on long-term outcomes is somewhat limited, the results we have seen here at Children’s are very encouraging.

In our Moyamoya Disease Program, we continue to track the progress of all of our patients, dating back to the first pial synangiosis procedure in 1985. The vast majority of the 400-plus patients treated for Moyamoya disease at Boston Children’s have done exceedingly well: More than two-thirds are leading normal, active adult lives today, with no noticeable neurological problems.

In addition, several of the children we treated in the 1980s and 1990s now have families of their own. This includes many women who have experienced uncomplicated pregnancies and deliveries.

Questions to ask your doctor about Moyamoya Disease

You and your family play an essential role in your child’s treatment for Moyamoya disease. It’s important that you share your observations and ideas with your child’s treating physician, and that you have all the information you need to fully understand the treatment team’s explanations and recommendations.

You’ve probably thought of many questions to ask about your child’s symptoms and prognosis. It’s often very helpful to jot down your thoughts and questions ahead of time and bring them with you, along with a notebook, to your child’s appointment. That way, you will have all of your questions in front of you when you meet with your child’s treating clinician and can make notes to take home with you. (If your child is old enough, you can encourage him or her to write down questions, too.)
Initial questions to ask your doctor might include: 

  • How did you arrive at this diagnosis?
  • Are there any other conditions my child might have instead?
  • Does my child require further testing or procedures?
  • How extensive is the blood vessel narrowing in my child’s brain? Are both sides of the brain affected?
  • Should my other children be screened for Moyamoya?
  • What medications will you prescribe and what are the possible side effects?
  • Should my child's physical activities be restricted?
  • Will my child need surgery immediately?
  • Do you recommend pial synangiosis or another procedure, and why?
  • What role should I play in my child’s treatment?
  • How should I talk to my child about Moyamoya disease and the long-term outlook?
  • How should I explain my child’s condition to others?
  • Do I need to make any other changes to my child’s home and school routines?
  • What other resources can you point me to for more information?

Helpful links

Please note that neither Boston Children’s Hospital nor the Moyamoya Disease Program at Boston Children’s unreservedly endorses all of the information found at the sites listed below. These links are provided as a resource.

Information about associated conditions

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