Understanding Moyamoya Disease in Children

When Malachi Horton was 18 months old, he lost movement in his right arm and leg and was unable to sit, stand or walk. “We took him to three different emergency rooms before he was diagnosed as having a stroke,” his mother Erin Horton said.

Dr. Ed Smith

There are many causes of stroke, but one of the most unusual is moyamoya disease, a blood vessel or vascular disease in which an ischemic stroke or TIA may be the first symptom. Although adults can have it, it is more common in children (age 2-5, although any age is possible). We talked about this disease with Ed Smith, M.D., a pediatric neurosurgeon, co-director of the Neurosurgical Stroke Program at Boston Children’s Hospital and an expert on moyamoya and other vascular diseases of the brain.


Moyamoya causes the two large blood vessels that pass through the front of the neck to the brain — the internal carotid arteries — to narrow over time. This reduces the blood supply to the brain, which raises the risk of a TIA or ischemic stroke.

The disease is different from other artery-clogging diseases like atherosclerosis. “It’s caused by an overgrowth of muscle within the artery that narrows it from the outside in as opposed to plaque clogging it from the inside,” Dr. Smith said.

Another way that moyamoya differs from other types of diseases is that when the brain gets starved for oxygen, it calls for help by either widening tiny existing blood vessels or growing new ones to get additional blood flow in the brain. “It is similar to traffic problems, kind of like when a major six-lane highway is shut down to just one lane, so all the tiny back roads become swollen with traffic and people look for new routes to get where they need to go,” Dr. Smith said. Both the old and new blood vessels get engorged trying to bring extra blood to the brain. Named by a Japanese doctor who described the condition in the 1960s, moyamoya is Japanese for “puff of smoke” because that’s how the engorged vessels appear in X-rays of the head.

The problem is that new and existing blood vessels can’t possibly carry the same amount of blood if the parent arteries (the carotids) shut down, starving the brain of oxygen.

Unlike atherosclerosis, which can be stabilized or reversed, moyamoya is always progressive — the carotid arteries continue to narrow. If left untreated, ultimately moyamoya will lead to strokes and death. Its progression varies, although in children it can progress quickly.


Pc0100200According to Dr. Smith there are likely several different conditions that look the same on X-ray, act the same in terms of causing symptoms but are caused by different underlying medical problems. For example, there are number of different genes that seem to be related to Asian populations that get moyamoya but are not present in Caucasian or North American populations. On the other hand, there are American populations that have a mutation that causes a moyamoya-like condition that is not related to the Asian version. “Among our patients, we have several identical twins, so they have the same genes but one has moyamoya and the other doesn’t,” said Dr. Smith. “So, clearly, number one, there are several different types of causes for moyamoya. And number two, there’s both an environmental influence and a genetic influence.”

In addition, moyamoya is often not recognized as a cause of stroke in some children with sickle-cell disease because their condition mimics moyamoya. “I think there are close to 400,000 people in the U.S. with sickle-cell disease and up to 10 percent of those will have a stroke before they’re age 20,” Dr. Smith said. “Of those, about 40 percent will have some sort of abnormality in the MRI that would look like moyamoya.”

Initial studies suggested that about one in a million people have moyamoya, which extrapolates to roughly 310 cases a year in the U.S. Given the number of cases he sees each year, Dr. Smith thinks that is a gross under-estimation, especially if the percentage of children with sickle-cell is added.


There are no effective drug treatments for this condition, so essentially, the solution is to build a new plumbing system. “The brain doesn’t care where the blood comes from, whether it’s from the carotid or some other place, as long as it’s getting blood with oxygen,” said Dr. Smith.

With moyamoya, it is impossible to reconstruct the internal carotids coming through the neck. Attempts to do angioplasty to stretch them open have failed because unlike atherosclerosis, moyamoya is a disease that covers the length of the artery, not just one spot.

There are two types of surgery — direct and indirect. Both use the same source of blood to build a new supply — branches of the external carotid artery in the scalp, which are typically not affected by moyamoya.

In the direct technique, a blood vessel in the scalp is cut in half and one half is sewn directly into an artery in the brain that supplies blood to the brain’s cortex. This supplies blood immediately, but it is harder to do on children because their blood vessels are so small.

The indirect technique uses the same scalp blood vessels, along with other blood vessels in the lining of the brain (the dura or meninges). These vessels are surgically implanted under the skull, and allow an entirely new system of blood vessels to grow — a process called angiogenesis. These new vessels take several weeks to months to grow. Indirect surgery is more commonly used in children; the direct technique is more common in adults.

The really good news with this procedure is that once done, there is almost never a need to do it again. Though their stroke deficits are not reversed, many children are able to lead normal lives.

Haleigh’s Story

Haleigh Martin

At the end of June 2012, Michelle Martin of New Orleans noticed her six-year-old daughter Haleigh experiencing involuntary body movements while attending a friend’s birthday party. Ten days later, Haleigh was diagnosed with an involuntary movement disorder called chorea and sent to Children’s Hospital of New Orleans to see what was causing it. After testing, she was diagnosed with moyamoya. “We were also told that she had already had four strokes, and the chorea was a result of those,” Michelle said.

Haleigh was given an “Arnold Schwarzenegger-dose of steroids for the chorea” and daily aspirin to help prevent future strokes. The Martins were told the only treatment for moyamoya was surgery, and her records were sent to Boston Children’s where she had indirect surgery on September 4, 2012. During the time between diagnosis and surgery, Haleigh had a fifth stroke.

As a result of her strokes, when Haleigh gets excited or experiences anxiety, the chorea movements return. She also has subtle learning and speech issues, which are noticeable to her family. She cannot take any medicine that can cause the blood vessels to constrict, like decongestants or antihistamines. “It can be hard watching her not getting any relief and having to let some things run their course,” her mother said. “Also, because she is restricted from contact sports and activities, as well as anything that can cause her to become overexerted, our biggest challenge is finding the balance between protecting her and allowing her to be a normal seven year old.”

After Haleigh was diagnosed, Michelle replayed earlier events and realized she was there when Haleigh had two strokes. “I was devastated and beat myself up that I didn’t recognize the signs,” she said. “Immediately after the surgery, it was like having a newborn again because my husband and I found ourselves checking to make sure she was breathing. Now, we try not to focus on what she can’t do, but on finding those things that she can do.

Malachi’s Story


Malachi Horton

When Malachi Horton was 18 months old, he lost movement in his right arm and leg and was unable to sit, stand or walk. “We took him to three different emergency rooms before he was diagnosed as having a stroke,” his mother Erin Horton said.

At first doctors thought he had a clotting disorder, but a cerebral angiogram detected moyamoya disease. It also showed a number of possible TIAs. The Horton’s family doctor explained that Malachi would need brain surgery as soon as possible. “Without it, the strokes would continue until they took his life,” Erin said. To reduce the risk of another stroke, he was kept cool and well hydrated and given low-dose aspirin.

He had the indirect-type of surgery at Boston Children’s Hospital on June 29, 2010, and his prognosis is good. However, his stroke was not without consequences: his right side is weaker than his left, and he has limited fine motor skills in his right hand. “We also see him get angry or agitated quickly,” Erin said. “I have been told this is common in people with a history of strokes.”

Because of moyamoya, the Hortons are much more proactive about Malachi’s medical care. “We take time to ask questions and do our own research,” Erin said. “We are more vocal about our concerns and voice them when we feel they are not being addressed. Malachi’s ultimate diagnosis of moyamoya would not have changed, but perhaps the severity of his stroke would have changed if our concerns had been taken seriously at the first sign.”





Claire’s Story

Claire Sargent

Between August and November 2012, nine-year-old Claire Sargent had a series of excruciating headaches. Her doctor ordered an MRI, which showed abnormalities that proved to be three hemorrhagic strokes. She was referred to a neurologist near her hometown of Grand Rapids, Mich. A follow-up MRI showed she had moyamoya disease, and Claire was referred to a neurosurgeon. She had indirect-type surgery in December, four months after her first headache.

“Claire is not progressing at the average rate for this kind of indirect bypass,” said her mother, Andrea Sargent. “Her prognosis is still unknown.” Her blood flow at her six month checkup was mostly unchanged. “She is still at extremely high risk of additional strokes and TIAs, but our hope is that each day her risk lessens.”

Claire was an honor roll student before her strokes, diagnosis and surgery, plus a TIA in April 2013. Today, “she has some cognitive deficits in the areas of working memory, sustained auditory attention and visual organization, with a cognitive impairment in the area of executive functioning,” her mother said. Her education going forward will be guided by a lengthy Individual Educational Plan. She started 5th grade in September.

Andrea doesn’t know if Claire’s deficits are due to the strokes or surgery. She tires more quickly and her thought patterns are different. “She is forever altered by what she’s been through,” Andrea said, “but remains a mostly happy-go-lucky pre-teen, although she struggles mightily now that things take longer and are harder to do. It causes tremendous frustration and anxiety, which is why she was recently diagnosed as having an adjustment disorder with anxiety.”

Claire can’t do a lot of activities that she used to because she’s still at an extremely high risk of stroke. Dehydration, over-stimulation and fatigue can increase her chances of having another stroke. Her doctor says her body is expending a lot of energy simply healing from the trauma of surgery.

When Claire gets tired, her balance also suffers. She has taken more than a few tumbles down the stairs after an overactive day. “For now, Claire can’t be her normal, overactive, bouncy, busy little self,” her mother said. “She needs to take things a little easier, something she’s not fond of doing.”


Arianna’s Story

Arianna Carter

In the summer of 2003, five-year-old Arianna Carter of Herrin, Ill. began having symptoms that no one could explain. “She was playing with her sister and her left side seemed to go numb on her,” said mother Tammy Carter. Fortunately she was okay within a few minutes, and Tammy chalked it up to rough-housing. That fall Arianna began school, and her teachers noticed she was having similar episodes and needed a nap afterwards.

Her parents took Arianna to a specialist who thought she had DeJorges Syndrome because of learning disabilities that seemed consistent with it. Tammy began researching to see what could be done to help Arianna.

The numbness episodes persisted. During one, Arianna’s face drooped. Alarmed, Tammy took her to her pediatrician, who recommended a neurologist. “When I explained her symptoms as stroke-like, the neurologist laughed and said ‘Kids don’t have strokes, Mrs. Carter. You must be over-exaggerating a seizure.’”

However, Arianna’s neurologist said if she continued to have episodes, to take her to the nearest ER and tell them her doctor wanted an MRI. “Soon we were in the local ER,” her mother recalled. “When I told them what the doctor wanted, I was told they weren’t going to do it — too expensive. They said children do things for attention. Or it could be an ear infection. And again, we were told that children don’t have strokes, but seizures are common.”

The family was dealing the best they could. Tammy watched her daughter’s every move. After another incident of strange behavior, Tammy took Arianna to the ER in another town. She was in the middle of a numbness episode when they arrived. They did a CT scan, and the physician said it looked okay to him, although there was a blur on it, probably because she moved. “He wasn’t sure what was going on with her but did tell us to get to her neurologist as soon as we could and to come back if she had more episodes,” Tammy said.

The neurologist called the next morning, after receiving Arianna’s CT scan. “I will never forget what she said,” Tammy recalled. “‘Arianna is a very sick little girl. Take her to your local ER. There an ambulance will pick her up and take her to St. Louis Children’s Hospital. You have to go NOW!’” When Tammy asked why she couldn’t just drive her to St. Louis, two hours away, the doctor said that she might not survive the drive. “My heart dropped. I quickly made arrangements for my other daughter and called my husband. We were at the ER within 30 minutes.”

The doctor in St. Louis explained that the blur on the CT scan was a brain anomaly. Tammy was asked to explain the events of the previous months. “I was relieved to see someone taking me seriously,” Tammy said. Arianna was admitted for testing.

The test results showed Arianna had moyamoya disease. In January 2004 the Carters went to Boston for surgery, the direct technique. Further tests showed she’d had a major frontal lobe stroke and that the right side of her brain was 98 percent blocked and the left side 16 percent blocked. After surgery, Arianna had another massive stroke, which led to brain death. Her parents took her off life support on January 15, 2004.

After Arianna’s death Tammy was told she couldn’t hold the doctors in their small town responsible because “they just can’t be expected to know about these rare diseases. I find that unacceptable,” Tammy said. “So I try to educate as many as I can so that they do know. I don’t want another parent to be told, ‘Children don’t have strokes’ or ‘She’s just trying to get attention.’ I want to share her story to open eyes, not to dampen the hopes of anyone who has moyamoya. I want to help them prevent her story from being repeated.”


The adult version of moyamoya disease typically starts affecting people in their mid-40s and progresses more slowly than in children.

In children and adults, twice as many females have moyamoya compared to males.

Ischemic stroke is the most common outcome for adults and children with moyamoya, but adults sometimes have bleeding strokes because of higher blood pressure.

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