Most of us are aware of the common causes of stroke: A blockage in an artery in the brain can lead to an ischemic stroke, or a bleeding artery in the brain can cause a hemorrhagic stroke.

But there’s a less common cause of stroke known as moyamoya disease — a rare blood vessel disorder affecting the internal carotid artery in the skull that delivers blood to the brain. With moyamoya disease, this major artery becomes narrowed or blocked, reducing blood flow or cutting it off entirely. To compensate, tiny blood vessels develop at the base of the brain.

In Japanese, moyamoya means “puff of smoke” — a term used to describe the tangled appearance of these tiny vessels.

The condition may cause a ministroke, known as a transient ischemic attack, an ischemic stroke or a hemorrhagic stroke.

University of Michigan Health neurologist Garrett Conyers, M.D., M.P.P., and neurosurgeon David Altshuler, M.D., explain more about moyamoya disease and its treatment.

What is Moyamoya disease and how common is it?

Conyers: Moyamoya disease is a chronic, progressive disease characterized by narrowing of the bilateral internal carotid arteries inside of the skull. When you get narrowing of these internal carotid arteries, the brain adapts by developing an abnormal vascular network of tiny blood vessels that form at the base of the brain and provide new pathways for blood to flow. However, these vessels are fragile and do not always provide enough blood flow to support the functions of the brain.  

SEE ALSO: Ischemic vs. Hemorrhagic Stroke: What’s the Difference?

The disease, first diagnosed in Japan, is found in individuals throughout the world, although its incidence is higher in East Asian countries. It affects approximately 10 in one million individuals. We typically see moyamoya disease diagnosis peak in children around the age of 10 and in adults around 40. However, patients can develop moyamoya at any age.

What are the symptoms?

Conyers: Most patients come to us with symptoms associated with a transient ischemic attack or an ischemic stroke. These include facial asymmetry, weakness or sensation changes on one side of the body, and slurred speech.

Secondary symptoms may also develop as a result of a stroke caused by moyamoya disease, including headaches, seizures, involuntary movements, vision problems and cognitive or sensory impairment. These symptoms are typically caused by underlying damage to the structure of the brain due to a loss of blood flow.

Moyamoya is different [from other causes of stroke] in the sense that it's much more of a process of lack of blood flow to the brain due to regression of diseased vessels in the brain.”

 — David Altshuler, M.D.

How is moyamoya disease diagnosed?

Conyers: Typically, a patient comes to us after having an ischemic or hemorrhagic stroke impacting the deep structures of the brain. Patients tend to be younger than the average stroke patient and typically lack classic stroke risk factors. When we look at their blood vessels with advanced neuroimaging techniques, we find abnormal narrowing of specific arteries that are not explained by other disease processes. The first step in a moyamoya workup is ruling out other mimicking conditions such as atherosclerosis, autoimmune disorders, infectious disorders or tumors. The most important step for these patients is getting the right diagnosis.

Who’s at risk for moyamoya disease?

Conyers: Moyamoya is a complex, multifactorial disease that we still do not entirely understand as a scientific community. Approximately 5-10% of patients with moyamoya will have a first-degree relative with the same diagnosis – suggesting a genetic role. However, we do not have a clear understanding of what specific genes are at play, nor how environmental factors influence the disease state. The overwhelming majority of patients with moyamoya disease do not have risk factors or a way to predict their illness.

Given that moyamoya it is a chronic, progressive disorder, we emphasize to patients the importance of good overall blood vessel health: nutritious diet (Mediterranean), moderate exercise 4-5 times per week, and smoking cessation.

How is moyamoya treated?

Altshuler: Some patients with moyamoya disease who develop symptoms related to lack of blood flow to the brain may require surgical treatment. The goal of any surgery is to provide extra blood flow to the brain to prevent future strokes. For adult patients, there are two different types of surgery to provide blood flow. The first involves placing an artery near the brain so that blood vessels can grow into the brain over the course of months after surgery.

The second type of surgery is called a bypass and provides immediate new blood flow to the brain on the day of surgery. During a bypass procedure, the moyamoya blockages are bypassed by connecting a scalp artery to a brain artery to restore blood flow. For patients who qualify, this surgical intervention has the ability to definitely change the course of their illness and drastically reduce the rate of future strokes.

Both children and adults can benefit from surgery, but the exact type of treatment is a little bit different. Children typically respond better to what's known as an indirect bypass.

For adults, there's not a clear right answer whether indirect bypass or direct bypass is best. With direct bypass, we suture a donor artery to a recipient artery in the brain directly. In the acute setting where someone is having recent and rapidly progressive stroke-like symptoms, the rapid blood flow to the brain from a direct bypass is an advantage.

For children, indirect bypass is typically recommended because their ability to heal and grow new blood vessels is more robust than adults. This is why an indirect bypass tends to work quite nicely for pediatric patients in particular.

It really comes down to the correct operation for the correct patient along with an experienced team. Both direct and indirect bypass operations require special training above and beyond typical neurosurgical training, which makes it important to seek a team with extensive expertise in these types of surgeries. At U-M Health, we have a robust program that is recognized by physicians throughout the United States.

How does the type of stroke, caused by moyamoya disease, differ from other types?

Altshuler: The types of strokes patients with moyamoya disease experience don’t usually affect the large territory portions of the brain that are typically associated with most common forms of stroke, where a blood vessel gets acutely blocked. Moyamoya is different in the sense that it's much more of a process of lack of blood flow to the brain due to regression of diseased vessels in the brain. So, it's a blood flow-related issue rather than acute blockage from a blood clot or from plaque in an artery.

How important is it to seek immediate treatment for this kind of stroke?

Conyers: Like other stroke syndromes, early recognition and evaluation is of the utmost importance. If you have the classic FAST symptoms (Facial drooping, Arm weakness, Speech difficulties, Time to call emergency services) it is paramount that you call 911 and get evaluated immediately.