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Moya Moya Disease

What is Moya Moya Disease?

The term "Moya Moya" is of Japanese origin meaning "puff of smoke." This comes from the appearance of the brain blood vessels affected by Moya Moya syndrome during an angiogram (a special picture of the brain where an x-ray is taken after a special injection is given that allows your doctor to see the blood vessels). Moya Moya is a rare disorder of uncertain cause that leads to irreversible blockage of the main blood vessels to the brain as they enter into the skull.

Signs and Symptoms

In young children transient ischemic attack (mini-stroke) is the most common initial symptom. Some children may experience seizures or involuntary movements and even exhibit signs of mental retardation. In young patients, Moya Moya disease is usually associated with headaches, speech difficulties, and episodes of paralysis involving the feet, legs or upper extremities, hemorrhage and anemia.

In adults, presenting features are those of intracranial hemorrhage (bleeding within the skull). Disturbances of consciousness or subarachnoid hemorrhage is prominent. The arachnoid is a connective tissue sheath that covers the brain.

The patient may have fainting episodes (black outs). In addition, the patient may also suffer visual abnormalities may occur alone or in combination -- loss of sight in one eye (hemianopia), blurry vision (diplopia), poor vision in both eyes (bilaterally diminished visual acuity), and the inability to recognize objects. Papilledema, or localized swelling of the tissues affected may indicate subarachnoid or cerebral hemorrhage.

Epidemiology

The "Moya Moya" disease is often found among Japanese. The onset is the highest in the ages around 5 years and next in the 4th decade. The cause of the syndrome is unknown.

The process of narrowing of the brain arteries seems to be a reaction of the brain's blood vessels to a wide variety of external stimulus, injuries, or genetic defects. In a series of patients, the syndrome was associated with Asian birth (nine children), neurofibromatosis -- the congenital condition that causes tumors to grow on nerves (12 children), Down Syndrome (a chromosome defect -- 9 children), following cranial x-ray or chemotherapy treatments (10 children). There also seems to be an association with a previous history of surgery for congenital heart disease, suggesting that there may be a genetic defect in the blood vessel wall in these patients. But more than half of the children seen with this disease have no known cause for their Moya Moya syndrome.

The disease often progresses despite any known medical management unless treated with surgery. The repeated strokes can lead to severe problems with functions related to the area of the brain affected and may even cause death. It is important to recognize these lesions and treat them early on.

How is it diagnosed?

Once a diagnosis is suspected by CT or MRI, the next step is usually an angiogram to confirm the diagnosis and to see the what the blood vessels involved look like. Often nuclear medicine studies such as SPECT (single photon emission computerized tomography) are used to show the decreased blood and oxygen supply to areas of the brain affected with the Moya Moya disease.

How is it treated?

There is no cure for Moya Moya disease. Treatment is symptomatic and supportive. Certain medications can be very helpful in the treatment of the symptoms caused by Moya Moya syndrome. The basis for some of the strokes in this condition is sludging of blood within the narrowed arteries at the base of the brain, the formation of tiny blood clots at these areas, and the subsequent breaking off of these clots into downstream blood vessels -- which blocks them off temporarily or permanently.

Medicines which prevent this micro-clot formation, such as aspirin, are essential in Moya Moya syndrome, and some doctors believe that all Moya Moya patients need to be on the medication permanently as a preventive step.

Calcium channel blockers such as Verapamil are also often prescribed for patients with Moya Moya syndrome. These medications are often helpful in reducing the headache that certain patients may suffer during various stages of the illness, but they need to be given under the supervision of a neurologist. It is important to understand, however, that no medications prevent the arterial narrowing process from progressing or keep the Moya Moya vessels from developing, and surgery is the mainstay of treatment for the syndrome.

The neurosurgeon has to decide what type of operation is best suited for the child. There are many operations that have been developed for the condition. Surgical treatment has less success for an adult.

  • EDAS (encephaloduroarteriosynangiosis) procedure. This procedure requires freeing up, without severing, a scalp artery over a course of several inches and then making a small temporary opening in the skull directly beneath the artery. The artery is then sutured to the surface of the brain and the bone replaced.
     

  • EMS (encephalomyosynangiosis) operation. Here a muscle which on the temple and slightly on the forehead region of the skull, is freed from some attachments. A hole it then made in the skull under this muscle and it is then placed onto the surface of the brain.
     

  • STA-MCA (superficial temporal artery-middle cerebral artery) in which a scalp artery is directly sutured to a brain surface artery.
     

  • Multiple small holes (burr holes) are placed in the skull to allow for growth of new vessels into the    brain from the scalp.

All of these operations work on the concept of a blood and oxygen "starved" brain reaching out to grasp and develop new and more efficient means of bringing blood to the brain, this then bypasses the areas of blockage.

Are there risks involved with surgery?

The risks of the surgery seem to be more due to the risk of being under general anesthesia for an extended period of time then to the actual surgical manipulations.

The problem is the sensitivity of the affected vessels and the part of the brain affected. These areas are very sensitive to changes in blood pressure, volume and also the relative amount of carbon dioxide. All these things may vary dramatically under general anesthesia and surgery. When awake, the child's brain is able to regulate these factors fairly well.

However, under general anesthesia these parameters are much harder to artificially control and this can lead to bleeding or strokes. The anesthesiologist must have experience in managing these children as the type of anesthesia they require is very different from the standard anesthetic children get for almost any other type of brain surgery.

Outlook

The long term outlook for children with treated Moya Moya appears good. It will take probably 6-12 months before new vessels can develop after surgery and symptoms may seem to improve almost immediately after surgery. Unfortunately, once major strokes or seizures occur there may be permanent damage to the brain that cannot be corrected with surgery.

No one knows whether the form of Moya Moya syndrome prevalent in most children, which causes strokes and transient ischemic attacks (mini-stroke), will be replaced in adulthood by the bleeding form seen more commonly in adults. There is some evidence to suggests that this change in pattern is unlikely, since most adult patients don't have histories of stroke after surgery for Moya Moya when they were younger.

An Example of Moya Moya Disease

These angiograms are antero-posterior views of the right carotid artery injection. Contrary to the top normal angiogram (A), the angiogram of a Moya Moya patient shows marked development of the Moya Moya vessels at the base of the brain and marked narrowing of the terminal portion of the internal carotid artery. The middle cerebral and anterior cerebral arteries are poorly visualized (B).

(A)Normal Angiogram(B)Moya Moya Angiogram