Contents of This Section:

1. What is moyamoya disease?

Moyamoya disease (note the correct spelling is moyamoya, not moya moya) is a condition where there is progressive blockage or occlusion of the ends of the internal carotid arteries and their major "terminal" branches in the brain. In jargon, "a progressive obliterative arteriopathy affecting the intracranial circulation". The condition affects the anterior circulation, and tends to spare the posterior circulation ( take me to Brain Arteries now). The arterial blockage leads to a classic "puff of smoke" appearance on a cerebral angiogram (Figure 1). The "puff of smoke" is actually a myriad of tiny vessels that forms in response to the blockage, in order to allow blood to continue flowing to the brain through this alternate tiny vessel network or pathway. The word moya is Japanese, and is taken to mean "tiny", referring to the tiny vessel network that forms. Moyamoya disease affects children and also adults.

Moyamoya Disease:

2. Why does moyamoya disease occur?

The precise cause of moyamoya disease is unknown. There are several disease states that are associated with moyamoya disease. These include: neurocutaneous syndromes such as Sturge-Weber syndrome and neurofibromatosis, meningitis, Down syndrome, fibromuscular dysplasia, childhood brain radiation, Fanconi's anemia, and brain atherosclerosis. Inheritance (family history) may play a role in some patients in moyamoya disease. Vasculitis, or inflammation of the blood vessel wall, which can occur in a variety of medical conditions, may also lead to the development of moyamoya disease.

3. What are the symptoms and signs of moyamoya disease?

In children, moyamoya disease typically presents with symptoms and signs of a transient ischemic attack (TIA) or completed stroke ( take me to the section on Brain Attack now). It can also present with seizures. In adults, moyamoya disease usually presents with symptoms and signs of a brain hemorrhage, but can also present as a TIA or ischemic stroke. The hemorrhage may manifest as sudden severe headache, neurological impairment (as in a stroke), or collapse. The hemorrhage may be deep in the brain, referred to as intraparenchymal hemorrhage (IPH), or may be a subarachnoid hemorrhage (SAH). Hemorrhage occurs because of weak moyamoya vessels, or because of true brain aneurysms associated with moyamoya disease ( take me to the section on Brain Aneurysms now).

4. What are the complications of moyamoya disease?

Ischemic stroke, brain hemorrhage, seizures and death are the major complications of moyamoya disease. In persons with moyamoya disease, the death rate (usually from brain hemorrhage) is somewhere between 5-10%.

5. How is moyamoya disease investigated?

A regular CT head scan and MRI head scan (with diffusion weighted imaging or DWI sequence) can show strokes and hemorrhages associated with moyamoya disease. A CT-angiogram or MR-angiogram may show the abnormal vessels (blockages and microvessel proliferation) and any aneurysms associated with this condition. However, the gold-standard for evaluation of moyamoya disease is cerebral angiography. Here, a contrast dye is first injected through a catheter device inserted usually in a thigh (femoral) artery. From here, the dye eventually enters one or more of the main brain arteries, where it is X-ray imaged. The classic appearance of moyamoya disease on a cerebral angiogram is depicted in Figure 1. An angiogram may also show brain aneurysms and, rarely, brain arteriovenous malformations (AVM) which can both occur in patients with moyamoya disease ( take me to the section on Brain Aneurysm or AVM now). The brain aneurysms can occur anywhere in the brain circulation in moyamoya patients.

Special investigations for moyamoya disease include CT-perfusion and positron-emission-tomography (PET) scanning. These techniques can characterize the amount of brain ischemia or circulation impairment and "circulatory reserve" as part of an evaluation of the moyamoya patient for possible brain bypass (see below). Finally, some patients with moyamoya disease have abnormal blood test markers (e.g., anti-double stranded DNA antibodies), the precise significance of which is unkown.

6. How is moyamoya disease treated?

Medical managment of moyamoya disease has unproven benefits. That is, benefit from the use of steroids, aspirin or equivalent blood thinners, vasodilators, etc., is not established in this condition. On the other hand, surgery is regarded as the major treatment option for moyamoya disease patients suffering from progressive neurological symptoms from brain ischemia, or who suffer the effects of brain hemorrhage. In patients with moyamoya disease, surgery may involve evacuation of a brain hematoma, clipping of a ruptured brain aneurysm, or brain bypass ( take me to the section on Brain Bypass now).

Brain bypass in the setting of moyamoya disease takes two major forms:

1. A direct bypass procedure, namely, superficial temporal artery (STA) to middle cerebral artery (MCA) bypass. This is referred to as a "STAMCA bypass".
2. An indirect bypass or "onlay" procedure such as encephaloduromyosynangiosis (EDMS), with or without a direct bypass aswell.

7. Link to a patient-oriented moyamoya disease Website.

For further information regarding moyamoya disease, including a variety of helpful links, visit www.moyamoya.com, a comprehensive patient-support Website.