Moyamoya syndrome is a progressive disorder that affects the blood vessels in the brain. Approximately 10% of cases of Moyamoya syndrome are idiopathic and are termed primary Moyamoya syndrome or Moyamoya disease. Secondary Moyamoya syndrome refers to cases in which the syndrome is a consequence or result of another underlying disorder.

Moyamoya disease, taken from the Japanese meaning "a puff of smoke", is an idiopathic, progressive, intracranial vasculopathy leading to occlusion of the internal carotid arteries and their major branches, typically at their supraclinoid location. There is characteristic development of prominent basal, leptomeningeal and transdural collaterals. The posterior circulation is variably involved.

Etiology :

In many cases is indeed idiopathic; however, it is associated with NF1, radiation vasculitis, sickle cell disease and Downs syndrome. A familial form has been described. Moyamoya disease is most common in Asian populations.

Clinical Presentation :

The childhood form of moyamoya differs from adult in that children are more likely to suffer from ischemic infarction, perhaps repeated episodes, whereas adults are more likely to have hemorrhagic complications.

Children may have hemiparesis, monoparesis, sensory impairment, involuntary movements, headaches, dizziness, or seizures. Mental retardation or persistent neurologic deficits may be present.

Also in the childhood presentation of the disease, basal collaterals tend to be particularly prominent and the disease is quite often bilateral.

Pathophysiology:

The terminal ICA and proximal anterior and middle cerebral arteries are severely narrowed or occluded by an extensive fibrocellular intimal thickening. Characteristic collaterals form with supraclinoid obstruction of the internal carotid arteries There are three basic collateral pathways: basal moyamoya vessels from perforators(the lenticulostriate, thalamoperforate and thalamogeniculate vessels),leptomeningeal collateral vessels from the posterior cerebral artery, and transdural collateral vessels from the external carotid artery (meningeal, superficial temporal and occipital arteries) . The basal moyamoya collaterals themselves have unique pathological characteristics. Some are thin-walled and dilated, while others are thick-walled and stenotic. Those basal collaterals that are thin and dilated are often associated with significant vessel fibrosis and marked attenuation of the media, changes that may predispose moyamoya patients to microaneurysm formation. The presence of microaneurysms, increased hemodynamic stress, and vessel wall necrosis are all considered likely etiologies for the cerebral hemorrhages that often occur in adult-onset moyamoya disease. Common locations for such hemorrhages include the basal ganglia, thalamus, and ventricular system, all of which have great proximity to these fragile basal collateral vessels.

Imaging:

Angiography: Cerebral angiography is the principal imaging study utilized for the diagnosis of moyamoya disease.

There are several forms of grading moyamoya which are based on the angiographic characteristics. One has been proposed by Suzuki and Takaku, the other proposed by Satoh. The former is a six-stage system; the latter is five-stage. Basically, the stage is dependent upon the formation, development and reduction of typical collaterals.

Angiographic ICA staging of stenoocclusive lesions in patients with moyamoya disease

Stage I : Narrowing of the carotid bifurcation.

Stage II : Dilatation of the ACA and MCA with appearance of ICA moymoya.

Stage III : Partial disappearance of the ACA and MCA with intensification of ICA moyamoya.

Stage IV : Advanced stenoocclusive changes in the ICA ( ACA and MCA are traced very dimly or in a completely different shape with small amount of ICA moyamoya.

Stage V : Absence of the ACA and MCA with further reduction of ICA moyamoya.

Stage VI : Blood supply only from the external carotid artery with almost complete disappearance if ICA moyamoya. Vault moyamoya vessels can also be seen, with dural and pial collaterals developing secondary to reduced blood flow.

MRI:
With high diagnostic accuracy, magnetic resonance (MR) imaging and MR angiography are very useful in assessing moyamoya disease in children. It has been observed that contrast material–enhanced MRimages in patients with moyamoya disease show marked leptomeningeal enhancement and that there is a reduction in enhancement after bypass surgery. Some authors call this leptomeningeal enhancement the "ivy sign," which is considered to represent the fine vascular network over the pial surface. This sign is best depicted on contrast enhances T1 weighted and FLAIR images.

Diagnosis:
Strict guidelines for the diagnosis of moyamoya disease have been established by the Research Committee on Moyamoya Disease of the Ministry of Health and Welfare in Japan. Definite diagnosis of moyamoya disease requires the following:

1.Bilateral steno-occlusive changes in the terminal internal carotid artery (ICA) and/or proximal portions of the anterior or middle cerebral arteries,

2. Abnormal vascular networks in the vicinity of the steno-occlusive disease, and

3. No accompanying systemic disorders.

Probable diagnosis of moyamoya disease is established if the steno-occlusive disease and associated abnormal vascular network are noted unilaterally, with progression to definite moyamoya disease (i.e., bilateral lesions) seen in 7 to 50% of patients.

Finally, the term quasi-moyamoya disease or moyamoya syndrome is typically used to refer to patients who display steno-occlusive lesions and associated collaterals in other areas of the brain or who have systemic disorders that account for the observed vasculopathy (e.g., arteriosclerosis, autoimmune disease, Down syndrome, von Recklinghausen's disease, previous head irradiation, or meningitis).

Treatment :

Surgical revascularization :

Direct :

STA-MCA Bypass: In the STA-MCA procedure, the scalp artery (superficial temporal artery or STA) is directly sutured to an artery on the surface of the brain (middle cerebral artery or MCA). This procedure is also commonly referred to as an EC-IC (External Carotid-Internal Carotid) bypass.

The EDAS (encephaloduroarteriosynangiosis) procedure requires dissection of 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.

In the EMS (encephalomyosynangiosis) procedure, the temporalis muscle, which is in the temple region of the forehead, is dissected and through an opening in the skull placed onto the surface of the brain.

Encephaloduroarteriomyosynangiosis (EDAMS). This combines EDAS with EMS.

Other techniques such as the placement of multiple burr holes, cervical carotid sympathectomy, and omental transplantation.

In the multiple burr holes procedure, multiple small holes (burr holes) are placed in the skull to allow for growth of new vessels into the brain from the scalp.