Moyamoya is a Japanese term which translates in english to: “cloudof smoke” or “puff of cigarette smoking drifting in the air” and it has been used to define a classic angiographic appearance of multiple small intracranial vessels . Although described first in Japan in the 1950s this form of cerebrovascular disease is not limited to the Japanese population and has been reported sporadically all over the world with cases described in the United States, Europe, Australia and Africa. The incidence seems to be roughly one in a million people per year. There seem to be two definite peaks of incidence: children under 10 years old and adults in their third to fifth decades of life. A slight female preponderance has been shown. There is some evidence of familial tendency based on association between moyamoya and certain HLA types. Familial incidence is estimated about 7 to 12% around the world.
The Moya moya pattern of vessels seen on angiography is thought to be a phenomena secondary to intracranial large vessel narrowing or stenosis. The response of the cerebral vasculature to this type of narrowing is for more distal vessels to proliferate. There is debate as to whether the vascular abnormality represents a congenital problem or an acquired stenosis of intracranial vessels that occurs early in life. Moyamoya type changes have been found in a variety of diseases, including sickle-cell disease, neurofibromatosis, trisomy 21 and fibromuscular dysplasia. Other predisposing conditions for this problem include an auto immune process, cranial trauma, anaerobic bacteria or the use of oral contraceptive but none has been convincing. There are no specific symptoms or signs related to moyamoya syndrome. The various clinical manifestations are generally caused by cerebrovascular ischemic or hemorrhagic events. Headaches and seizures are also seen. Clinically the disorder presents in children with transient ischemic attacks (TIA) frequently with episodes of hemiparesis or other focal neurological signs, often precipitated by physical exercise or hyperventilation. There may be a more chronic course of worsening with a gradual impairement of intellectual deterioration. Adults in contrast, usually present with intracerebral hemorrhage, most frequently in the thalamus, basal ganglia or deep white matter. Subarachnoid or intraventricular hemorrhage may also be observed. Other signs and symptoms seen in children and adults are disturbance of consciousness, speech disturbance, sensory impairment, involuntary movement and visual disturbance. The prognosis of moyamoya is difficult to predict because the natural history of the disease is still unclear. Autopsy studies have shown severe vascular occlusive changes in the intracranial portion of the ICA usually bilateral and in the main arteries that make up the circle of Willis. These changes are characterized by endothelial hyperplasia and fibrosis with intimal thickening and abnormalities of the internal elastic lamina, while the adventitia and media remain normal. Descriptions of the vertebrobasilar system are not available. Extracranial arteries at the level of heart, kidney and other organs may show the same intimal lesions as the intracranial arteries supporting the belief the moyamoya syndrome can be a more generalized systemic vascular syndrome. Inflammatory cells or atheroma are not typically seen. The intracerebral perforating arteries around the circle of Willis show micro aneurysm formation with fibrin deposition and thinning of the vessel wall. These types of changes are thought to be responsible for the occurrence of intracerebral hemorrhage. It is postulated that there is increased blood flow through these small fragile vessels making them prone to hemorrhage.Cerebral angiography is the cornerstone of the diagnosis of moyamoya syndrome. The characteristic angiographic findings of moyamoya syndrome are a symmetrical stenosis (tapering) or occlusion of the intracranial internal carotid artery, as well as the origin of the anterior and middle cerebral artery associated with an enlargement of the basal penetrating branches of these arteries in an apparent attempt to provide collateral circulation and giving the classic “cloud of smoke” appearance . Computed tomography scaning shows non specific findings. There may be ischemic areas of the cortex and sub cortical white matter with evidence of old areas of infarction. There may be mild ventricular dilatation or dilated sulci and fissures. In the case of intracerebral hemorrhage the CT scan will show the location of the intraventricular, subarachnoid nd intraparenchymal hemorrhage that usually occurs in the basal ganglia or thalamus .Magnetic resonance imaging may better visualize areas of cerebral infarction due to moyamoya. Usually these infarctions are multiple, small and asymptomatic.
Infarction is seen predominantly in the watershed areas of the carotid circulation at the borderzone between the areas of the brain supplied by the middle cerebral artery and anterior cerebral artery.Magnetic resonance angiography (MRA) can be used to detect the abnormal intracranial vessels although its resolution does not yet allow the visualization of the abnormal basal penetrating vessels. Other techniques including positron emission computed tomography(PET), single photon emission computed tomography (SPECT) and perfusion MRI studies have been used to study regional cerebral blood flow in moyamoya patients. There are still not enough available data to draw any conclusion about the usefulness of these techniques in the diagnosis of this condition. Transcranial Doppler has recently been used to study patients with moyamoya syndrome and has been shown to be a very useful non invasive technique to follow changes in larger vessels with time. The best treatment is not known. The treatment of moya moya patietns depends on the pattern of symptoms. For patients with ischemic events and infarction, medical therapy consists of management with steroids in certain instances. Aspirin, ticlopidine and occasionally vasodilators and anticoagulants may be used. No study has supported the definitive efficacy of any medical treatment. A variety of different surgical revascularisation procedures have been used, but whether they improve the outcome is not yet known. Superficial temporal artery-middle cerebral artery bypass, encephalodurosynangiosis,omentum transplantation and cervical sympathectomy are options. The main purpose of surgical procedures is to provide additional collateral flow to an are of ischemic brain and therefore to prevent further damage. Encephalodurosynangiosis (EDAS) is performed with the intent to divert flow from the external carotid artery into the internal carotid artery system by applying branches of the superficial temporal artery or the temporal muscle to the brain surface of a patient. Finally omentum transplantation is performed with the intent to revascularize ischemic tissue. Cervical sympathectomy including stellate ganglionectomy is performed with the intent of improving cerebral blood flow. For treatment of hemorrhage, hematoma evacuation and ventricular drainage are the usual methods of treatment. There is no specific medical or surgical therapy proven to reduce subsequent hemorrhage. Some patients with moyamoya stabilize clinically, often after they have developed disabilities, others continue to show progressive deterioration despite treatment.Although no definite effective treatment has been determined, surgical therapy to augment collateral circulation appears to be a promising treatment for patients with relapsing ischemic events.
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