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Introduction

This is a vasocclusive disease and is a cause of both ischaemic and to a lesser extent haemorrhagic stroke. It is rare in Europeans, mostly seen in Asians most commonly Japanese, Chinese and Koreans but it can occur in other non Asian populations. It may present in childhood. Familial cases are linked to a gene on Chromosome 17. The term 'Moyamoya' comes from the Japanese and means 'puff or smoke in the air or hazy' and is an allusion to the angiographic appearance of the extensive collateral vessels formed in the disease [Suzuki J et al. 1983]. The underlying lesion is progressive narrowing of the internal carotid arteries and development of collaterals from external carotid artery and the vertebrals and their branches. It is seen in up to 10 per 1000,000 in Japan but in the USA the incidence falls to less than 1 in 1,000,000.

Cases are both sporadic and familial. There is an association with Moyamoya and sickle cell disease, Beta thalassaemia, Neurofibromatosis type I, Fanconi anaemia, Hereditary spherocytosis, Homocystinuria and hyperhomocysteinemia, Factor XII deficiency and Essential thrombocythemia as well as SLE, Grave's Disease, APS and various other genetic disorders. The underlying aetiology is unclear and may consist of overexpression of angiogenic and endothelial growth factors. Increased levels of Basic fibroblast growth factor has been found in MMD which is one of several areas of further research.

There is progressive intracranial artery stenosis and occlusion of the internal carotid artery, Formation of fragile collateralisation arteries which can bleed. Aneurysms can also be found. Bleeding is seen more so in adults and is the main cause of mortality and morbidity. Bleeding is both from fragile collaterals and rupture of saccular aneurysms on the circle of willis or from dilated perforators [Kuroda S 2008].

Moyamoya disease can affect children and young people with TIA episodes. Most commonly Children present typically with recurrent episodes of sudden hemiplegia that might alternate sides. May also be strokes, chorea and seizures. It causes predominately ischaemic stroke but haemorrhagic stroke is also seen due to bleeding from fine collaterals and is commoner in Adults.

The Angiographic stages Modified from Suzuki [Suzuki 1969] by Burke [Burke et al. 2009]

StageDescription
1Stenosis of the suprasellar ICA usually bilateral
2Development of Moyamoya vessels with dilatation of all main cerebral arteries at base of brain
3Increasing ICA stenosis and prominence of Moyamoya vessels with reduction of flow in the middle and anterior cerebral arteries
4Entire Circle of Willis and PCAs occluded. Extracranial collateralisation with minimisation of Moyamoya vessels. Proximal portions of the posterior cerebral arteries become involved
5Reduction of Moyamoya and absence of all main cerebral arteries
6Disappearance of Moyamoya vessels and major cerebral vessels; the cerebral circulation is supplied only by the external carotid system

Investigations

CT Imaging can show either cortical or subcortical infraction and even some cortical volume loss. Subcortical lesions seem to occur earlier. CT can also show deep and lobar haemorrhage.

Diagnosis however requires angiography and MRI/MRA should be performed for the diagnosis. This shows carotid narrowing or occlusion in the distal internal carotid and fragile collateral vessels give traditional "puff of smoke" appearance on cerebral angiography. Gradient echo may show prior or new haemorrhage. The finding of dilated collateral vessels in the basal ganglia and thalamus can be demonstrated as multiple punctate flow voids and is regarded as virtually diagnostic of Moyamoya syndrome. FLAIR images and post contrast T1 images can show a linear pattern of increased signal in the leptomeninges and perivascular spaces. This pattern has been termed the "ivy sign", since it resembles the appearance of ivy creeping on stones. Transcranial Doppler ultrasonography if available is a noninvasive way to evaluate intracranial haemodynamics and large artery stenosis.

Management

Management includes medical and surgical options. Patients are referred to centres of excellence with experience in this disease. Medical options are unproven but include vasodilators and some would avoid antiplatelets especially in older patients.General blood pressure management would seem wise. Most would consider surgery in symptomatic patients. There are a variety of procedures to increase blood supply to increase. Surgical treatments are divided into 3 types: direct, indirect, and combined/other methods. Direct bypass includes superficial temporal artery (STA) to Middle cerebral artery (MCA) anastomosis or use of other graft types. Indirect procedures bring in circulation to the intracranial regions by introducing newly developed vasculature from newly approximated tissues. The first involves anatomising the superficial temporal artery (STA) to middle cerebral artery (MCA) bypass is considered the treatment of choice, Children are given aspirin but without any real evidence base and it is stopped in adults due to risk of bleeds. Haemorrhagic lesions are the commonest cause of death.


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