Moyamoya disease

This is a non-inflammatory vasocclusive disease of ICA, MCA and ACA and is a cause of both ischaemic and to a lesser extent haemorrhagic stroke. The abnormal net-like vessels at the base of the brain seen in cerebral angiograms of this disease were described by most native speakers of Japanese as "Moyamoya," a Japanese expression for something hazy, such as a puff of cigarette smoke drifting in the air. The name was popularised by Jiro Suzuki. [Suzuki J et al. 1983]

About

• Described it in 1957 as "hypoplasia of the bilateral internal carotid arteries" in Japan [1]. Later characterised as "Moyamoya" in 1965.
• 10 per 100,000 in Japan but in USA 1 in 1,000,000.
• Increased levels of Basic fibroblast growth factor has been found
• Progressive intracranial internal carotid artery occlusion with build-up of extensive fragile collaterals which can bleed
• Cases are both sporadic and familial.
• Can cause ischaemic and haemorrhagic stroke

Genetics

• Commonest in Asian (Japanese, Chinese and Koreans) it does occur in other non-Asian populations.
• Seen in White Europeans and Americans but 10 fold commoner in Japanese, Chinese and Koreans
• Familial cases are linked to a gene on Chromosome 17.

Aetiology

• Affects distal internal carotid artery and the stem of the MCA and ACA.
• Extensive collateralisation - with lenticulostriate and transdural anastomoses between the cortical surface branches of the meningeal and scalp arteries.
• Vascular inflammation is absent. Fragile arteries can bleed
• Similar disease may be seen with atherosclerosis and diabetes

Associations

• 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.

Clinical

• Affects young people and It may present in childhood.
• Children recurrent episodes of sudden hemiplegia that might alternate sides.
• Cognitive impairment with silent infarcts
• Ischaemic stroke and haemorrhage, seizures, chorea

Investigations

• Bloods: unremarkable usually (non-inflammatory vasculopathy)
• CT Imaging can show either cortical or subcortical infarction and even some cortical volume loss. Subcortical lesions seem to occur earlier. CT can also show deep and lobar haemorrhages.
• 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.
• MRI 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.
• MRI 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 non-invasive way to evaluate intracranial haemodynamic and large artery stenosis.
• EEG: Moyamoya syndrome-specific alterations of EEG recordings are only observed in children. These consist of a gradual frequency decrease and amplitude activation after hyperventilation. This is referred to as the re-build-up phenomenon. Thus, a tentative diagnosis of Moyamoya syndrome in children can be based on the EEG finding. This should be radiologically confirmed by angiography. [3]
• Perfusion studies: may show up areas of the brain at risk of ischaemia and infarction [4]

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.
• Surgical treatments are divided into 3 types: direct, indirect, and combined/other methods. Direct bypass includes superficial temporal artery (STA) or sometimes the occipital artery 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. Recent evidence tends to favour a direct strategy in reducing haemorrhagic risk.
• Multiple burr holes can aid revascularisation [5]
• 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.

Further Reading

• [1] Moyamoya Disease and Moyamoya Syndrome. N Engl J Med 2009;360:1226-37.
• [2] Moyamoya Disease: Treatment and Outcomes. J Stroke. 2016 Jan; 18(1): 21-30.
• [3] Characteristic EEG findings in childhood moyamoya syndrome.Neurosurg Rev 1992;15(1):57-60.
• [4] Comparison of MR Perfusion Weighted Imaging and CT Perfusion Imaging in Assessing Hemodynamics of Patients with Moyamoya Disease.Sichuan Da Xue Xue Bao Yi Xue Ban. 2018 Sep;49(5):749-753.
• [5] How I do it: operative nuances of multiple burr hole surgery for moyamoya disease and syndrome. Acta Neurochir (Wien). 2018 Nov 24. doi: 10.1007/s00701-018-3743-1