Moyamoya Disease

Moyamoya disease is a vasculo-occlusive disease involving the circle of Willis, typically the terminal ICA. 

The term moyamoya disease should be reserved for an idiopathic, sometimes familial, condition, which leads to characteristic intracranial vascular changes.  Numerous entities have been described which mimic the appearance, in which case the term moyamoya phenomenon, syndrome or pattern is used. 

This article concerns itself with moyamoya disease. For a list of conditions that can mimic moyamoya please refer to the article on moyamoya syndrome, or the differential diagnosis list at the end of the article. 

Epidemiology

Moyamoya is a disease of children and young people, with a bi-modal age distribution 6:

early childhood : peak ~ 4 years of age

middle age : 30-40 years of age

The condition was initially described in Japanese patients, where it is still most common, in which 7-10% of cases are familial.

Clinical presentation 

Presentation is to some degree age dependent. 

In children hemispheric ischaemic strokes are most pronounced, whereas in adults haemorrhage from the abnormal vessels is more common 6. Watershed infarcts are also very commonly identified. 

Radiographic features

Moyamoya affects the distal ICA and circle of Willis. Small abnormal net-like vessels proliferate giving the characteristic "puff of smoke" appearance on direct angiography. CTA and MRA is not always able to demonstrate this appearance on account of lower flow and spatial resolution. 

Although classically described affecting the ICA, over 50% of patients also have involvement of the posterior cerebral arteries. 

Collateral circulation forms from a number of sources:

via the abnormal moyamoya vessels

pial collaterals from less affected vessles (especially PCA) : forming the so called ivy sign on contrast enhanced MRI

transdural branches of the middle meningeal and other dural branches

Staging 

See: moyamoya staging (Susuki)

Treatment

Bypassing the occlusive segments is the aim of most surgical therapy. 

In adults external carotid artery to middle cerebral artery (ECA-MCA) anastamoses can be performed as the vessles are larger. One of the surgical option is  superficial temporal artery to middle cerebral artery (STA-MCA) bypass. 

Encephaloduroarteriosynangiosis is the treatment of choice in pediatric patients as thier vessles are too small to allow direct anastomosis.

Etymology

The term moyamoya comes from "a Japanese expression for something hazy just like a puff of cigarette smoke drifting in the air"  was first described by Suzuki and Takaku in 1969 1.

Differential diagnosis

A number conditions can lead to imaging appearances that are very similar to moyamoya disease. For a full list please refer to moyamoya syndrome:

• cranial radiotherapy
• atherosclerosis
• phakomatoses 
• neurofibromatosis type 1(NF1)
• tuberous sclerosis (TS)
• infection
• tuberculous meningitis
• bacterial leptomeningitis
• post-varicella vasculitis 
• connective tissue disorders
• systemic lupus erythematosus (SLE)
• haematological disorders
• sickle cell disease
• antiphospholipid syndrome
• aplastic anaemia