**1. Introduction**

Moyamoya disease is a cerebrovascular ailment that entails a progressive steno-occlusive process of the terminal internal carotid artery and its main branches. Secondarily it induces the development of an extensive network of unusual reticular collateral vessels at the skull base, mainly at the lenticulostriate and choroidal arteries [1–4]. These abnormal vessels create a hazy picture on cerebral angiogram that looks like a "puff of cigarette smoke drifting in the air" [5], which is the meaning of moyamoya in the Japanese language. These abnormal collateral vessels undergo pathological changes that lead to the appearance of haemorrhages [6].

Moyamoya disease leads to ischemic and haemorrhagic brain strokes and induces cognitive impairment [2, 7–9], partly due to the cerebrovascular insults [8], chronic brain hypoperfusion and white matter involvement [10]. The cognitive decline seems to be more severe in the haemorrhagic than in the ischemic type [11]. Disease progression is typical if left untreated [12].

Moyamoya disease aetiology is mostly unknown [13, 14], and without precise knowledge in this area, it is challenging to devise an effective treatment that prevents and cures this disease.
