*Surgical Treatment of Moyamoya Disease DOI: http://dx.doi.org/10.5772/intechopen.99776*

Microbleeds' are more common in MMD than in the general population [87] and usually in the periventricular areas, followed by the basal ganglia and thalamus [87–89]. The asymptomatic microbleeds are related to hypertrophy, dilatation and aneurysm formation of the posterior communicating and anterior choroidal arteries [90–92]. Those areas are where the MMD related haemorrhagic strokes typically happen, and these microbleeds are an excellent prognosticator of future haemorrhages [83, 93, 94].

Asymptomatic MMD patients have a 3.2% annual stroke risk [95], more often haemorrhagic than ischemic, showing an evolving situation that is usually is not silent nor stable [72, 96], particularly in those with a compromised CVR capacity [97]. Moreover, cognitive decline over time is the rule [98]. Thus, asymptomatic MMD patients should be monitored closely and submitted to surgical BR at the slightest sign of deterioration [99].

Although there might be a subgroup of children with a benign course [100], most have a relentless and progressive worsening [99], and unilateral disease often evolves to bilateral [99]. Predictors of unfavourable outcome are onset at a younger age, a long time before BR, brain infarcts, and PCA involvement [86]. Children under nine years of age with minor changes in the contralateral brain hemisphere are most likely to undergo disease progression [101, 102].

This disease, particularly if untreated, can induce severe disability and even death [3]. White matter involvement, particularly in adults, correlates with cognitive impairment [57].
