**1. Introduction**

Moyamoya disease is a chronic steno-occlusive cerebrovascular disease characterized by progressive occlusion of bilateral distal ICA with a fine basal collateral network development. Long-term hemodynamic stress through the basal collateral network leads to cerebral ischemia and intracranial hemorrhage in children and adults, respectively. The study from Japan in 2007 reported the annual risk of any stroke as 3.2% in 34 non-surgically treated Moyamoya patients (mean follow up over 44 months) [1, 2].

Progressive stenosis of distal intracranial internal carotid arteries with a smoke-like appearance from collateral vessels in angiography is characteristic of Moyamoya disease [3]. The stenosis usually remains progressive until occlusion and flow diminish. Hemodynamic collapse is a primary mechanism for an ischemic event in Moyamoya disease. The preferred treatment for cerebral ischemia focuses on the correction of hemodynamic failure. This rationale makes surgical treatment essential, and medical management is not a principle for Moyamoya patients [4].

The name of moyamoya means puff of smoke, which refers to the collateral circulation's angiographic appearance. These collaterals are bundles of small, fragile arterioles that vulnerable to break out. The rupture of weak collateral vessels in Moyamoya disease is a primary mechanism for a hemorrhagic event. Revascularization surgery can reduce overload in collateral vessels, which prevents the vessels from getting ruptured [5]. In contrast, primary intracerebral hemorrhage is related to chronic hypertension [6]. The role of blood pressure control with antihypertensive drugs is not entirely clear for intracranial hemorrhage prevention in Moyamoya patients.
