**5. Pathophysiology**

In patients with this condition, large intracerebral arteries show a variable degree of stenosis and occlusions. Vascular intima shows fibrocellular thickening; elastic internal lamina will be tortuous, duplicate or triplicate; and the media show attenuation. Vessels may be dilated and thin-walled or thick-walled and stenosed in different regions. The hallmark of MMD is the meshwork of dilated vessels called moyamoya vessels (**Figure 1**). Aneurysms can form in some parts of cerebral vasculature as well.

**Figure 1.** *Pathophysiology of moyamoya disease (modified from [29]).*
