Moyamoya Vessels (Abnormally proliferating arteries?) Due to progressive steno-occlusive changes of the internal carotid arteries and/or middle cerebral arteries at the base of the brain, essentially normal small arteries (diameter: 100-300 microns) become prominent and enlarge, which can be easily recognized on angiograms. These vessels mimic the puff of the cigarette smoke, thus called "moyamoya vessels". These vessels are not the abnormal neoplastic vessels, such as the vessels feeding the tumor. Pre-existing normal small vessels in the deep brain structure have to be collateral pathway to the ischemic brain. Due to excess burden to these moyamoya vessels, they occasionally rupture and cause brain hemorrhage. Moyamoya vessels are prominent in children, but not so in adults. This is believed that the vessels in children are more flexible and plastic than those in adults.

Perforating arteries (Arrow: moyamoya vessels)