Moyamoya Disease and Cerebral Blood Flow Cerebral blood flow is maintained even in the hypertensive or hypotensive state. This is called "Cerebral Autoregulation". When the cerebral blood flow (CBF) drops below the critical level, cerebral infarction occurs. However, when the CBF drops to some extent, autoregulation was maintained by the first step (vasodilation of the small arteries - arterioles). Further compromise necessitates the second step (increased oxygen consumption). When these two steps are not enough, it results in . In moyamoya disease, the terminal portions of the internal carotid arteries are steno-occlusive. The CBF is maintained by the above-mentioned two mechanisms. When the CBF drops furthermore, or thrombus is formed in the cerebral arteries compromising the blood flow, transient ischemic attack or cerebral infarction occurs. By surgical anastomosis, compromised CBF was augmented by the blood flow from outside the brain. To our knowledge, there has been no medical treatment to overcome the decreased CBF. To examine the CBF, positron emission CT or single photon CT, or xenon inhalation CT are commonly used. Recently, perfusion x-ray CT and MRI with contrast materials are used for this purpose. Takeuchi et al reported on the CBF in moyamoya disease. Takeuchi S, Tanaka R, Ishii R, et al: Cerebral hemodynamics in patients with moyamoya disease. A study of regional cerebral blood flow by the Xe-133 inhalation method. Surg Neurol 23:468-474, 1985 Abstract: Regional cerebral blood flow was measured by the Xe-133 inhalation method in 20 young patients with moyamoya disease and five young healthy volunteers. Most patients showed low values of mean hemispheric blood flow in both hemispheres. Regional cerebral blood flow was at a low value in the upper frontal region and at an almost average value in the posterotemporal and occipital regions, which was different from the "hyperfrontal" pattern in healthy volunteers. Regional cerebral blood flow was reduced evenly by hyperventilation. By 5% CO2 inhalation, regional blood flow was increased in the temporooccipital regions and was nearly unchanged or decreased in the frontal region.