Steal phenomenon through the anterior communicating artery in Moyamoya disease.

Branch occlusion of the anterior cerebral artery (ACA) is regarded as a part of Moyamoya disease. The purpose of this study is to define the ACA steal phenomenon (SP) in Moyamoya disease and to evaluate temoporal changes according to the disease progression. From 139 Moyamoya patients we defined ACASP as narrowing of the ipsilateral A1-2 junction while preserving the anterior communicating artery and supplying the contralateral ACA cortical branches with the development of leptomeningeal collaterals by the ipsilateral middle cerebral artery into the hypoperfused ipsilateral ACA territory. Direction of the steal related to the stage in both hemispheres by Suzuki classification was statistically analyzed using the binomial test based on binomial distribution. Follow-ups of ACASP were evaluated in five patients. We identified ACASP in 13 (9%) patients (male:female=7:6, mean age 18 years, range: 2-58 years) of the 139 study patients. The presenting pattern was ischemic in 12 and hemorrhagic in one. The direction of SP occurred from the hemisphere in the lower to the higher stage of Suzuki classification (two-tail P value=0.0002). After revascularization surgery, ACASP disappeared or diminished. ACASP may occur in bilaterally different stages of Moyamoya disease as a transient self-adaptive process. It regresses after revascularization surgery.