Abstract
BACKGROUND: This study reports a case investigating the long-term progression of moyamoya disease (MMD) involving a duplicated middle cerebral artery (MCA). MMD is characterized by progressive stenosis of the terminal internal carotid artery (ICA) and its terminal branches, which is accompanied by the formation of collateral vessels. OBSERVATIONS: A 49-year-old Japanese woman diagnosed with MMD at 38 years of age was found to have a duplicated right MCA through digital subtraction angiography. Two years after the diagnosis, the vascular lesion progressed, leading to dropout of the right proximal anterior cerebral artery and disappearance of the bilateral anterior cerebral artery. She experienced a transient ischemic attack 2 years after the diagnosis and underwent bilateral revascularization. Eleven years of follow-up revealed no stenosis in either the MCA or ICA. LESSONS: The progression of MMD may be attributed to shear stress that might have weakened the ICA distal to the duplicated MCA. Blood flow to the duplicated MCA was maintained, and the proximal ICA did not develop stenosis due to the preservation of shear stress. https://thejns.org/doi/10.3171/CASE2598.