Inclusion Criteria- Adult > 18 years of age
- Capable of informed consent
- Clinical: Both asymptomatic and symptomatic patients will be included.
- Anatomic: Unilateral or bilateral imaging findings consistent with moyamoya collaterals (Suzuki stages 3 and 4) on digital subtraction, computed tomographic, or magnetic resonance angiography (after Suzuki and Kodama, 1983)
Exclusion Criteria- Any other disease that might be responsible for the vasculopathy, including atherosclerosis, neurofibromatosis, meningitis, sickle cell disease, skull base radiation therapy.
- Pregnancy: All women of child-bearing potential will be tested for pregnancy on the day of the enrollment and throughout the course of the study.
- Surgery: Prior open or endovascular revascularization procedures, unless there have been ischemic symptoms since surgery and angiographic evidence that the procedure was not successful