1. From the Divisions of Pediatrics in the Departments of Radiology (N.R.), Neurosurgery (N.R., B.B.), and Neurology (M.D.), Children’s Health System of Texas, University of Texas Southwestern Medical Center, Dallas; and Anesthesia for Children (A.H.) and Center for Cerebrovascular Disease in Children (S.B.), Children’s Health System of Texas, Dallas.