A 3-year-old girl presented with progressive macrocephaly and a history of open myelomeningocele surgically repaired at birth. She had no history of intracranial hemorrhage or meningitis. Physical examination showed head circumference >99th percentile (54 cm) and decreased lower extremity motor function. Neuroimaging revealed extreme communicating ventriculomegaly and strikingly turbulent intraventricular CSF flow in the setting of diffuse cortical atrophy (figure, A–C). A ventriculoperitoneal shunt was placed. Intraoperatively, her intracranial pressure was 18 cm CSF (13.2 mm Hg) (normal in children: 3–7 mm Hg). Postoperative imaging showed complete resolution of intraventricular CSF turbulence with a mild decrease in ventriculomegaly (figure, D–F). The patient continued to exhibit mild neurocognitive impairments with arrest of progressive macrocephaly.