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Acquired Chiari malformation type I following fractionated radiation therapy to the anterior skull base in a 20-month-old boy. Case report.

The authors present the case of a 20-month-old boy who underwent fractionated radiation therapy to the paranasal sinuses and anterior skull base during treatment for nasopharyngeal parameningeal rhabdomyosarcoma. Subsequent magnetic resonance imaging demonstrated progressive development of a Chiari malformation Type I (CM-I) and partial hypoplasia of the posterior fossa. Since the tonsillar herniation was discovered, the child, now 3 years old, remains asymptomatic except for mild, intermittent neck discomfort. For the time being, his family has elected for him to undergo clinical and neuroimaging follow up. The authors believe this is the first report of a progressive acquired CM-I after cranial irradiation in the pediatric population.