The association of Chiari type I malformation and neurofibromatosis type 1.

The association of neurofibromatosis type 1 (NF1) with Chiari malformations of the cerebellum and brain stem has been reported on only two previous occasions. The pathogenesis of both conditions has remained unclear, although the Chiari type I malformation is most likely due to hypoplasia of the posterior fossa with subsequent extension of the cerebellum through the foramen magnum. NF1 is also associated with a variety of cerebral dysplasias. We present a patient with both of these dysplastic lesions whose Chiari malformation was asymptomatic.