Inclusion Criteria:  Having a social security Participant or legal representative having given his consent For patients: Diagnosis of a Chiari malformation type 1, defined morphologically as cerebellar tonsillar herniation beyond the foramen magnum greater than 5 mm, with or without associated syringomyelia, and which has at least one relating to the 1st or 2nd degree (parents, siblings; grandparents, uncles, aunts, cousins) carrying the malformation. For relatives: at least two 1st degree relatives diagnosed with a Chiari type 1 malformation  Exclusion Criteria:  Syndromic form of Chiari malformation Patient with a legal protection measure Pregnant or breastfeeding woman Contraindication to MRI For patients: diagnosis of Chiari malformation type 1 that could not be confirmed by MRI For relatives: age under 18 years