Which of the following is associated with platybasia and malformation of the occipi- tovertebral joint?

D. Arnold-Chiari syndrome, a common congenital malformation, is frequently associated with platybasia and malformation of the occipitovertebral joint; other anomalies frequently seen are beaking of the tectum, aqueductal stenosis, kinking and herniation of the medulla, and herniation of the cerebellar vermis through the foramen magnum. Meningomyelocele (spina bifida) is a common component of the syndrome.