A male newborn infant is brought to the clinic by his mother and diagnosed with a congenital malformation. MRI studies reveal that the cerebellum and medulla oblongata are protruding inferiorly through the foramen magnum into the vertebral canal. What is this clinical condition called?

Arnold-Chiari malformation results from herniation of the medulla and cerebellum into the foramen magnum. Meningocele is a small defect in the cranium in which only the meninges herniate. Klippel-Feil syndrome results from an abnormal number of cervical vertebral bodies. Hydrocephalus results from an overproduction of cerebrospinal fluid, obstruction of its flow, or interference with CSF absorption. Tethered cord syndrome is a congenital anomaly caused by a defective closure of the neural tube. This syndrome is characterized by a low conus medullaris and a thick filum terminale.