Chiari malformation

Arnold-Chiari malformation is a congenital developmental abnormality of the hindbrain. It is a congenital hindbrain malformation in which embryonic developmental abnormalities cause the lower medulla oblongata and the lower portion of the fourth ventricle to herniate into the spinal canal, with the cerebellar tonsils elongated into a wedge shape and entering the foramen magnum or cervical spinal canal. In severe cases, part of the inferior vermis also herniates into the spinal canal, and the lower cranial nerves including the glossopharyngeal, vagus, accessory, and hypoglossal nerves, as well as the upper cervical nerve roots, are stretched and displaced downward. The foramen magnum and upper cervical spinal canal become filled, and cerebrospinal fluid circulation is obstructed, causing hydrocephalus. Arnold-Chiari malformation is often accompanied by other craniovertebral junction abnormalities such as myelomeningocele, cervical spina bifida, and cerebellar hypoplasia.