Chiari II Malformation and Syringomyelia

Abstract

The Chiari II malformation was described at the end of the nineteenth century (1891–1896) by Hans Chiari, a German pathologist, as a congenital malformation in a post-mortem examination of a child who died from a constellation of malformations including prolapse of the cerebellum, part of the brain stem and part of the hindbrain, involving the upper part of the cervical spine, with hydrocephalus and myelomeningocele. Around the same time (1894) similar observations were made by Arnold, hence the malformation is often called the Arnold-Chiari malformation. Cleland made similar observations in 1883 and 1913. Subsequently, the term Chiari malformation has been used to describe all forms of hindbrain herniation, of which three subtypes have been described. Chiari type I malformation refers to the prolapse of the cerebellar tonsils more than 5 mm below the foramen magnum, with no spina bifida malformation. In severe forms of Chiari I malformation there may be some brain stem descent, and occasionally this is incorrectly called a Chiari II malformation. The term Chiari II should only be used for patients born with spina bifida aperta (myelo menin go cele) and hindbrain herniation. Equally incorrect is the labeling of a mild hindbrain herniation in children with spina bifida aperta as a Chiari I malformation.