This article includes discussion of Chiari malformation, Arnold-Chiari deformity, and Arnold-Chiari malformation. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Chiari malformation describes a group of structural defects of the cerebellum, characterized by brain tissue protruding into the spinal canal. Chiari malformations are often associated with myelomeningocele, hydrocephalus, syringomyelia, and tethered cord syndrome. Although studies of etiology are few, an increasing number of specific genetic syndromes are found to be associated with Chiari malformations. Management primarily targets supportive care and neurosurgical intervention when necessary. Renewed effort to address current deficits in Chiari research involves work groups targeted at pathophysiology, symptoms and diagnosis, engineering and imaging analysis, treatment, pediatric issues, and related conditions. In this article, the author discusses the many aspects of diagnosis and management of Chiari malformation.
• Chiari malformation describes a group of structural defects of the cerebellum, characterized by brain tissue protruding into the spinal canal.
• Chiari malformations are often associated with myelomeningocele, hydrocephalus, syringomyelia, and tethered cord syndrome.
• Although studies of etiology are few, an increasing number of specific genetic syndromes are found to be associated with Chiari malformations.
• Management primarily targets supportive care and neurosurgical intervention when necessary.
• Renewed effort to address current deficits in Chiari research involves work groups targeted at pathophysiology, symptoms and diagnosis, engineering and imaging analysis, treatment, pediatric issues, and related conditions.
The Chiari malformation, also known as the Arnold-Chiari malformation (or deformity), was first described by Cleland in 1883 in a child with spina bifida, hydrocephalus, and alterations of the cerebellum and brainstem (Cleland 1883; Schijman 2004). In 1891, Austrian pathologist Hans Chiari wrote an article titled “Concerning alterations in the cerebellum resulting from hydrocephalus.” He described elongation of the cerebellar tonsils and medulla below the plane of the foramen magnum in a 17-year-old woman, now referred to as a type 2 malformation. Chiari's subsequent studies expanded the spectrum of malformations in a classification system consisting of types 1, 2, 3, and later 4. Otto Mennicke also contributed to our understanding of tonsillar ectopia (Fries et al 2017). In 1907, Arnold was credited with publishing 4 additional cases, and his students Schwalbe and Gredig added his name to the nomenclature. Many authors consider Chiari's contribution to be primary and, therefore, suggest that this condition be designated as Chiari malformation, without including Arnold's name (Koehler 1991).
Chiari type 1 refers to herniation of the cerebellar tonsils alone, and radiologically as simple tonsillar herniation 5 mm or greater below the foramen magnum (Elster and Chen 1992); type 2 refers to herniation of both the cerebellum and lower brainstem; type 3 refers to a rare type of brainstem herniation in association with a cervical or occipital encephalocele; type 4 involves extreme cerebellar hypoplasia and caudal displacement of the posterior fossa contents. Two additional types of Chiari malformation have been described. Chiari type 0 is defined as syringohydromyelia with distortion of contents in posterior fossa but without cerebellar tonsillar herniation (Iskandar et al 1998; Tubbs et al 2004b). Chiari type 1.5 has been characterized as caudal migration of the brainstem and cerebellar tonsils often associated with syringomyelia but without spina bifida (Schijman 2004; Tubbs et al 2004b).