June 2003 - Volume 13 - Issue 2 - pp 105-112
Surgical Management of Chiari Malformation
Steinmetz, Michael P.; Benzel, Edward C.
The Chiari malformation is frequently encountered by neurosurgeons.
The pathogenesis and natural history of the malformation is unknown.
Patients often present with symptoms related to brainstem compression, hydrocephalus, syringomyelia, and/or cerebellar compression.
Some patients present vague symptoms or are asymptomatic. With the increased sensitivity of modern imaging, asymptomatic patients are seen more frequently.
Decisions for the surgical management of Chiari malformations are based upon clinical findings and correlative imaging findings.
Decompression of the craniovertebral junction in this patient population result in the majority showing improvement or stabilized symptoms.
In 1883 Cleland described patients with hindbrain herniation, downward displacement of the cerebellar vermis, and hydromyelia.
1 However, it was not until 1891 that Hans Chiari described the hindbrain malformation of posterior fossa herniation that now bears his name. In 1907, Arnold's group published a paper also describing hindbrain herniation.
2 Arnold's name was substituted for Cleland's and the phrase Arnold-Chiari malformation was coined.
3 Because of the minor contributions of Arnold, most refer to the condition simply as Chiari malformation.
The Chiari malformation is a congenital or questionably acquired hindbrain disorder. It is characterized by the caudal displacement of posterior fossa structures below the foramen magnum.
The malformation is described based on the structures that have herniated below the foramen magnum.
Type I is characterized by herniation of the cerebellar tonsils below the foramen magnum. It is associated with syringomyelia in about 50-75% of cases.
4 The type II malformation also has herniation of the cerebellar tonsils, but also includes herniation of the cerebellar vermis and part of the fourth ventricle.
Nearly all patients with myelomeningocele have an associated Chiari type II malformation.
The type III malformation is the most severe form. The entire contents of the posterior fossa are herniated below the foramen magnum.
This type is rare and is usually not compatible with long-term survival.
© 2003 Lippincott Williams & Wilkins, Inc.