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Arnold-Chiari malformation

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A condition in which the inferior poles of the cerebellar hemispheres (cork-like protrusions) and the medulla oblongata protrude through the foramen magnum into the spinal canal, without displacing the lower brain stem. This results from a developmental deformity of the occipital bone and upper end of the cervical spine. It is one of the causes of hydrocephalus and is usually accompanied by spina bifida and meningomyelocele. It may be associated with stenosis of the aqueduct of Sylvius with obstructive hydrocephalus, and atrophy of the brain tissue.

Both sexes affected; onset usually in 3rd or 4th decade. Symptoms may appear in childhood. Headache, vomiting, visual disturbances, diplopia; mental dullness, lack of coordination, paralysis of extremities, cerebellar ataxia, and sensory disorders Aetiology unknown.

This is Chiari's classification of deformities of the cerebellum and brainstem in children with herniation of the spinal cord:

Type I: Complete or partial herniation of the cerebellum-tonsils below foramen magnum.

Type II: Herniation of vermis and pons down into to cervical canal. Small, dilated 4th ventricle.

Type III: High cervical or occipitocervical hernia containing cerebellum-tissue.

Type IV: Hypoplasia of the cerebellum sometimes associated with encephalocele.

The first description of malformations of the brainstem and the cerebellum in children with herniation of the spinal cord was made by John Cleland, ten years before Hans Chiari and Julius Arnold, whose names the condition now bears.


  • J. Cleland:
    Contribution to the study of spina bifida, encephalocele and anencephalus.
    Journal of Anatomy and Physiology, 1883, 17: 257.
  • J. Arnold:
    Myelocyste, Transposition von Gewebskeimen und Sympodie.
    Beiträge zur pathologischen Anatomie und zur allgemeinen Pathologie, 1894, 16: 1-28.
  • H. Chiari:
    Über Veränderungen des Kleinhirns infolge von Hydrocephalie des Grosshirns.
    Deutsche medicinische Wochenschrift, Berlin, 1891, 17: 1172-1175. Über Veränderungen des Kleinhirns, der Pons und der Medulla oblongata, infolge von congenitaler Hydrocephalie des Grosshirns.
    Denkschriften der Akademie der Wissenschaften in Wien, 1895, 63: 71.

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