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Arnold-Chiari malformation
Other Resources UpToDate PubMed

Arnold-Chiari malformation

Contributors: Andrea Wasilewski MD, Richard L. Barbano MD, PhD
Other Resources UpToDate PubMed


Arnold-Chiari malformation, also known as type II Chiari malformation (type II CM) or classic CM, is a structural defect in the skull base that results in the brainstem and cerebellum extending below the foramen magnum into the cervical spinal canal. Chiari defects are either primary (congenital) or secondary (due to trauma, disease, or infection). They are categorized by severity from grade I (asymptomatic to mildly symptomatic) to IV (most severe). The prevalence of CMs is approximately 1 in 1000 with the majority of cases (type I CM) being asymptomatic. Higher grades of Chiari malformations are associated with more severe symptoms. Chiari I and II malformation are more common in females than in males. The focus of this summary is type II CM.

Type II CM is usually diagnosed in infants and young children. It is almost always associated with myelomeningocele (spina bifida). Manifestations in infants include dysphagia and difficulty feeding, stridor, episodes of apnea, and extremity weakness due to brainstem dysfunction. Manifestations in childhood include progressive hydrocephalus and syringomyelia; scoliosis may occur.

Common complaints in children include severe head and neck pain, occipital headache, blurred vision, dizziness, balance issues, and spasticity. Type II CM often results in the development of a syrinx (a fluid-filled cavity in the spinal cord). More severe symptoms include limb weakness, changes in breathing patterns (apnea), or abnormal eye movements (nystagmus).


Q07.00 – Arnold-Chiari syndrome without spina bifida or hydrocephalus
Q07.01 – Arnold-Chiari syndrome with spina bifida
Q07.02 – Arnold-Chiari syndrome with hydrocephalus
Q07.03 – Arnold-Chiari syndrome with spina bifida and hydrocephalus

373587001 – Chiari malformation type II

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Vertigo
  • Cerebellar ataxia
  • Cervical spondylosis
  • Cervicogenic headache
  • Occipital neuralgia
  • Sleep apnea
  • Laryngeal nerve paralysis
  • Pseudotumor cerebri
  • Syrinx
  • Intracranial hypotension (idiopathic versus traumatic versus iatrogenic from lumbar puncture or shunt)

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Last Reviewed:03/12/2018
Last Updated:04/11/2022
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Arnold-Chiari malformation
A medical illustration showing key findings of Arnold-Chiari malformation : Headache, Ataxia, Dysarthria, Hyperreflexia, Neck pain, Nystagmus
Copyright © 2023 VisualDx®. All rights reserved.