Chiari Malformations
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Chiari malformation refers to a condition where part of the cerebellum is positioned within the foramen magnum. There are four types, Chiari II and Chiari II (also sometimes referred to as Arnold-Chiari malformation) and Chiari III & IV – these last tow types are very rare.

Chiari type I

  • The cerebellar tonsils are displaced into the upper cervical canal
  • The tonsils themselves are often elongated and sometimes referred to as ‘peg-like’
  • There may be associated abnormalities of the skull and cervical vertebrae
  • Clinically tends to have the mildest symptoms – many cases are asymptomatic
  • Incidence of about 1 in 2000
Chiari I malformation
Chiari I malformation on MRI. This file is taken from wikimedia commons and is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Chiari type II

  • Displacement of the medulla, 4th ventricle and cerebellum into the spinal column
  • Usually associated with myelomeningocoele – which is a congenital defect whereby part of the spinal cord develops outside of the body, contained within a fluid-filled sac, and is seen in certain severe cases of spina bifida
Chiari II malformation
Chiari II malformation on MRI. This file is taken from wikimedia commons and is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Chiari II malformation
Chiari I malformation on MRI. This file is taken from wikimedia commons and is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Chiari type III

  • Similar to type II Chiari malformation – this is a variation of spina bifida that involves herniation of the cerebellum into the spinal column

The condition is named after Hans Chiari – a German pathologist who described various neurological abnormalities in the 1890s.


Presentation can vary widely depending on the degree of herniation. Cases of type I Chiari malformation may be asymptomatic. The degree of symptoms is often dependent on the flow of CSF – in more symptomatic cases there is more likely to be disruption of the flow of CSF and it may even flow in a caudal to cranial direction.

Type I Chiari Malformation

Presentation can occur at any stage of life. More severe cases tend to present earlier.

  • Headaches – usually occipital and neck regions
    • Periorbital pain is also common
  • Visual distrubance
    • Diplopia
    • Photophobia
  • Dizziness, vertigo, nystagmus
  • Cerebellar signs
    • Ataxia
    • Dyshphagia
    • Dysphasia
  • Spinal cord related signs
    • Altered sensation
    • Altered motor function
    • Torticollis
    • Bladder or bowel symptoms
  • Other neurological signs
    • Weakness
    • Paraesthesia
    • Cranial nerve palsy
  • Skull and vertebrae abnormalities in up to 50% of cases

Type II Chiari Malformation

Typically presents at a young age (sometimes as early as the neonatal period). Assocaited with significant mortality and morbidity. There are typically two types of presentation – those in infants and those in adolescents.

  • Only seen in individuals with meningomyelocele – which is seen in more severe cases of spina bifida
    • Occurs in 30% of cases of meningomyelocele
  • Mortality at age of 5 years is about 30%
  • Associated with significant cranial nerve and brainstem dysfunction


  • Stridor
  • Dysphagia
  • Nasal regurgitation
  • Aspiration
  • Apnoeic episodes
  • Weak cry
  • Quadriparesis
  • Scoliosis


  • Symptoms often progressive
  • Nystagmus
  • Syncope
  • Quadriparesis – typically with UMN signs
  • Recurrent episodes of aspiration and aspiration pneumonia


  • MRI
    • The gold standard investigation
    • With contrast may provide better quality images for diagnosis of Chiari malformation
    • Cine MRI may help to determine CSF flow
  • X-ray
    • Of the skull and spinal cord can show structural deformities
  • CT
    • Less useful than MRI
    • May show ventricular abnormalities of the 4th ventricle
  • USS
    • Can be used in neonates with an open fontanelle
    • Used mainly as a screening tool where appropriate


All patient should be offered rehabilitation therapy. Surgery is indicated in many cases.

Patients with obvious reproducible neurological sings – such as nystagmus, or specific weakness are most likely to benefit from surgery.

Chiari I

  • MDT approach to determine the indication for surgery
  • In particular – a close assessment of the symptoms in relation to the visualised structural abnormalities should be made
  • Typical surgical therapies might include craniectomy and/or upper cervical laminectomy to decompress the malformation.
    • This is often effective at preventing further deterioration but may not improve ongoing symptoms
  • A shunt may also be used, even without the presence of hydrocephalus
  • There are some case reports of spontaneous resolution of Chiari I
  • Many cases are asymptomatic and do not require intervention

Chiari II

  • Earlier surgery is associated with better long-term outcome


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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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