Chiari Malformations

Original Editor - Wendy Walker

Lead Editors  

Clinically Relevant Anatomy

Chiari malformations are a group of defects associated with congential caudal 'displacement' of the cerebellum and brainstem.

They are named after Hans Chiari, the pathologist who first described the whole group of malformations.

Types of Chiari Malformations

Chiari I

This is the most common variant. 

Peg-like cerebellar tonsils are displaced into the upper cervical canal through the foramen magnum.

Radiologically if a person has a 5mm or more herniation below the foramen magnum it is classified as Chiari type I

Chiari 1.5

Described in the literature as both a condition in its own right as well as a variant of Chiari I malformation

Chiari II

AKA Arnold Chiari Malformation.

Displacement of the medulla, fourth ventricle and cerebellum through the foramen magnum.
Usually with associated with a lumbosacral spinal myelomeningocoele.

Chiari III

Features similar to Chiari II but with an occipital and/or high cervical encephalocoele.

Chiari IV

The most severe variant.

Severe cerebellar hypoplasia without displacement of the cerebellum through the foramen magnum.
Thought likely to be a variation of cerebellar hypoplasia.

Clinical Presentation

Type I

Symptoms of Chiari I develop as a result of 3 pathophysiological consequences of the disordered anatomy:

1. compression of the medulla and upper spinal cord
2. compression of cerebellum,
3. disruption of CSF flow through foramen magnum.

Compression of cord and medulla may result in myelopathy and lower cranial nerve and nuclear dysfunction. Compression of cerebellum may result in ataxia, dysmetria, nystagmus, and dysequilibrium. Disruption of CSF flow through the foramen magnum probably accounts for the most common symptom, pain.

Type II

The pathophysiology of Chiari II is more complex. Although compressive mechanisms likely play a role, as in Chiari I, additional mechanisms may be operative in Chiari II. Stretching of abnormally oriented cranial nerves is believed to play a role.

Chiari II may become acutely symptomatic with shunt malfunction.

Intrinsic neuroembryological abnormalities in Chiari II are widespread and not limited to the posterior fossa (eg, heterotopias, gyral abnormalities, callosal and thalamic abnormalities, in addition to hydrocephalus and myelomeningocele), further complicating the pathophysiology of this disorder. Types III & IV

These more severe variants of Chiari malformations are almost always diagnosed in infancy as the child presents with severe neurological symmptoms.

Diagnostic Procedures

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Outcome Measures

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Management / Interventions

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Differential Diagnosis

Pain in neck or headache made worse by coughing or the valsalva manoeuvre are suggestive of Chiari malformations, as a result of increased CSF pressure.

Key Evidence

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Resources

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Case Studies

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References

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