Brain conditions

Chiari malformations

Chiari malformations are characterised by abnormalities at the base of the skull where it meets the spine. You can either be born with a Chiari malformation or acquire one.

There are several types of Chiari malformations, which have been categorised by German pathologist Professor Hans Chiari, who first recognised such defects.

Type I Chiari malformation

A Type I Chiari malformation occurs when the cerebellar tonsils are positioned downwards in the cervical spinal canal below the foramen magnum. The foramen magnum is the opening at the skull’s base that allows the spinal cord to enter and connect to the brain stem.

The two cerebellar tonsils normally protrude below the cerebellum, which is made up of two hemispheres joined at the base by the corpus callosum.

A Chiari I malformation may or may not cause symptoms.

Type II Chiari malformation

A Type II Chiari malformation occurs when the medulla, fourth ventricle and the cerebellum are displaced into the cervical spinal canal. The pons and fourth ventricle are also lengthened.

This mostly occurs in people who have myelomeningocele, a medical condition that involves the spinal cord and column not properly closing in a fetus.

What are symptoms of Chiari malformations?

Chiari malformation symtoms include:

  • severe headaches including one at the skull base that is exacerbated by sneezing or coughing
  • neck pain
  • pain and temperature loss in the upper torso and arms
  • collapsing that results from muscle weakness
  • dizziness or impaired vision
  • waining muscle strength in arms and hands
  • sensitive to light
  • spasticity

How are Chiari malformations treatment?

To treat a Chiari malformation, a neurosurgeon may take a “wait and see” approach and recommend observing it first.

They will perform surgery if needed.



  1. Brain Foundation, Chiari malformation.