Chiari Malformation

Chiari malformation is a structural defect in the part of the brain that controls balance called the cerebellum.

Normally the cerebellum and parts of the brainstem sit in an indented space at the lower rear of the skull, above the opening to the spinal canal (foramen magnum).  When part of the cerebellum is located below the foramen magnum, it is called a chiari malformation.

The resulting pressure on the cerebellum and brainstem when it falls below the foramen magnum may affect functions controlled by these areas and block the flow of cerebrospinal fluid to and from the brain.  This disruption in flow is significant because the cerebrospinal fluid is the clear liquid that surrounds and cushions the brain and spinal cord.

Chiari malformations may be congenital (present at birth) or may develop later in life if spinal fluid is drained excessively from the lumbar or thoracic areas of the spine either due to injury, exposure to harmful substances or infection.

Types of Chiari Malformation:

  • CM1: only the lower part of the cerebellum extends into the foramen magnum and typically appears in adolescence or adulthood.  These are the most common form of chiari malformation.
  • CM2 (classic CM or Arnold-Chiari malformation): both cerebellar and brainstem tissue extends into the foramen magnum.
  • CM3 both the cerebellum and brainstem protrude, or herniate, through the foramen magnum into the spinal cord and results in serious neurological defects. Part of the brain’s fourth ventricle may also protrude through the opening and into the spinal cord. In rare instances, the herniated cerebellar tissue can protrude out of the back of the head or the neck (occipital encephalocele). The covering of the brain or spinal cord can also protrude through an abnormal opening in the back or skull.
  • CM4: Quite rare it involves an incomplete or underdeveloped cerebellum (cerebellar hypoplasia).  The lower cerebellum is located further down the spinal canal, parts of the cerebellum are missing and portions of the skull and spinal cord may be visible.


Often asymptomatic but may include

  • Neck pain
  • Balance problems
  • Muscle weakness
  • Numbness or other abnormal feelings in the arms or legs
  • Dizziness
  • Vision problems
  • Difficulty swallowing
  • Ringing or buzzing in the ears
  • Hearing loss
  • Vomiting
  • Insomnia
  • Depression
  • Headache made worse by coughing, sneezing or straining
  • Hand coordination and fine motor skill impairment
  • Spinal curvature such as scoliosis or kyphosis among patients with CM1


To determine whether you have Chiari malformation, your doctor will examine your back and your medical history, and may order an X-ray, bone scan, myelogram, computed tomography (CT) scan and/or magnetic resonance imaging (MRI) to rule out another disorder as the cause of your symptoms.


If patient is asymptomatic or symptoms, such as pain, can be addressed with conservative therapies such as medication then surgery may not be recommended.

If however symptoms are already severe or worsening, surgery may be required to correct the structural/functional defects affecting the spinal cord and decrease the damage to the central nervous system.

  • Decompression surgery: to create more space for the cerebellum and to relieve pressure on the spinal column
  • Spinal laminectomy: to increase the size of the spinal canal and relieve pressure on the spinal cord and nerve roots.
  • The neurosurgeon also may make an incision in the dura (the covering of the brain) to examine the brain and spinal cord. Additional tissue may be added to the dura to create more space for the flow of cerebrospinal fluid.

Our neurosurgeons have trained to specifically treat chiari malformations.  They will discuss the best course of treatment for your individual condition and the risks and benefits of surgery with you.

References: National Institute of Neurological Disease and Stroke, American Association of Neurological Surgeons.


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